How much CO2 does the fermentation produce?

In the last article, link here, we analyzed the heat generated by the fermentation and their distribution in the fermentation curve. Today we will focus our attention on CO2 produced during fermentation. I hope you enjoy the reading! Please, subscribe to this article to read a new article every week!

The easiest way to start this article is to talk about the classic Gay-Lussac formula, where 1 mol of glucose (or fructose) is converted to 2 mols of ethanol and 2 mols of CO2.

As the molar mass of glucose is 180,16 and CO2 is 44,01, following this formula we may say the CO2 generated by fermentation is equal to sugar x (44,01 x 2) / 180,16, or simple sugar times 0.48857.

Carl Joseph Napoleon Balling also studied the relationship between sugar and alcohol (and CO2). He considered in his equation that a small part of the energy is used to produce yeast matter (he called ‘losses’).

Following Balling reasoning, while producing 1 g of ethanol, yeasts also produce 0.9565 g of CO2 with 0.11 g of losses and a consumption of 2.0665 g of sugar. With that in mind, we may say that CO2 production is mass of sugar x 0.9565 / 2.0665 (or sugar x 0.46286).

We cannot forget that not all sugar consumed in fermentation follows the ethanol pathway. A part is used to produce glycerol and trehalose or even ends up as organic acids. The precise quantity depends on several factors, such as yeast strains, fermentation conditions, and stress applied.

We may say that around 90 – 95 % of the sugar will be converted into ethanol + CO2. I like to consider 93 % as a number to feed the equation. This ratio must be multiplied by the Balling equation we mention before. The complete equation became like this:

Where the m is mass (volume of wort x density), the OE is the original extract, and the RE residual extract (both in Plato, decimal).

Let’s consider the same example of the last article, a 10.000 l of 1.048 wort, starting with 12 °P and finishing with 3°P of residual sugar.

Doing the math, we can conclude this fermentation will produce 406,01 kg of CO2. As it happens with the heat, the CO2 generation is not homogeneous, an ‘average calculation’ would be a lie. The production rate will always depend on sugar consumption. Applying this equation to a curve of fermentation, we can see the ratio in every step of the fermentation.

Analyzing the graph, we had zero surprises on realizing that the max CO2 production is on the hochkr?usen, achieving a peak ratio of 18.05 kg/h of CO2. Just to comparison, the average is 5.35 kg/h. We must not consider the average on the piping or equipment definition; otherwise, we would mess up badly.

Thank you for reading! If you enjoyed it, please like and share it, and comment on your opinions about the topic and suggestions for the next articles!