Brewer's yeast CO2 generator

I made a CO2 generator out of a 2 liter bottle. I use brewer's yeast, water, and regular sugar. It is producing CO2, but I am wondering if I should have the bottle sealed. Right now I just leave the top off. I have an air lock that will let the CO2 out but no oxygen in. Should I use this? Or does it not matter since CO2 is heavier that O2 and the bottle will be filled with mostly CO2 all the time? I have also heard this will help with they yeast smell, and I can tell if CO2 is being made because the water in the air lock will bubble.

I guess my main question is does the yeast need fresh O2 in order to ferment the sugar?

One other thing. Should the bottle be light proof? Bread needs the dark. Is it the same for brewer's yeast? Or is the clear plastic bottle ok?

jebus2029 said:

I made a CO2 generator out of a 2 liter bottle. I use brewer's yeast, water, and regular sugar. It is producing CO2, but I am wondering if I should have the bottle sealed.

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No, you'll have a bomb on your hands if you seal up that 2 liter. Just leave the airlock on.

I guess my main question is does the yeast need fresh O2 in order to ferment the sugar?

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Yeast needs o2 in order to fully function, but dry yeast is made to have plenty of energy stored in the form of glycogen. Ideally if you were making beer, you'd aerate your wort before pitching your yeast, but that's not necessary given the size of your fermentation.

Your experiment is interesting but you wont get more than a few days worth of a minuscule amount of CO2 off of a two liter fermentation. Even with a larger, 5 gallon fermentation, I can promise you it would not be worth the time/money/energy to maintain such a thing and see any measurable results.

I've heard of plenty of other people doing this and saying it works great. A few cups of sugar will last a few weeks. You just have to shake it everyday. I noticed with the last one I made that had the air lock it would bubble right after I shook it and then slow down so maybe you are right. It is very inconsistent. I think there are buckets with a specific mixture you can order that work in the same fashion but continue to work nonstop for a few weeks. I can't remember what was inside to cause the CO2 to be created. They also recommended putting a plastic bag over the outlet during the dark period since they won't need it at night. Then in the morning open the inflated bag to fill your grow space.

poke pin holes in a balloon, put it over the tip of the bottle, itll let you know you still have c02 and it releases slowly, doesnt need to be dark

homebrewer said:

No, you'll have a bomb on your hands if you seal up that 2 liter. Just leave the airlock on.

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I agree.


I think you need to block the light from the grow lights from getting into the 2 liter

jebus2029 said:

I've heard of plenty of other people doing this and saying it works great. A few cups of sugar will last a few weeks. You just have to shake it everyday. I noticed with the last one I made that had the air lock it would bubble right after I shook it and then slow down so maybe you are right. It is very inconsistent. I think there are buckets with a specific mixture you can order that work in the same fashion but continue to work nonstop for a few weeks. I can't remember what was inside to cause the CO2 to be created. They also recommended putting a plastic bag over the outlet during the dark period since they won't need it at night. Then in the morning open the inflated bag to fill your grow space.

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I'm a homebrewer, I know what I'm talking about. This method will not work. A few cups of sugar will fully ferment in less than a week and produces most of the co2 in the first 4 days of fermenation. In the event that you didn't pitch enough yeast to fully attenuate your liquid, you'll get a slow ferment and eventually a stalled fermentation. Airlock activity well into the second week is just air working it's way out of the liquid and is not a sign of fermentation. Take my advice, you're better off dissolving the sugar and watering your plants with it than you are trying to ferment it to plump up your yield.

Can't really tell if it is working or not. Was worth the experiment though. If I ever find the thread that went into detail about how it is done I'll post a link here.

jebus2029 said:

Can't really tell if it is working or not. Was worth the experiment though. If I ever find the thread that went into detail about how it is done I'll post a link here.

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The byproducts of fermentation are alcohol and co2. If done on a larger scale (5 gallons), your experiment would work on a really small grow as the amount of co2 produced is not that great. It's just not worth the money and effort. For one week of constant fermentation, you'd need a liquid with a specific gravity of 1.065 which would take 7 lbs of cane sugar in 5 gallons of water. Between the brewers yeast and sugar, that's $10 per week and at the end of the week, you're stuck dumping out 5 gallons of prison wine.

But this hobby is all about experimentation and I salute your effort.

Mmmmmm, prison wine. Just like Grandpa use to make. Good times. Good times.

He did it in the bathtub. Said he liked a natural fermentation.

Very informative posts Homebrewer, nice one.

With all due respect to Homebrewer, the info in this article does seem to suggest that yeast based generation in a 2l bottle can be useful:

https://www.rollitup.org/do-yourself/162265-co2-via-yeast-right-way.html

In summary, 1 cup (a half-pound) of sugar can produce up to 1000 sq.ft. of enriched air for a grow room. Recipes typically utilize 2 cups in a 2l bottle-- giving 2000 sq. ft. over 4-7 days. Given air circulation etc, that is not a lot for a big room, but would be plenty for a small closet or cabinet grow. It is a technique I plan on using in my next harvest.

Nitegazer said:

With all due respect to Homebrewer, the info in this article does seem to suggest that yeast based generation in a 2l bottle can be useful:

https://www.rollitup.org/do-yourself/162265-co2-via-yeast-right-way.html

In summary, 1 cup (a half-pound) of sugar can produce up to 1000 sq.ft. of enriched air for a grow room. Recipes typically utilize 2 cups in a 2l bottle-- giving 2000 sq. ft. over 4-7 days. Given air circulation etc, that is not a lot for a big room, but would be plenty for a small closet or cabinet grow. It is a technique I plan on using in my next harvest.

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Just to correct your facts here; a pound of sugar will ferment into approximately half a pound of ethyl alcohol (C2H5OH) and half a pound of CO2. One pound of CO2 makes 8.7 cubic feet of CO2 gas at normal atmospheric conditions. Your half pound of sugar ferments into 2.175 cubic feet.

If someone REALLY feels like wasting their time, try this recipe that I posted in the worthless 'Homemade CO2 thread':


If you want a system that works, and mind you this will work for a small closet grow and that's all, you need to increase the batch size and change the ratio of sugar to water. Only one pack of yeast is necessary as when yeast go through the phases of respiration, fermentation and sedimentation, your cell count increases 4 fold. A Brewery will recycle yeast and for this amateur-hour project, you can too. Except you're not concerned about fusel alcohols, phenolics and ester production. That means you can use one pack of yeast for the rest of your life.

One Gallon of water
1.4 lbs of sugar
1 pack of Safale S05 dry ale yeast (only 2 grams are needed out of the 11 gram pack)

This 1.065 mixture should ferment for about 1 week giving you a constant flow of CO2. Ideally, you should really double the batch size (and the ingredients) to get any kind of decent CO2 production. Ferment this in a 3 gallon pale with the lid off even. You also need to make sure that you aerate the mixture at some point before fermentation has started as yeast need food (sugar in this case) and O2 to thrive. An airlock is not needed yet won't hurt as they are only useful when sanitation is a concern. At the end of the week, the yeast will have flocculated to the bottom of your container. Mix up a new mixture of sugar and water, dump out your fermented batch of prison wine, but make sure to leave at least half of the beige sludge in the container as that yeast will ferment your next round.

The concern I have is that is this really worth the 25 Lbs of sugar during flower that's needed to add any measurable amount of CO2? I'd say save the money and add an intake fan.

Looking back at this post, I'd probably recommend an even larger batch size of 2-5 gallons.

homebrewer said:

If someone REALLY feels like wasting their time, try this recipe that I posted in the worthless 'Homemade CO2 thread':

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Well, you write like someone who knows more about this subject than I do. Not sure I follow your logic, though. Why isn't C02 generation a viable option for small or cabinet grows? The numbers you use suggest that a 2l bottle could be enough for a 30 sq.ft. cabinet (my flowering space).

BTW, my estimate of 1000 sq.ft. was for the volume of "enriched air", not pure CO2.

Nitegazer said:

Well, you write like someone who knows more about this subject than I do. Not sure I follow your logic, though. Why isn't C02 generation a viable option for small or cabinet grows? The numbers you use suggest that a 2l bottle could be enough for a 30 sq.ft. cabinet (my flowering space).

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Don't get me wrong, sugar, water and yeast in the right proportions will always produce CO2 and alcohol. I'm just questioning it's worth in terms of cost, maintenance, and end result on your crop. A small closet grower would do well to do a side-by-side comparison with clones to see if a fermentation can assist the crop. But is a small closet grower experienced enough to keep all variables in-check except for the addition of CO2? Are the results repeatable by the same grower time after time?

I also have to worry a lot more about air leakage...

Your points are well taken homebrewer, I will give it a shot for my grow at some point, but I will grow another crop for a baseline comparison.

I assume this type of small system isn't large enough to be toxic to humans?
i'm using a rubbermaid box. And something on this scale would be a great way to test if it works.
I could try this after my current grow. I think however any little bit helps, as long as cost overweights it

Just buy a tank and be done with it. If this only works on small grows like closets and cabs, you're not going to have enough room anyway.

Don't listen to anybody who has not done this. I am a home brewer as well. I am telling you it will work. The balloon idea with the holes in it is the best. Baecuse you will get a steady flow of co2. When u first do it fill the container half way with water. And in 2 to 3 weeks u add more sugar and shake it up and in 2 to 3 weeks repeat untill it is full or gushing liquid out. Best to keep it on a towel. You don't have to keep it in the dark. Because your not making beer or wine, you don't care about the flavor. U will attract nats and fruit flies. Clean the outside of your bottle with ammonnia to get rid of them. Pray peroxide water in your grow room around the bottle and your plants to help keep them at bay. You can spray your plants with diluted ammonnia too. Good fertilizer