# [Wet Thumb Forum]-Understanding DIY CO2 reaction rates



## Gomer (Feb 2, 2004)

I am trying to understand the reaction rates of CO2 production with respect to yeast, sugar and water.

I will list a few scenarios with what "I think" the changes will could be. can someone please comment and clear this up









Initial conditions: 1/4tsp yeast, 2cups water, 1 cup sugar

Change 1: double yeast
Possible Effect 1?: the the CO2 production reaches the same steady state X of CO2 production 2x faster 
Possible Effect 2?: The CO2 production will ALWAYS be 2x faster and you will have to change the solution twice as fast.

Change 2: double the sugar
Possible Effect1: none since the production is limited by the alcohol produced and not by the food available.
Possible Effect2: production is slowed because the solution is too concentrated for effective CO2 production
Possible Effect3: Production rates are the same, but the solution will last 2x longer

Change 3: Double water
Possible Effect1?: none
Possible Effect2?: the rates will be the same, but the alcohol dilution means that the yeast will not be limited by poisoning and will allow to produce C02 for a bit longer

Change 3: Double the sugar and water
Possible Effect1?: same production rate, but have 2x the time before having to change

Change 4: Double all
Possible Effect1?: Production rates double, but all else remains the same.


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## Gomer (Feb 2, 2004)

I am trying to understand the reaction rates of CO2 production with respect to yeast, sugar and water.

I will list a few scenarios with what "I think" the changes will could be. can someone please comment and clear this up









Initial conditions: 1/4tsp yeast, 2cups water, 1 cup sugar

Change 1: double yeast
Possible Effect 1?: the the CO2 production reaches the same steady state X of CO2 production 2x faster 
Possible Effect 2?: The CO2 production will ALWAYS be 2x faster and you will have to change the solution twice as fast.

Change 2: double the sugar
Possible Effect1: none since the production is limited by the alcohol produced and not by the food available.
Possible Effect2: production is slowed because the solution is too concentrated for effective CO2 production
Possible Effect3: Production rates are the same, but the solution will last 2x longer

Change 3: Double water
Possible Effect1?: none
Possible Effect2?: the rates will be the same, but the alcohol dilution means that the yeast will not be limited by poisoning and will allow to produce C02 for a bit longer

Change 3: Double the sugar and water
Possible Effect1?: same production rate, but have 2x the time before having to change

Change 4: Double all
Possible Effect1?: Production rates double, but all else remains the same.


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## 2la (Feb 3, 2003)

I'll take a (blind) stab...

NOTE: All of the following assumes zero-order kinetics in which the amount of sugar far exceeds the amount of yeast (i.e., the amount of yeast is the limiting factor).



> quote:
> 
> Originally posted by Gomer:
> Initial conditions: 1/4tsp yeast, 2cups water, 1 cup sugar
> ...


Effect 2 would be true IF the amount of sugar matches EXACTLY that which is required to produce a lethal alcohol concentration. Effect 1 may also be true but you would have to eliminate confounding factors such as activation time of the yeast, how much of the yeast is exposed to the water and sugar (e.g., if the yeast is doubled, the cells in the center of the clump will take longer to become soaked), etc. All else being equal, though (i.e., assuming that ALL the yeast cells are activated simultaneously and that ALL the yeast cells ferment at the same rate), CO2 production will reach maximum levels (your so-called "steady state") in the same amount of time regardless of how much yeast is used. Your statement of "same steady state X of CO2 production" is a little confusing, however--I'm not quite sure how to interpret it.



> quote:
> 
> Change 2: double the sugar
> Possible Effect1: none since the production is limited by the alcohol produced and not by the food available.
> ...


Effect 1 will predominate, again under the condition that the amount of sugar in the original mixture matches EXACTLY that which is required to produce lethal alcohol levels. But, if the starting amount of sugar used was, say, 1 teaspoon such that the amount of alcohol produced from fermentation would never reach lethal levels, Effect 3 would then predominate.



> quote:
> 
> Change 3: Double water
> Possible Effect1?: none
> Possible Effect2?: the rates will be the same, but the alcohol dilution means that the yeast will not be limited by poisoning and will allow to produce C02 for a bit longer


Honestly, that's hard to say. I've always used much more water than 2 cups. Effect 2 theoretically would be possible if it was known that in the _original_ recipe, lethal alcohol levels were reached EXACTLY at the same time that ALL of the sugar was consumed. That way you'd be controlling strictly for end-fermentation alcohol levels.



> quote:
> 
> Change 3: Double the sugar and water
> Possible Effect1?: same production rate, but have 2x the time before having to change


Yes, again assuming zero-order kinetics.



> quote:
> 
> Change 4: Double all
> Possible Effect1?: Production rates double, but all else remains the same.


Yes, CO2 produced doubles over the same lifespan as the original.

 
(Click for pics)


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## Gomer (Feb 2, 2004)

Thanks for the "blind stab"









I am sure that this needs some empirical work







I was just trying to dig up past people experience. While your answers assume zero order reactions, this need empiricle data to establish ..unfortunately









...mmm...maybe I can do a kinetics study. perhaps I can use the flowmeters in the lab. We are not using them right now


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## Roger Miller (Jun 19, 2004)

My stab isn't entirely blind, as I've tried some of these, I've read a little about yeast and others have experimented and reported the results.



> quote:
> 
> Initial conditions: 1/4tsp yeast, 2cups water, 1 cup sugar


Stop. I think 2 cups water and 1 cup of sugar may give you a sugar concentration that is too high. 4 cups water is closer to what people usually use, so I'll take that as the baseline in the rest of the cases



> quote:
> 
> Change 1: double yeast
> Possible Effect 1?: the the CO2 production reaches the same steady state X of CO2 production 2x faster
> Possible Effect 2?: The CO2 production will ALWAYS be 2x faster and you will have to change the solution twice as fast.


Effect 1 is all that happens, and it is an easily observable effect. Effect 2 doesn't happen. The highest population density in a yeast culture is constant. Within reason, no matter what amount you start with the ultimate population is fixed at the same level. Since the population stays the same, the CO2 production rate stays the same. The limits are that if you put in way too much yeast you can get a fouled mixture. If you put in too little there may not be enough nutrients in the mix to support the usual maximum population density.



> quote:
> 
> Change 2: double the sugar
> Possible Effect1: none since the production is limited by the alcohol produced and not by the food available.
> ...


Not much change at all, in my experience. Effect 1 is true. The amount that is ultimately produced is limited by the alcohol content. Effect 3 is only partly true. It doesn't last much longer because the same yeast population produces alcohol at about the same rate and is limited at about the same time. If you were really to start with 2 cups of water, then doubling the sugar would probably make Effect 2 come true. Life would be impossible for the little yeasties. You would have syrup.



> quote:
> 
> Change 3: Double water
> Possible Effect1?: none
> Possible Effect2?: the rates will be the same, but the alcohol dilution means that the yeast will not be limited by poisoning and will allow to produce C02 for a bit longer


Same as halving the yeast and sugar. Slower startup. Effect two would be interesting to test. CO2 might be produced longer at a lower rate.



> quote:
> 
> Change 3: Double the sugar and water
> Possible Effect1?: same production rate, but have 2x the time before having to change


Like halving the yeast; you get slower startup. With a larger volume of solution the ultimate yeast population is larger and you double the production rate.



> quote:
> 
> Change 4: Double all
> Possible Effect1?: Production rates double, but all else remains the same.


That is right. If you want to double the production rate, then just double the volume of the mixture and double the yeast dose to keep the startup rate the same.

Roger Miller


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## Jon Mulzer (Mar 9, 2003)

You all mention alcohol content as being what ultimately kills the yeast. This may be possible but I once read a transcript of a conversation that an aquarist had with a long time home beer and wine maker. From the man's replys he seemed to know quite a lot about yeast and their lifecycles. He said that to reach an alcohol level that would be harmful or fatal to the yeast you would need a mix that would basically be syrup. What he said caused the yeast to stop fermenting was the pH of the solution they were in. He also suggested adding baking soda to help stabilize the pH of the solution to help get longer lasting mixes. I have done this since I started using DIY CO2 and my mixes routinely last longer than 2 weeks. I usually change them out at the 2 1/2-3 week mark. I wish I were able to find the article but I have been looking for 30 minutes now and I give up.









Hope this helps the discussion.

Disclaimer: Any errors in spelling, tact, or fact are transmission errors.


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## 2la (Feb 3, 2003)

> quote:
> 
> Originally posted by Roger Miller:
> Effect 1 is all that happens, and it is an easily observable effect. Effect 2 doesn't happen. The highest population density in a yeast culture is constant. Within reason, no matter what amount you start with the ultimate population is fixed at the same level. Since the population stays the same, the CO2 production rate stays the same. The limits are that if you put in way too much yeast you can get a fouled mixture. If you put in too little there may not be enough nutrients in the mix to support the usual maximum population density.


Hi Roger, can you elaborate on how the maximum yeast population is fixed for a given amount of water? If you doubled the amount of yeast to start with, what keeps the maximum number of activated cells from increasing? Also, I only made the "blind" comment tongue-in-cheek, as some aspects of this I have indeed tried.







I use to use a 2-cup sugar, 1-tsp yeast recipe that barely lasted 2 weeks. I eventually hit upon a recipe of 1 cup sugar, 1/4-tsp yeast that reproducibly lasted 6 weeks, but the confounder was that I also added a quarter-teaspoon of baking soda to the mix.

Jon, my understanding--and I'm sure I'll be corrected in a flash if I'm wrong--is that when alcohol levels reach roughly between 10% and 15% by weight, yeast begins to die. That said, I'm not sure how adding baking soda increases the life of the mixture (it does, by experience), but my guess is that it buffers the carbonic acid in solution produced by CO2 reacting with water?

 
(Click for pics)


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## Roger Miller (Jun 19, 2004)

> quote:
> 
> Hi Roger, can you elaborate on how the maximum yeast population is fixed for a given amount of water? If you doubled the amount of yeast to start with, what keeps the maximum number of activated cells from increasing?


My information came from two home brewers who posted some detailed discussions of yeast culture on APD several years ago. You can get the same information from any number of other sources The yeast population density in any environment is capped at a maximum value in cells/cc (called Carrying Capacity) that is independent of the initial population. I don't know what the actual mechanism is. Perhaps further reproduction is inhibited at that population density.

When you double the amount of yeast that you start with the population gets to the maximum density faster. With less yeast the culture will eventually get to the carrying capacity, it just takes a little longer. The nutrients that the yeast use to grow on come from dead yeast in the yeast culture. If you add very little culture then you might create a population cap that is lower than the maximum capacity. That would happen if the amount you added didn't contain enough nutrients to support the maximum population density.

Roger Miller

[This message was edited by Roger Miller on Wed June 04 2003 at 09:36 AM.]


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## anonapersona (Mar 11, 2004)

A few coments from my aborted experiments in DIY CO2...

The pH is indeed an important factor. But so is the type of yeast. It seems that bread yeast does better with baking soda, but brewing yeasts, that is ale yeast and champagne yeast do not. Most experiments with brewing yeasts and baking soda were duds (though I cannot rule out errors on my part with old yeast and leaks and so on)

CarpGuy did some research about brewing yeasts and said that wine makers add acid to the batch at the start, to keep bad bacteria from fouling the mix. So, brewing yeasts are not hurt by acidity. And brewing yeasts tolerate higher alcohol levels.

On the other hand, bread yeasts do much better with some baking soda. Baking yeasts, baking soda, there might be something to that. In current tests, a mix with 1 Tablespoon baking soda with 1/2 cup sugar and 1/4 teaspoon bread yeast with 2 cups water is making over twice the bubbles of the same mix with 1/2 tablespon baking soda, one week into the run. 

Now, about sugar. I found that adding extra sugar to the Hagen/Nutrafin prepackaged mixes significantly slowed the startup and the max rate. More sugar is not a good thing. Very strange to us Americans, but sugar is an inhibitor, like salt, used to preserve meats and fruits. While it is a fuel, it is also a preservative. Too much inhibits cellular activity.

As I said, I gave up on the experiments. After I got all the parts collected to run side-by-side trials, I got concerned about blowing a bunch of yeasty air into the house. bubble scrubbers seemed too much work. 

Now, I run the Hagen/Nutrafin bottles in the 10 and 20 gallon tanks on bread yeast and baking soda and the bigger 29 gallon tank on champagne yeast and gelatine with yeast nutrient. 

I'm still playing with the best mix for the 29 gallon, trying to get a smooth rate, not too high (since the canister filter does not blow off the excess CO2 like the HOB filter did) but long lasting, minimum fuss. 

Now I'm using 1/4 of the Knox Blocks gelatine batch with 1/4 teaspoon wine yeast and 1/4 teaspoon yeast nutrient in a 2 liter jug with lots of air space for the minor foaming. Lasts 2 to 3 weeks and I can dump 1/2 the water and add more gelatine and tap water to extend the run.


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## 2la (Feb 3, 2003)

Thanks, Roger--great info as usual. Any idea exactly how much yeast is 'enough' for a typical 2-liter reactor? For example, could we use an eighth of a teaspoon and get the same results? (Anything to make the dollar stretch farther...









 
(Click for pics)


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## Roger Miller (Jun 19, 2004)

2la,

I've used as little as 1/8 teaspoon. It was a long time ago, but I recall that it took more than 24 hours for the batch to get up to speed. If there was any difference in the production rate from the mature culture then it was too small to make a lasting impression on me.

I later went to larger amounts of yeast, but it was to get a quicker start-up, not to get a higher production rate.

Roger Miller


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