CO2 from Fermentation (Sugar and Yeast)

by Mark
(North Carolina)

I have read that adding yeast and sugar will produce CO2. If so, would using a 5 gal bucket with a small air pump in it create a constant flow of CO2? I really respect your knowledge of all things hydroponic, and want to thank you for all your invaluable info. THANKS AGAIN!!

Answer: Mark- I used to have a home wine making website also, so this is a subject I know doubly well. Many wine recipes call for 5 pounds of sugar, in water, in a 5 gallon primary fermenter. As yeast consume sugar, they produce both alcohol and CO2 as waste. Unfortunately, there are several problems with trying to use this kind of CO2 for your indoor garden.

First, the CO2 system will require almost as much maintenance as your nutrient reservoir to keep everything moving smoothly. Second, the amount of CO2 produced by a 5 gallon bucket full of sugar water and yeast is not nearly as much as the amount of CO2 you actually need to bring a small 4' x 4' garden up to the ideal CO2 level (apx. 1200 to 1500 ppm). In fact, I would estimate it is about 1/5th of what you would actually need....and once you begin ventilating the grow room area to control the high temperature, your CO2 requirements go up from there.

Finally, the buckets will use up the sugar (and stop producing CO2) in about 8 to 14 days. This means you will have to empty and refill each 5 gallon bucket at least twice over the course of your flowering period. By the time you set up and maintain multiple 5 gallon buckets to meet your CO2 requirements, you will have spent around $75.00 in sugar alone (assuming sugar is $3.00 per 5 lb bag).

Now compare this to tank CO2- I have found refills online for a 20 pound tank ranging from $12.00 to $20.00. Personally, I would recommend a 35 pound tank....there is less refilling and it is large enough to handle a 4' x 8' garden without having to refill. Also, a 35 pound tank is much easier to handle and move around than a 50 pound tank when full. The cost of the tank, the pressure regulator, and the release valve/timer are all one-time expenses, just like buying 5 gallon buckets (with lids) to use as primary fermenters would be a one-time expense.

However, even at $45.00 for a 35 lb tank refill, you begin to recover your extra initial expense (compared to the sugar method) starting with the very first crop. Check around town in welding shops, fire extinguisher rechargers, and gas supply stores for the best price on a refill. For detailed information on getting your CO2 levels right, make sure to read my Plant Growth and CO2 page.

If you decide to try the fermentation method, you will need to sterilize the sugar water with Campden tablets 24 hours before you add the yeast. This kills any bacteria in the solution. This is important because bacteria will consume any alcohol present and will leave behind vinegar. It is likely to also produce a horrible smell and to stop your CO2 production. For this reason, you will want to use a tight fitting lid on each 5 gallon bucket. For the same reason, you will NOT want to place an air bubbler into the fermenter....as CO2 is produced by the yeast, gas pressure will build up and naturally push the CO2 gas out through an airlock in the top of each lid (p.s.- you will need airlocks).

Just one final piece of advice- I only recommend adding CO2 to a garden if your garden is already problem free and producing good results. If there are problems in your garden, or any of the growth influencing factors are not in their ideal range, than adding CO2 will not fix the problem and it is likely that you will not notice the benefits of adding the CO2. Hope this helps you out Mark, and Happy Growing!