A Treatise on DIY Co2
Author: John LeVasseur
- Plants and CO2
- DIY CO2 Basics
- Some examples of system designs
- More than you need to know about yeast
- Guidelines for Mixtures and Capacities
- Construction Projects
- Conclusion
- Plants and CO2
- Carbon is the fundamental element that all life on this planet is based.
Plants are no exception. Since plants have no way of getting to their food
sources, nutrients have to be obtained from their surrounding environment.
Plants use many macro and micronutrients, carbon dioxide (CO2) being one of
the primary macronutrients. In an aquarium the limiting factors are most
likely to be (in order): light, CO2, micronutrients (trace elements), and
macronutrients. Micro and macronutrients are usually supplied in adequate
quantities by fish waste and the addition of fertilizers.
- Plants use a process known as photosynthesis to produce the carbohydrates
they need for life. Photosynthesis requires light for energy and CO2 to
drive the chemical reactions. The process of photosynthesis requires a
specific light energy threshold. In other words, there is a point where
light has reached a specific intensity to start photosynthesis. If the light
is not bright enough, photosynthesis will not occur. Beyond that threshold
and up to some high light level, photosynthesis will run faster and faster.
According to known practice, when light levels exceed two watts per gallon,
supplementary CO2 is required for most aquariums.
- In our planted aquariums, CO2 is present without it being added my
mechanical means. Fish respire CO2 from their gills. Also in an aerated
tank, CO2 from the atmosphere is dissolved in the water. This effect is
known as atmospheric equilibrium. In nature though, CO2 levels are usually
higher than can be explained by animal respiration or atmospheric
equilibrium, and aquatic plants have evolved to this higher concentration of
dissolved CO2 in water. Carbon dioxide rich groundwater often feeds the
streams and natural CO2 concentrations up to several hundred times
atmospheric equilibrium are common. In general, aquatic plants like to see
approximately a concentration of 10-15ppm of dissolved CO2 in their
environment. CO2 levels from atmospheric equilibrium are generally around
2-3ppm. (ppm stands for part per million). As you can see, CO2 injection is
essential for vigorous plant growth, and even more so with higher light
levels.
- As far a fish are concerned, high concentrations, CO2 can block the
respiration of CO2 from the fish gills and cause oxygen starvation. Since
the gills depend on a CO2 concentration differential between the levels in
the blood and the water to transfer gases, high levels in the water will
reduce the amount of CO2 that can be transferred. Although different
references have wildly varying values for toxic levels, a concentration of
below 30ppm is definitely safe.
- It is a common misconception that water can hold only so much dissolved
gas and adding CO2 will displace oxygen. This is not true. As a matter of
fact, if enough CO2 and light is present to enable vigorous photosynthesis,
oxygen levels can reach 120% of saturation. Even at night, when the plants
stop using CO2 and start using oxygen, the oxygen levels will stay about the
same as a typical non-planted aquarium. So reports of people having fish at
the surface gasping for air is not necessarily a result of high CO2 levels,
but instead a lack of oxygen in the water is probably the culprit.
- The relationship between light and CO2 levels is important. The diagram at
the right explains it conceptually. At low light and low CO2 there is not
much energy to play around with for up or down-regulation of the pools of
Chlorophyll or enzymes contained in the plant. If we then add a little more
CO2 to the system the plant can afford to invest less energy and resources
in CO2 uptake and that leaves more energy for optimizing the light
utilization - Chlorophyll can be produced without fatal consequences for the
energy. Hence, although we have not raised the light, the plant can now
utilize the available light more efficiently. Exactly the same explanation
can be used to explain why increased light can stimulate growth even at very
low CO2 concentrations. With more light available, less investment in the
light utilization system is necessary and the free energy can be invested
into a more efficient CO2 uptake system so that the CO2, which is present in
the water, can be more efficiently extracted.
- Providing macro and micronutrients to plants is easily done with
commercially available fertilizers. It is often a more difficult and
expensive task to provide adequate light over the plant aquarium. Both
numerous fluorescent light and halide lamps will produce sufficient light if
supplied with effective reflectors, but in deep aquaria (more than 20
inches) is very difficult to offer enough light to small light demanding
foreground plants. Based on known experiments, I suggest commencing CO2
addition before any other action is taken! I believe that even at very
modest light intensities you will experience a conspicuous change in plant
performance in your aquarium. The exact amount CO2 may always be discussed
but concentrations from 10-15ppm will only improve plant growth. You will
probably see that plants, which were barely able to survive before now
thrive in the presence of CO2. These conclusions were derived from work
conducted by Ole Pedersen, Claus Christensen, and Troels Andersen.
- Basics of DIY CO2 Systems
- Injection of CO2 into a planted aquarium can be accomplished in several
ways. There are commercial products available like the tablets available
form Bioplast and other manufacturers that use tablets that fizz like
Alka-Seltzer, and metabolite products like Seachem Excel. While these
provide carbon sources for plants, they do not provide a continuous
injection of CO2 into the aquarium. Another method is a pressurized CO2
system. This is comprised of a tank of compressed CO2 gas, a regulator, and
needle valve. While this is probably the best method available, it can be
cost prohibitive. A nice compromise is the DIY system.
- The first step is creating a CO2 generator, a renewable source of carbon
dioxide. There many ways to generate carbon dioxide gas, but the simplest
and safest method is a yeast generator. Yeast consumes sugar and one of the
byproducts of this is CO2. How yeast does this depends upon the environment
the yeast and sugar is placed in. The most common method is to place yeast
and sugar in a solution with water. This process is known as fermentation.
- Next, you have to be able to collect the CO2 and deliver it to the water
in the tank. The yeast/sugar solution is placed in an airtight container,
which has a fitting that allows a tube to be connected. This tube is then
run to meet the water in some way.
- At this point some efficient manner is needed to inject and dissolve the
CO2 gas into the water. This can be done by directly bubbling the CO2 gas
into the water, passive contact, diffusion, or forced reaction. These
methods will be discussed in more detail later.
- These are the essential elements of a DIY CO2 system: A CO2 generator,
tubing, and a water injection system.
- Some examples of system designs
- While one can design a system that is very complex, this might defeat the
cost effectiveness that warrants a DIY approach. Most of the designs offered
here are done so as examples, and are designed with cost savings in mind,
while at the same time offering a high degree of good engineering practice
and efficient performance.Since yeast generators supply a limited and varied
quantity of CO2 gas, it is imperative that the designs used are efficient in
their ability to deliver and dissolve whatever CO2 is available over time.
- Basic schematic representation of a well-designed DIY CO2 system is shown
below.
- Yeast Generator
- Probably the cheapest and still the best vessel you can use for a yeast
generator is the two-liter soda bottle. If you can find one of those
four-liter versions, that is even better. There are several factors that
make the soda bottle a good choice. First off, it is designed to hold a
solution of water with dissolved CO2 under pressure. This is important. The
pressure that builds up in a yeast generator can be substantial. I would
venture to say it is not lethal, but it certainly can make quite a mess if
it fails and sprays sugar water and yeast all over your house.
- The cap and how to attach the tubing is another issue that has created
much discussion. Most of these caps from soda bottles are made from
polyethylene. Polyethylene does not readily bond with most glue. So gluing
the tubing in place is not desirable. Leaks will occur, especially at the
bond joint. Furthermore, since we're dealing with gasses, the seal must be
airtight. The best all around solution is some mechanical means to attach
tubing. Some type of bulkhead fitting is needed.
- Gas Delivery (tubing)
- Getting the gas to the tank water is the next consideration. Tubing should
be selected based upon several factors. One is pressure retention, or the
ability of tubing to retain its shape under pressure. As tubing is put under
pressure, it should not expand in relation to its diameter. Also the tubing
will need to be inert; meaning not break down over time due to chemical
reaction with the CO2 gas internally or the air or water externally. This
pretty much eliminates standard airline tubing used for fish tank aeration.
Another consideration is flexibility.
- A good candidate for this application is silicon tubing. It does not react
with CO2 as quickly, has good pressure retention characteristics and is very
flexible. There is also special tubing designed specifically for carrying
CO2 gas, and I would encourage spending the few extra dollars needed to use
this. But silicon tubing will last for several years, and is in keeping with
the cost savings approach DIY implies.
- It is also important that water is not allowed to run back down the line
by suction or siphoning. This problem is easily remedied with the use of a
check valve. Many check valves are available commercially. Several factors
should be considered when selecting one. I would avoid choosing one made
from metals. The caustic nature of CO2 gas, the high water vapor content of
the gas (which usually contain carbonic acid), will cause a metal check
valve to fail. Therefore it is important to choose a plastic valve or one
designed specifically for CO2 applications. In addition, for the same
reasons, I recommend avoiding the use of any metal components in the entire
system. In pressurized tank systems, there is generally no liquids, or
solids for that matter, to foul or corrode metal components. So the use of
metal components is common in these systems. The same should not be assumed
on a yeast based DIY system.
- Getting the gas dissolved in the water
- This is a topic that has received much attention on message boards,
mailing list servers, and newsgroups over the years. And I think rightfully
so! Many methods have been described on what the best way to dissolve the
CO2 gas into the tank water. This is the critical point in determining the
effectiveness of a DIY system and the reason why many feel that their
experience with DIY systems was a bad one. Since the amount of CO2 available
in a yeast system is limited by biological production, it is important to
get most, if not all, the CO2 produced dissolved into the water. Skimp here,
and you have wasted your time, not to mention CO2 gas.
- The simplest, and least effective, method is to run the tube into the tank
and simply let the gas bubble into the tank, or through an air stone. I do
not recommend this method at all. Since most of the CO2 gas simply rises to
the surface and is lost.
- Next, many have suggested placing this tube at the inlet of a canister
filter and allowing the impeller to munch up the gas. While it is effective
in dissolving the gas, I do not like this method either, for two reasons.
First, the CO2 bubbles can produce cavitations of the impellor, which could
cause it to vibrate, making noise and possibly damage the mechanism. Second,
some of the components in the impellor use rubber fittings, which could be
broken down over time by the high concentrations of CO2 gas and carbonic
acids present.
 A
better but slower method is the use of what is called a CO2 bell. Simply
put, this is a hemispherical shaped vessel of some kind, inverted and the
CO2 is allowed to fill up inside. The contact area of the gas is increased
and passive diffusion of the gas is increased. The drawback of this is if
the surface area is not high enough, so that diffusion rate exceeds gas
production, the bell will fill with gas and any additional bubbles will run
out the side and travel up to the surface and be lost. While this is a draw
back, many aquarists have had reasonable success using this method of gas
diffusion. These are also very simple to construct. Many have been
constructed from cutting off the tops of one-liter soda bottles, petri
dishes, cups, or any hemispherical shaped object. I would recommend using a
material or object that is transparent, to allow for easy viewing.- Another method is a diffuser.
 Two
versions of diffusers exist. One is device that increases the time the
bubble is in contact with the water. Usually by presenting the bubble with a
long spiral course it has to travel. In the image to the right is one
example of this type of spiral diffusion method, the Econo Aqualine 500
available from AquaBotanic, and others. The manufacturer claims, "The
special construction allows a very high CO2 diffusion rate and automatically
removes any false gasses. The reactor is sufficient for an aquarium up to
125 Gallons". This unit is mounted on the inside of the aquarium.
- Another diffuser type is a glass diffuser. This is a device that increases
the surface area of the CO2 gas by reducing the size of the bubbles
substantially. This is a proven method and can be very effective in allowing
all of your CO2 gas to be
dissolved. In the image to the left is version of this type of diffuser made
by Aqua Design Amano Nature Aquarium Goods, the company led by the legendary
aquatic artist Takashi Amano. The gas is fed into the tube at the rear,
brought down to the bottom and forced against the glass diffuser plate (the
black line running in the middle). This plate has thousands of pores which
the gas passes through, and once it has done this, the bubbles released
through the top of the unit are extremely tiny. This all glass unit is
probably the very best of its kind, and also very expensive since it is
handmade in Japan. Other manufacturers make similar products. The only
drawback of this method is that the plate, usually made of sintered glass,
can clog and may need regular maintenance. Other than that singular
drawback, this is a proven method of diffusion. The drawbacks of both
versions is that their mechanical sophistication do not allow themselves to
be easily homemade, and commercially produced products would have to be
purchased. There are many commercially available choices, in a wide range of
prices, so finding one that works in your budget would not be to difficult,
if you decided on going this route.
- The best method, in my opinion, is the use of a forced reactor.
 A
forced reactor is one that can bring a large quantity of water to the gas.
The previous methods are passive in this respect. In other words if
circulation of the surrounding water is poor, then the diffusion may slow
down due to super-saturation of the water immediately around the diffuser.
By forcing mass quantities of water to meet the gas, via a pump, and mixing
it thoroughly the gas is forced into the water more quickly, and then
circulated. In general a forced reactor is comprised simply of a water pump
and a reaction chamber. Within the reaction chamber there is some course
media to help churn up the gas and water, and increase contact time, as well
as preventing bubbles of gas from escaping. This simplicity of design also
lends itself very well to the DIY concept. The image to the right shows one
example of a DIY Forced Reactor. It is simply comprised of a powerhead with
prefilter, and gravel cleaning tube, a course filter pad, and an airstone.
The cost to build this, if you where to buy all the parts, is under $35US.
More details on this reactor, and other construction projects, will be given
at the end of this article.
- Additional Concepts and Designs
- Since we are dealing with solids, liquids and gasses under pressure, it
may also be a good idea to incorporate some features into a DIY system that
improves both the reliability and safety. Emergency pressure release valves
and anti-clogging devices can be designed, built and utilized in that end.
The construction section of this article details some additional concepts
and designs in these areas.
- More than you need to know about yeast.
- Yeastie the Beastie!
- Yeast is the primary ingredient in our DIY CO2 generators. Common baker
yeasts are adequate for the needs of CO2 generators. But of course, I have
to delve into the esoteric side of things. Yeast is a living organism and
optimal living conditions give it the best opportunity to do what we need it
to do, I had to touch upon this in this text. Also knowing there are as many
strains of yeast as there are different algae, I have to touch on that also.
It is also good to understand the biological processes involved here, and I
will discuss this firstly.
- Theodor Schwann (1810-1882) named the yeast cells "Zuckerpilz"
("sugar fungus"), which later became Saccharomyces, the genus that
most yeast belongs to. Yeasts, that belong to the kingdom Fungi, are
classified as belonging to either of two major types: budding yeasts, named
so because of the buds formed at the cell divisions, and fission yeasts that
are rod-shaped and grow by elongation at their ends. Most yeast used is of
the budding type. Although easily grown in culture media, each S. cerevisiae
cell (the most common species for our purposes here) has a limited number of
buddings of around 20. However, in a given culture only about half of the
cells will have given rise to new cells, and only rarely does a cell give
rise to as much as 20 new cells. Poisoning, mutations and heat are other
factors that affect the viability of yeasts. Towards the end of fermentation
many yeasts aggregate into clumps, a phenomenon known as flocculation. The
process of flocculation is not completely understood, but it is believed to
be mediated by bivalent ions such magnesium, calcium or manganese ions.
- Yeasts are probably the most researched organisms in microbiology. Entire
scientific communities and disciplines have evolved surrounding this simple,
single-cell fungi. If you want to blow your mind out one day, check out this
link below. It is a list of researchers, their associated laboratories, and
their research papers on the singular species Saccharomyces cerevisiae. This
yeast has the distinction of not only being the one we generally use for our
CO2 generators, but also being the first organism to have its entire genome
(DNA) completely mapped in 1996.
- Yeast
Labs and Research
- This is only for the brave of heart! Good luck! A more pragmatic
description of the biology of yeast is given below.
- BIOLOGY
- YEAST: A living organism formed of only one cell. Each cell, which is a
living being, of a spherical or ovoid form, is nothing but a tiny and
simplified fungus the size of which does not exceed 6 to 8 thousandth of
millimeter.
- Yeast, like any living organism, lives thanks to the presence of oxygen (aerobiosis);
but it also has the remarkable ability of being adaptable to an environment
deprived of air (anaerobiosis).
- To cope with its expenditure of energy, it can use different carbon
substrates, mainly sugars:
- Glucose is the best favored food of Saccharomyces cerevisiae;
- Saccharose is immediately transformed into glucose and
fructose by an enzyme which yeast has released;
- Maltose is the main endogenous substrate of French bread
fermentation; it gets into the yeast cell thanks to a specific permease to
be split afterwards into two molecules of glucose by maltase.
- Many other sugars are also utilized.
- An interesting scientific work by Vern J. Elliot shows the utilization of
sugars by yeast, and yields some insight into this question. If you look at
the chart below you will see growth rates of yeast over time when fed by
different sugars.
- Just to understand the chart, the reference of the test is as follows,
(for you technically oriented folks out there) "... Plates (growth
samples) were incubated at 28?C and growth was determined at time zero and
at approximately 24-h intervals by measuring absorbance at 630 nm with a
microplate reader (Model ELx800UV, Bio-Tek Instruments, Winooski,
VT)...".
-
- While this experiment tested some 250 different strains of yeast, and the
chart above shows the strain labeled "isolate 59", a brief
examination of the published paper shows that nearly all the strains showed
similar results in terms of sucrose providing the highest growth rates. It
can be reasoned that the yeast strains we use in our CO2 systems would have
similar results.
- So what does this mean. Essentially, using less yeast and more cane sugar
(sucrose), and allowing the yeast to grow and multiply will assure a longer
lasting CO2 mixture. Conversely, CO2 quantity measured over time is another
issue more related to use of specific mutant strains of yeast than type of
sugar. Longevity of the yeast culture, due to toxic death, is also not
related to type of sugar, but to alcohol levels. Acids play a much lesser
role in this respect than popular belief, by the way. (More on this later).
So, use of sucrose seems to be a better choice, other factors not
withstanding, than other sugars.
- The conditions of oxygenation of the environment generate two types of
metabolism:
- In AEROBIOSIS
When yeast is in presence of air, it produces, from sugar and oxygen,
carbon dioxide, water and a great amount of energy. It is the metabolic
process of respiration. In these conditions the oxidation of glucose is
complete:
Glucose + Oxygen ?> Carbon dioxide + Water + Energy
All the biochemical energy potentially contained in glucose is freed.
Thanks to this energy, yeast ensures its life. But it can also use it to
synthesize organically, that is to say start its growth and multiply. It
will then have to find other nutritive elements in its environment, mainly
nitrogen.
- In ANAEROBIOSIS
When there is no oxygen available, yeast can nevertheless use sugars to
produce the energy it needs to be maintained in life. Pasteur defined this
metabolic process as being the fermentation process. Sugars are transformed
into carbon dioxide and alcohol. The glucose oxidation is incomplete:
Glucose ?> Carbon dioxide + Alcohol + Energy
The alcohol, which has been formed, still contains a great amount of
energy. This constitutes only a part of the biochemical energy potentially
present in glucose that was freed (about 20 times less than for
respiration). It ensures a minimum level but doesnot enable yeast to
multiply rapidly.
- ANAEROBIOSIS is the process we use in our CO2 generators, although
AEROBIOSIS would be preferred. Aerobiosis is preferred because it produces
less alcohol, which is toxic to yeast at elevated relative level. But
aerobiosis is also impractical for reasons you will see later.
- "God is Good" is the name which yeast was given in the early
days of fermentation. This is prior to the time when Louis Pasteur, in the
mid 1800's, discovered that, in fact there was actually a single cell
microscopic organism responsible for the conversion of fermentable barley
malt sugars into alcohol, carbon dioxide, and flavor compounds.
- As described by Gay-Lussac at the beginning of the nineteenth century, the
chemical reaction of fermentation is as follows;
C6H12O6 + Saccharomyces cerevisiae =
2C2H5OH +2CO2
(Sugar plus yeast yields alcohol and carbon dioxide) |
- The tail end of the formula is the thing we're looking for CO2!!!
- Beverages including wine, fermented milk products, and mead from honey are
some examples of what developed from spontaneous fermentation, which is now
understood and managed in a scientific manner. Many of these organisms were
discovered more by chance, than by design. Other types of yeast and bacteria
are also utilized in various styles of beer and brewing beer like beverages.
- The following is a description of the many strains of yeast that are
available for CO2 generation. Some are commonly available and inexpensive;
some are harder to get and more expensive. The advantages and disadvantages
of each type are explained.
- Bakers Yeast
- Bakers yeast (or Dutch Process yeast) is widely available at nearly every
supermarket. It is dried active yeast. I like the term "mummy
yeast" because it does seem to "rise" from the dead. Ouch!
Bad pun, I know! Most of us know bakers yeast, popularized by companies like
Fleishmann's. They manufacture little packets or you can buy 4oz. jars. It
comes in several variations. Regular bakers yeast in 7-gram packets is by
far the most common. Lately a new form known as "Bread Machine"
yeast has appeared. This yeast is more tolerant of higher temperatures found
when using these new automated bread machine thingies. Both work well in our
application. The bread machine yeasts are available in 4 oz jars, which are
more economical. Here are some detailed specifics on these types of yeast:
- The following information is typical for each type of bakers yeast, but
may vary somewhat according to product and company:
Compressed Yeast (also called cake, wet, and fresh yeast)
Fleischmann's compressed yeast is available in supermarkets in 0.6 oz cakes,
and Red Star compressed yeast is available in some supermarkets in 2 oz. cakes.
It is found in the dairy or deli case. Compressed yeast is available to
commercial bakers from a variety of companies in 1 and 2 pound packets.
Compressed yeast has approximately 30% solids and 70% moisture content. It is
highly perishable and must be stored at a uniformly low temperature (about 40?
F) to prevent excessive loss of activity or gassing. Compressed yeast generally
has a shelf life of approximately two weeks from its make or packaging date when
kept at 73.3? F. (23?C)
- At 32?-42? F. (0? - 5.5? C) compressed yeast loses approximately 10%
of its gassing power over a 4-week period. At 45? F (7.2? C) yeast will
lose 3-4% of its activity per week. At 95? F (35? C), one half of the
gassing power is lost in 3-4 days. Once yeast starts to deteriorate or lose
its fermentative activity, it does so quickly, losing almost all of its
activity (autolysis) by the third week. It has, however, been shown that
compressed yeast can be successfully stored for two months at 30? F. (-1?
C). When this is done, good CO2 production can be made from yeast stored for
two, but not three, months.
- To use compressed yeast, soften it in tepid water.
-
Active Dry Yeast
- Fleischmann, Red Star, and SAF active dry yeast are available in
supermarkets in ? oz (7 g) packets and/or 4 oz (113.4 g) jars. Active dry
yeast is available to commercial bakers from a variety of companies in 1 and
2 pound, and 500 g packets. It also is available in these sizes to consumers
at warehouse or club stores, and via mail order. Active dry yeast has
approximately 92.0% solids and 8.0% moisture content. It is advisable to
store active dry yeast in a cool, dry place that does not exceed 80?F.
- The shelf life of "active dry yeast" stored at room temperature
is approximately 2 years from its make date. Once opened, active dry yeast
is best stored in an airtight container in the back of the refrigerator,
where it will retain its activity for approximately 4 months. To rehydrate
active dry yeast, blend one-part yeast with four parts lukewarm water, wait
10 minutes, and stir. Depending upon the particular product and company,
lukewarm water ranges from 90?-115? F. Temperatures lower than 90? F and
higher than 115? F should be strictly avoided.
-
Instant Active Dry Yeast
Fleischmann, Red Star, and SAF instant active dry yeast is available in
supermarkets in ? oz (7 g) packets and/or 4 oz (113.4 g) jars. The
Fleischmann product is marketed as RapidRise, the Red Star product is
marketed as QUICK.RISE, and the SAF product is marketed as Gourmet Perfect
Rise. Fleischmann also markets an instant active dry yeast named Bread
Machine Yeast. Instant active dry yeast is available to commercial bakers in
1 and 2 pound, and 500 g packets. It also is available in these sizes to
consumers at warehouse or club stores, and via mail order. Instant active
dry yeast has 96.0% solids and 4.0% moisture content. It is advisable to
store instant active dry yeast in a cool, dry place that does not exceed 80?
F.
The shelf life of instant yeast stored at room temperature is
approximately 2 years from its make date. Once opened, instant active dry
yeast can be stored in an airtight container in the back of the
refrigerator, where it will retain its activity for approximately 4 months.
To rehydrate instant active dry yeast, blend one-part yeast with five parts
lukewarm water, wait 10 minutes, and stir.
- It is worth noting that there is disagreement among the yeast companies as
to whether or not active dry and instant active dry yeast should be frozen,
and if in doing so the shelf life of the yeast is prolonged. The most
convincing argument against freezing is that under normal conditions, there
are temperature fluctuations in freezer units caused both by repeated
opening and closing of the freezer door and, in contemporary freezer models,
by the self-defrosting (freeze and thaw) cycle. These temperature
fluctuations can cause damage to the yeast cell structure.
- One topic upon which there is agreement is that if active dry or instant
active dry yeast has been refrigerated, and is going to be rehydrated in
lukewarm water, it is best to allow the portion of yeast to be used to come
to room temperature prior to blending it with the lukewarm water. Otherwise,
temperature shock might damage the yeast cells.
- Unlike compressed yeast, which disperses in cold water without any
problems, the temperature of the water during rehydration is important when
working with dry yeast. When yeast is dried, the cell membrane becomes more
porous. During rehydration, the membrane recovers. However, in the process
of rehydration, some cell constituents are dissolved in the water used. The
optimum water temperature for cell membrane restoration is 104? F. Warm
water is effective in this process, because it leads to more rapid cell
membrane recovery. Cold water impedes this process, because it slows
membrane recovery and allows more cell constituents to leach out during the
reconstitution process. The effect is not that great between 70? and 100?
F, but at lower temperatures approximately one-quarter to one-half of
soluble yeast cell constituents can be lost. This leaching action effects
yeast activity in the following manner: Most yeast enzymes remain, but the
soluble chemicals are depleted, and it is these chemicals that promote
enzyme activity.
- Brewing Yeast
- These are specific strains of yeast that are used in the brewing of beer.
There is a wide variety of brewers yeasts bred specifically for different
types of beer, and is what makes most brands taste different by the way.
It's not the "?clear mountain water" or "?the loving
hands of the brew master". It's the bugs they put in it! Use a
different bug; get a different tasting lager or ale. Saccharomyces
cerevisiae, and Saccharomyces uvarum are the genus and species of ale, and
lager yeast respectively. These are the primary types of yeast cultures,
which produce most of the world's beers. The Ale yeast is a specialized
strain of S. cerevisiae, which adapts better to higher alcohol levels.
- Most of these are live cultures in liquid form, and do not require the
rehydration process used with dry yeasts.
- Wine or Champagne Yeast
- These are very specialized yeast strains that do different things, like
soften the wine's acidity or absorb tannins lightly. This is accomplished by
the release of enzymes specific to this strain of S. cerevisiae. In
addition, they also can ferment at a wide range of temperatures and can
tolerate the highest alcohol and acid levels, which is toxic to most yeast.
This is an important point for our application.
- Another benefit side effect is that this yeast has a tendency of settling
towards the bottom of a culture, or it is said to be a bottom flocculent.
Bakers and Ale yeasts are top flocculants, which is that gooey, tan head on
the top the sugar water you see when using bakers yeast. Champagne yeasts
usually do not have this build up of yeast at the surface. Therefore they
can help reduce a common problem with DIY CO2 systems, the clogging of the
airlines, and raw yeast getting pumped into the tank.
- Some of the best yeasts, discovered in my testing for our application, are
sold under the brand names "Pasteur Champagne" and "Eau de
Vie", from Wyeast Labs, Inc. in Mt. Hood, Oregon.
- Again, as with brewers yeast, most of these are sold as live cultures in
liquid form, and do not require the rehydration process used with dry
yeasts.
- What are the advantages of the more esoteric yeast for DIY CO2?
- Right off, I will say that you can certainly use the common bakers yeast
with great success. It is more than adequate. But there are certain factors
where you may want to optimize the performance of your system.
- One downright frustrating thing about DIY CO2 is the maintenance and
replenishment of the mixture. You have to change your mixture every 7-14
days, depending on how well your particular formula works. Fourteen days
seems to be the limit for most yeast mixtures in a two-liter bottle when
using bakers yeast. This is due to the fact that the alcohol levels reach a
point where it kills the yeast cells, even if it hasn't used up all the
sugar. The general consensus has been that it is the rise in acid levels
that kills off the yeast. But this is probably not true. One way that has
been proposed is to add baking powder as a buffer to the mixture to regulate
the acids, but this does little to effect the alcohol levels. Oddly it is
not the acids that are problematic. Yeast can generally deal with acidic
levels to a point, as you will see below.
-
Yeast Tolerance to Acidity
Yeast exhibits a considerable tolerance to extremes of pH, being able to
maintain an active fermentation in a 5% glucose solution in the pH range of
2.4 to 7.4, but ceasing activity at pH 2.0 or pH 8.0. For optimum results,
good practice dictates that the pH of the fermenting medium be maintained
within the range of about 4.0 to 6. A drop of more than 50% in fermentative
activity has been observed at pH 3.5. More gradual declines in yeast
activity were encountered at higher pH levels, with measurable effects
showing up at pH values over 6.0.
The explanation for the yeast's ability to maintain a relatively constant
activity over a 100-fold change in hydrogen ion concentration (pH 4 to 6) is
found in the fact that the pH of the cell interior of the yeast remains
quite constant at about pH 5.8, regardless of any relatively wide pH
variations in the fermenting medium. The enzymes involved in fermentation
thus operate in an optimum pH environment within the yeast cell that is
largely unaffected by external changes in pH.
- Conversely, sodium ions are also toxic to yeast, so once the sodium
biphosphate has been broken down by the acids, the free sodium ions tend to
kill off more yeast cells. So this method is only a transparent fix to the
yeast kill-off. The logical alternative is to find strains of yeast more
resistant to high alcohol levels, since alcohol appears to be the true
killer. The apparent regulation by buffering with baking powder is probably
due to the issue of sodium slowing the reproduction process, thereby slowing
the consumption of sugar by limiting the population of living yeast cells.
While this extend the life of the mixture, it also reduces the CO2 output
over the lifespan of the mixture. This is a result of reduced, or at least
controlled, yeast cell population.
- Brewers yeast is one step in the right direction. Strains of Saccharomyces
cerevisiae brewers yeast, commonly referred as Ale Yeast, is a good choice
for this. It is more tolerant to higher alcohol levels and should provide a
longer lasting mixture; usually by about 4-6 days longer than the bakers
yeast strain. It is also seems to be more tolerant of sodium. Using Ale
Yeast in your mixture can yield a longer lasting mixture.
- Champagne Yeast is tolerant of the highest alcohol levels, and wider
temperature ranges. Another side effect is that its metabolism seems to be
in hyper-speed, producing nearly twice as much CO2 as other strains. It also
ferments well at average room temperatures. This makes it the perfect yeast
strain (and the most expensive) for our applications. I have had mixtures
with this strain, very carefully prepared aseptically, last strongly for
nearly 24 days.
- Now for the downside. Costs are very high with these esoteric yeasts. The
cost is nearly 3-5 times more expensive as common bakers yeast. Also, these
yeasts work better if inoculated into your sugar water when they are alive,
which is the form they are purchased in. This makes storing them difficult.
The manufacturers makes these available to home vintner's, and are prepared
in much larger quantities than we would use. Anything left over last only
for a very short period, and is difficult to store and keep viable.
- Finally, it should be noted that there is also an inverse relation between
the amount of yeast and fermentation time. Thus, a reduction in the amount
of yeast will result in longer fermentation times, while an increase in the
amount of yeast will shorten them. We'll talk about this more in the section
on mixtures.
- Yeast is hardy, yeast is intolerant.
- Now that's an oxymoron if I ever saw one. But that's the nature of the
yeast. It can withstand drying, pounding, skimming, centrifugal forces,
replicates itself easily; yet in the wrong situation it will crash faster
than a CO2 injected tank with a 1dkH when the mixture runs out. oops?got
ahead of myself there.
- One of the most important issues to remember when using yeast in
fermentation is cleanliness. Yeast does not compete well against bacteria,
so it is important to keep things as close to sterile as possible. One
excellent and simple way to deal with this is as follows.
- Note of Caution: Be very careful with this, since very bad burns can be
had here.
- Thoroughly rinse out your two-liter bottle with hot water; use no soap or
detergent. Keep an extra bottle cap handy. Boil the water you plan to use,
and place this extra cap in the water to sterilize it. Pour the boiling
water (use a funnel) into your two-liter bottle. While it is still ripping
hot, add your sugar, and use the cap you boiled clean, and cap the bottle
tightly. Shake well until most of the sugar dissolves. This sterilizes the
bottle, water, and the sugar. This iswhat they call an aseptic preparation.
Do not uncap this until you let the water cool to room temperature and are
ready to add the yeast.
- If you plan to use dry yeast you should activate the culture first. As
discussed previously, yeast needs to start in an aerobic environment first,
so it can then readily adapt to the anaerobic conditions in our little
fermentation factory. Many folks who omit this step believe they are
creating this situation with just the action of pouring the mixture into
their bottle. But they also do not realize that much of the yeast they use
dies, because many of the yeast cells could not complete the aerobic phase
of its life before the conditions change to anaerobic. This step insures all
the yeast is already aerobically active and working before it is placed in
the generator. The time it takes for the generator to begin producing
pressurized CO2 is significantly reduced by this following step. These
yeasts also need to be rehydrated properly, as also previously mentioned, so
as to not damage the yeast cell walls.
- I take my measure of yeast, add a small quantity of tepid water, 100?-115?F,
(not hot), and stir it up in a little cup with a fork. Stir the mixture
until the yeast in no longer in clumps, but instead a smooth creamy tan
liquid. Now here's the part everyone forgets, add a few pinches of sugar and
vigorously mix the yeast liquid up making lots of bubbles. You want to get
oxygen in there to get the yeast going. Once this is done, let the mixture
stand for about ten minutes. Then take your funnel in hand, open the aseptic
bottle you prepared, and pour in your yeast culture.
- Now granted this isn't a perfectly sterile method, but by reducing the
chances of bacteria getting in on the outset, the yeast mixture will prevail
quicker and last that much longer.
- More information about specific mixtures, formulas, and capacities of
systems will be given in the next section of this article.
- Authors Final Notes on Yeast
- In preparing this article, I have conductedresearch into yeast and dove
headfirst into the scientific data available from researchers. To date I
have not been able find data on any specific strain mutated for its ability
to produce CO2 gas exclusively, while it appears there has been some strains
developed. Generally, mutant strains of yeast are selectively bred for
controlled production of by-products like alcohol and carbon dioxide. Can
yeasts be improved for our purposes? Most likely work will continue on this
process for as long as there are chemists, and geneticists interested in
yeasts. One of the more interesting new research areas in this domain is the
work on recombinant-DNA technology as it pertains to the development of
newer yeast strains. This work has led to changes in formulation,
ingredients and processing conditions. Some of this work has led to new
strains of yeast that are more resistant to stress, produce more proteins,
and more carbon dioxide.
- Some discussion exists on the genes in the HTX group and the role they
play in the cell utilizing glucose in various stages of it life. In the
yeast Saccharomyces cerevisiae, the Snf1/AMP-activated protein kinese family
is particularly important for the response to glucose deprivation, and this
kinase regulates genomic transcription, metabolic activity, and
developmental processes such as invasive growth. These genetic research
results show, in effect, the potential for a mutant strain that is longer
lasting since it could be designed to utilize less glucose, or require less
glucose to produce CO2 in useful quantities for our purposes here. If there
is any other specific scientific data on this, I would be interested in
seeing it.
- Guidelines for Mixtures and Capacities
- It is important to understand that the yeast/sugar/water mixture is not a
precise science. You will have to experiment to find what works best for
your situation. I will give some suggestions in this section on formula's
based upon the scientific data presented above and my own personal
experience.
- Mixture Formulas
- For two-liter bottles:
- 2 cups water
- 2 cups Sucrose (cane sugar)
- ? teaspoon Fleischmann's Active Dry Yeast
- ? cup tepid (ideally 104?F) water
The yeast should rehydrated first in the tepid water. The aseptic method
mentioned previously should be used.
- This is the easiest formula, using the most widely available ingredients.
This mixture can last up to approximately 16 days, if the aseptic method is
used.
- An improved formula is:
- 1? cups of water
- 2? cups Sucrose
- ? teaspoon Wyeast Labs, Eau de Vie vintners yeast
The aseptic method mentioned previously should be used.
- This is a more costly mixture. Since this yeast is a liquid live yeast,
(referred to as pitchable) it does not need to be rehydrated. This yeast is
more tolerant to higher alcohol levels, therefore this mixture can last up
to approximately 22 days. It also has a more consistent output of gas over
time.
- Tips on Mixtures
- You should experiment on your mixtures. Everybody has different water,
with its own unique chemistry. And this influences the performance of your
mixture. So try slight modifications of the yeast/sugar/water ratios till
you find what lasts the longest for your situation.
- There is evidence that yeast mixtures last longer if you decrease the
amount of yeast, and conversely last shorter periods if more yeast is used.
Lower yeast also means less CO2 produced per minute, but produce more
consistently over time. Higher yeast levels will cause an initial higher
burst of CO2 production with a gradually declining production over time.
Keep this in mind while experimenting.
- There also has been some discussion on adding other nutrients to the
mixture to help the yeast grow and multiply. This is an area I have not
researched directly, but may be of interest. Nitrogen seems to be a nutrient
that yeast utilizes. Unfortunately the research I have gleaned showed that
nitrogen is used by yeast only when it is in an aerobic environment, not the
anaerobic environment we are putting it in. I have not seen any direct
research that showed any nutrient other than sugars are used by yeast in
anaerobiosis.
- Speaking of aerobiosis, as shown before this reaction only produces CO2
and water as by-products. Alcohol is not produced. So why not just produce
an aerobic environment? This would involve injecting oxygen (O2) into the
mixture chamber. Now one could aerate the mixture to do this, but of course
this would be sent out into the system that is supposed to dissolve only CO2
gas. The problem is obviously a matter of either injecting an air mixture
with elevated CO2 levels into your tank, or choosing a pure CO2 gas to be
dissolved. The latter is what is preferred, and in fact essential for a CO2
system to work from a practical concern. So unfortunately we still will have
to deal with alcohol as a by-product, and deal with it accordingly.
- System Capacities
- A good CO2 system will provide enough gas to supply a given amount of
water to reach the idealized level of 15ppm of dissolved CO2. As a rule of
thumb, each two-liter bottle will provide enough gas for up to 30 gallons of
tank water, assuming you use an efficient method of mixing the gas and tank
water.
- It is important to remember when using CO2 injection in a freshwater
planted aquarium that doing so reduces the pH in the water. Some of the CO2
dissociates and forms Carbonic Acid. This results in a lowering of pH due to
the addition, or more accurately put, the creation of acids in the tank
water. To prevent wide fluctuations in pH over the life of your mixtures it
is important to make sure the buffering capacity of your tank is high
enough. This is determined by measuring the carbonate hardness of your tank
water. This is referred to as your waters kH. A good kH for most planted
tanks is around 6dkH. This will ensure your pH doesn't swing to abruptly
over the life span of your mixture.
- Interestingly, you can use this relationship of carbonate hardness and pH
to determine you CO2 level in your tank. If you have fresh and accurate test
kits, one for pH and another for kH, you can use the chart below to
determine your CO2 levels.
-
Chart derived by George Booth, rendered by Jeff Dietsch
- Construction Projects
- Okay, here's the fun part. Actually making a DIY CO2 System of your own.
On average, a DIY CO2 system for a 55 gallon tank, like the one depicted at
the beginning of this article, would cost about $50 to make, complete! And
that includes the soda. Remember, that's probably about a quarter of the
price of a complete pressurized system with a diffuser of some kind. While
the pressurized system is the best way to accomplish CO2 injection, the DIY
method will provide very excellent performance, costs substantially less
money, and can be even fun to build if you're handy. There is nothing like
the pride and satisfaction of knowing that you " Did It Yourself"!
- The Perfect Two-Liter Bottle Generator
- While using a two-liter soda bottle for a generator is not a new idea, one
of the downfalls of most attempts has been in connecting the tubing to the
bottle cap. Most caps are manufactured from a material known as
polyethylene. It is used because it wears well, is resistant to bacterial
growth, and is resistant to acids. It also has a excellent ability to deal
with pressure. In addition to being a good candidate for a soda bottle cap,
these same characteristics make it ideal for our application. But
unfortunately, polyethylene is also difficult to bond with most adhesives.
- Most instructions for using soda bottles for generators advise drilling a
small hole, and gluing the airline in place. This has been the weak link in
most DIY generators. The poor bonding capabilities of the cap always lead to
seal failure, and consequent leaks. An improved way of dealing with this
would be to have some type of mechanical seal, and a bulkhead type fitting
for the tubing to connect to. This would be better engineering practice.
Above is a diagram showing the completed two-liter bottle generator with the
bulkhead fitting in place.
- One of my other hobbies is RC airplanes, specifically jets! This little
device is a nylon bulkhead fitting for engine fuel. It is designed for use
with silicon tubing just like the type we use with CO2 systems. It screws in
tightly into the hole in the two-liter bottle cap, makes an airtight
mechanical seal, and makes removing the tubing from the bottle a breeze when
you change your mixture.
- Here is a link to a place where you can purchase this online:
- Tower
Hobbies
- It's manufactured by Fourmost Products, Oregon, and sells for around
$3.75US. If you have a very good hobby shop nearby, you may be able to get
it there. You get two fittings in the package. I love these things; they
made doing mixture changes and worn cap replacement a breeze!
- Over Tolerance Pressure Release and Prevention Systems
-
- In yeast generator systems a common frustration is clogging of the air
lines due to flocculated yeast. Sometimes yeast will get trapped in the air
lines and pressure can build up to the point where you have an explosive
situation. It is not uncommon for the cap to blow off, one of the airlines
blowing off, or even one of the generator bottles failing. When this occurs,
the usual result is smelly, sticky yeast solution gets blow great distances
around your home. Yuck!
- One solution is a simple Pressure Release System. Essentially, all this is
some form of plug that will blow off when a certain amount of over pressure
is developed in the system. One type of this release valve is shown in the
image to the right. This is comprised of a nylon airline tee,
 and
some soft plastic or rubber cap. The part of the tee for the cap must have
its barb carefully sanded off with emery cloth until it is smooth. It must
be sanded down in such a way where the cap fits on snugly so as to not leak,
but also pop off if the pressure builds up high enough. This has to be done
thru careful trial and error. I take a bottle of seltzer, put the special
cap on it for the generator and fit the tee on with the cap and the other
side of the tube blocked or plugged. I then shake the seltzer bottle till
some pressure builds and up and observe the point at which the cap blows
off. It takes some time and patience to make one these work right. If you
sand down too much and the cap is not snug enough it will blow to early, so
you have to then start over with a new tee and test again. The whole process
of making one of these do-hickey's is a little bit tweaky, so if do not have
the patience to sit down and carefully craft one these I would recommend not
doing it. It will, if not made properly, work when you don't want it to and
cause more trouble. This unit should be placed between what runs into the
tank and a Gas Separator. Which lead me to the following...
- Another means by which you can eliminate or reduce yeast build up in the
airlines is by using a Mechanical Gas Separator. Basically, this is a bottle
with an input and output fitting. The idea is to use this vessel to separate
the gas from solids and liquids using gravity. This therefore prevents
solids from making their way up the tubing and clogging at some point. The
image below this paragraph depicts an example of a separator made from (you
got it) a 16oz. soda bottle. It is attached with nylon tie-wraps to the side
of a two-liter yeast generator bottle. Once again our special bulkhead
fittings are used, only this time two are placed on the cap. Inside the
bottle, a length of rigid air line tubing is placed onto the inside of one
of fittings. This is the input of the separator. The other fitting remains
unmodified. This is the output of the separator. The concept works like
this; gas, liquids and solids come from the yeast generator and enter the
separator through the input and into the bottle thru the rigid tubing. Any
liquids and solids will fall, due to gravity, to the bottom of the separator
bottle. The gas, not being effected by gravity but instead from gas
pressure, continues on through the output fitting and out to your tank. The
rigid tubing serves to provide a larger distance between the input and
output to reduce the chance of blow by of the liquids and solids, if the
pressure release valve blows. This also prevents solid material, like
flocculated yeast cells, from clogging your airlines during normal
operation. For best effectiveness, the separator should be placed as
physically close to the yeast generators as possible.
Using any or both of these safety systems insures improved performance and
reliability of your overall system. These two simple designs, if made properly,
will provide assurance that the most common problems in DIY systems, tube
clogging and high pressure explosive failures, are substantially reduced, if not
eliminated completely. Try them!
- DIY Powered CO2 Forced Reactor
- This section describes a DIY powered CO2 reactor made from parts widely
available at nearly all LFS (local fish store) and online dealers. No
special tools are required since all components push together, with the
single exception of a drill bit. The cost of the entire device is under
$35US complete and has a total count of 8 parts inclusively. The unit also
doubles as a mechanical/biological sponge filter system, and could be the
sole filtration for tanks up to 30 gallons in volume.
- The image to the right shows a drawing of the completed unit. The unit
will work with DIY yeast systems, or the more complex pressurizedCO2 systems
commercially available. The primary purpose of this reactor
is to allow C02 to be thoroughly dissolved into the tank water. This is
accomplished by injecting the CO2 into the reactor, and keeping it contained
in a chamber with a high flow rate of water. This is an active system, which
means it brings water under pressure to the CO? instead of simply allowing
the CO2 to passively meet standing water, as in a diffuser with scintered
glass or a bell. It also is much less prone to clogging like the
aforementioned diffuser. The system prevents CO2 bubbles from escaping the
tank before being dissolved; meaning nearly all the CO2 you inject gets
dissolved.
- By having a large foam pad over the inlet for the powerhead, instead of
the usual inlet basket, the unit doubles as a foam filter. This also prevent
clogging of the pump impeller and keeps the mesh pillow at the bottom of the
reactor chamber clear from debris. If debris was allowed to collect on this
pillow, flow would be impeded and the CO2 would have a difficult time
getting into the reactor due to back pressure in the chamber. A check valve
on the CO? line is therefore a requirement. I have determined that this
foam filter would be sufficient to supply all the filtering needs in a
heavily planted tank, with a moderate fish load of up to 30 gallons. No
other filtration would necessarily be needed.
- The pump is a standard powerhead, a Maxi-Jet
PH 600 manufactured by Aquarium
Systems. This unit sells on the web for about $14 and is used to pump
water into the reactor chamber and as the filter.
 It
delivers a flow rate of about 160gph, which in theory would pump the water
of a 55 gallon tank twice every hour through the reactor chamber. Most of
the Maxi-Jet's supplied accessories are unused except the suction cups used
to attach it to the tank wall. The pump itself will be used unmodified for
this application. The Maxi-Jet 600 PH pump and power head includes an
innovative triple-suction cup mount which is sufficient to hold the entire
reactor in place inside your tank. It is a fully submersible powerhead and
the only items that need to be fed out of the tank will be t
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