What happens to the calories?

[strantor]

I'm looking for an answer on a layman's level. I'm having trouble working out in my mind the relationship between calories before and after fermentation. My initial thought was that they are the same, because the volume of the fluid remains the same, and because calories are a measure of energy, which cannot be created or destroyed.

But I think that's wrong, because fermentation does give off low grade heat over a long period, which probably totals a large expenditure of energy. Plus a gas is given off, which must mean that some of the mass is displaced as well as energy. So the final alcoholic product MUST have less calories than the original sugary fluid, correct?

So is there some way to determine how many calories are in the original solution, how many are burned in fermentation process, and how many exist in the final product?

 

[b-boy]

I think you'd need a lab analysis to do a proper job of determining that. There are too many variables that can change, and each batch is going to be a little different.

 

[BigEd]

I'm looking for an answer on a layman's level. I'm having trouble working out in my mind the relationship between calories before and after fermentation. My initial thought was that they are the same, because the volume of the fluid remains the same, and because calories are a measure of energy, which cannot be created or destroyed.

But I think that's wrong, because fermentation does give off low grade heat over a long period, which probably totals a large expenditure of energy. Plus a gas is given off, which must mean that some of the mass is displaced as well as energy. So the final alcoholic product MUST have less calories than the original sugary fluid, correct?

So is there some way to determine how many calories are in the original solution, how many are burned in fermentation process, and how many exist in the final product?

Some of the recipe programs will give you a calorie count. Yes the calories are less in the beer than in the original ingredients because you are leaving various proteins and some carbohydrates behind. I'm no nutritional expert but my understanding is that the calorie count of a food or beverage is dependent on what the human body can digest and utilize. BTW the heat of fermentation is from the metabolic processes of the yeast, not unlike your body heat provided by your digestive system burning its fuel.

 

[ajdelange]

You can use ASBC MOA Beer-33 to get an estimate and it's pretty simple:

kCal_per_100 grams = 6.8*abw + 4*(TE - Ash)

1 kCal = 4.184 kjoule
TE is the true extract of the beer and Ash is the percentage ash. Ash is usually very small so you can ignore it or use a typical value like 0.1 or 0.2

A local brew pub's wee heavy measured 6.74% abw and had a true extract of 9.35 °P. From this we estimate that the OG was 21.7 °P. Assuming that ash was .2% the caloric content of the wort would be:

kCal/100g = 6.8*0 + 4*(21.7 - 0.2) = 86 kCal

At the completion of fermentation:

kCal/100g = 6.8*6.74 + 4*(9.35 - 0.2) = 82.4

From this it is apparent that most of the energy is transferred from 6 carbon sugars carbohydrate bonds to 2 carbon alcohol carbohydrate bonds with the rest used by the yeast and emitted as heat.

If this is more than just curiosity I will leave it to you to determine how to estimate or measure true extract from final gravity and how to get abw from abv.

 

[forstmeister]

Beersmith estimates calories per 12 oz serving. I assume its based on a reasonable model since the other calculations in there are pretty accurate.

 

[callemann]

As far as I remember: The calories in the finished fermented is definately lower. The yeast cells are using the carbohydrates in "glycolysis" breaking them down first to pyruvate, then lactate which also happens when humans eat carbohydrates(depending to a certain degree of oxygen availibily). There are plenty of energy(calories) extracted in this process as ATP(and NADH->ATP). There yeast cells on the other hand can also break down lactate(when starved of oxygen) to alcohol extracting even more calories and releasing some of the carbon skeleton as CO2. Humans on the other hand can not to this, and lactate accumulates in tissues under oxygen deprivation(It can however be converted back to glucose in the liver). Point is alcohol is partially metabolized sugar during anaerobic conditions in yeast cells, and therefore contains less energy than the original carbohydrate. Sorry for the rant

 

[ajdelange]

When humans produce lactate they are actually fermenting. Under normal conditions they respire. The amount of energy extracted by respiration is much greater than the amount extracted by fermentation. As you can see from the numbers in #4 the amount of energy in the alcohol is almost as much as the energy in the wort. It would be the same for lactate in an animal. We only ferment when oxygen isn't available.

 

[millsware]

I thought this was an interesting question so I did some quick calculations. You are right in saying that the heat given off from fermentation indicates calorie reduction.

To keep it simple, assume all fermentable sugars are glucose. Non fermentables won't change.

180 grams of glucose (1 mole if you remember chemistry) gives 92 grams of ethanol.
glucose = 4 cal/g, ethanol = 7 cal/g
180 grams of glucose = 720 calories, 92 grams of ethanol = 644 calories.
This is about a 10-11% drop in caloric value from the fermentable sugars.

 

[ajdelange]

As far as I remember.. The yeast cells are using the carbohydrates in "glycolysis" breaking them down first to pyruvate, then lactate which also happens when humans eat carbohydrates(depending to a certain degree of oxygen availibily).

In yeast cells pyruvate is decarboxylated (that's where the CO2 in fermentation comes from) to acetaldehyde and the acetaldehyde reduced by NADH to ethanol. In a resipring animal pyruvate is passes to the tricarboxylic acid cycle and then feeds into the oxidative phosphorylation chain where CO2, water and ATP are produced. This pathway produces lots more ATP than fermentation which is why the bond energies of the original sugar are so much more efficiently used in respiration. In fermentation most of that energy goes into the waste product, EtOH. In respiration most of that energy goes into ATP (i.e. is stored for use by the body).

 

[Banana_Delivery]

You can use ASBC MOA Beer-33 to get an estimate and it's pretty simple:

kCal_per_100 grams = 6.8*abw + 4*(TE - Ash)

1 kCal = 4.184 kjoule
TE is the true extract of the beer and Ash is the percentage ash. Ash is usually very small so you can ignore it or use a typical value like 0.1 or 0.2

A local brew pub's wee heavy measured 6.74% abw and had a true extract of 9.35 °P. From this we estimate that the OG was 21.7 °P. Assuming that ash was .2% the caloric content of the wort would be:

kCal/100g = 6.8*0 + 4*(21.7 - 0.2) = 86 kCal

At the completion of fermentation:

kCal/100g = 6.8*6.74 + 4*(9.35 - 0.2) = 82.4

From this it is apparent that most of the energy is transferred from 6 carbon sugars carbohydrate bonds to 2 carbon alcohol carbohydrate bonds with the rest used by the yeast and emitted as heat.

If this is more than just curiosity I will leave it to you to determine how to estimate or measure true extract from final gravity and how to get abw from abv.

Such a beautiful answer to this exact question that I just googled