There are a number of co2 supplementation devices on the market that use yeast and sugar to produce co2 for your grow box. They have mixed reviews and are typically overpriced for what looks like a painted soda bottle. The real question is: how much CO2 do they produce and is it economical?

The chemical equation above represents the beautiful reaction responsible for producing alcohol. My friends over at uWaterloo did an experiment calculating how much CO2 is produced via fermentation of 20g of sugar.

Now they used a high amount of yeast to sugar and at a high temp so their fermentation was complete in 6 hours. By adjusting the temperature and amount of yeast you can stretch this out to 1-2 weeks. The yeast was microwaved to 110F in the experiment to really speed things up. My beers actively ferment over 3-10 days depending on how much yeast I pitch and the temp.

Walmart here in Ontario, Canada sells sugar for ~ $1/kg. Given the results above you should expect 1kg to produce 0.400 Kg of Co2 or just under 1 lb. It costs me $30-40 to fill up a big 20lb tank of co2 at my local hydro store. If I use sugar to produce co2 it costs me only $20 for 20lbs! Going into this article I was not expecting this, most forums threads I found had people saying it would be horribly uneconomical.

This means you can get into co2 supplementation without having to invest in a pricey co2 regulator and tank. You do lose the ability to have the ppm fine-tuned but in my experience, on a small scale, it is not necessary. You are not going to produce enough co2 to kill your plants from a few carboys of fermenting beer and I have not noticed any ill effects from ppm above 2000.

So it turns out fermenting sugar is economical. But if you are going to go through all the trouble of fermenting, the doc thinks you may aswell brew some wine or alcohol while you’re at it!

I typically brew 2x 5 gallon batches of 1.050 beer (~4.5% ABV) producing roughly 4 lbs of co2 (and 10 gallons of a delicious session IPA). The cost of the co2 goes up almost ten-fold but you are now getting delicious beer too.

If you are going the sugar route I recommend using turbo yeast. Turbo can tolerate ABV exceeding 17% while most beer yeast will struggle past 10%. No matter which setup you use, be sure to run an airlock to prevent the co2 from introducing unwanted products into your grow space. I keep the fermenters outside of the grow box and use airline tubing to pipe co2 in.

In practice, I have found that my ppm fluctuates between 800 and 1800 during active fermentation. My baseline CO2 is around 400 ppm.

I bought the autopilot co2 monitor to measure the CO2 ppm in my grow box. I wasn’t sure if it would be worth the money at first but have found it to be very accurate. It gives you 1 day, 1 week and 1-month trends for CO2, temperature, and humidity. If you can afford it I’d recommend picking one up.

Here is a part-list for DIY CO2 supplementation showing how easy it is to get started:

• 2x 5 Gallon Carboy
• Sugar and Turbo yeast
• or Beer Brew Kit
• Airlock
• Airline tubing
• CO2 Monitor (Optional)

If going the sugar route I would start with 60% water to 40% sugar, adjusting as needed. Ferment at 70F. Start with a small amount of turbo yeast, you can always add more if needed. If fermentation is too fast it can be slowed down by cooling the carboy. What you want is rapid but not erupting bubbles in the airlock.

The buds closest to the airlock are always the densest and grow towards the CO2 source as if to get more. It’s awesome to see.

Here is a pic of the microbrewery next to my micro grow. I use large totes with a temp controller and 100W fish tank heater to keep fermentation temps at the 68F that California Ale yeast thrives at.