I have been fermenting vegetables, kimchi for the most part, for a few years and am familiar with the general arc of the process, as well as observing how active my ferment is.

Yesterday, I started a half gallon of sauerkraut, a half gallon of white kimchi, and a couple pints of fermented beets. Today, I am working up nutritional values for each in support of a Keto eating plan. I've had no trouble working up the raw calories, fat, net carbs and protein for each recipe. Yet I know that fermenting will change the carbohydrates and perhaps other values.

I am aware there is no one-size-fits-all for this calculation, rather the opposite, it seems the number of variables is too broad to pin down any kind of equation. Case in point, I have three ferments going, all burning at a different pace. That said, I'm looking for any kind of rough approximation based on experience.

Two facts seem certain. One, that the fermented product will have a lower carbohydrate value than the cumulative raw ingredients. And two, the resulting carbohydrates will never reach zero. That leaves the rate of burn. Based on your experience, what would you expect the carbohydrate burn to be in a highly active ferment for something like Napa Cabbage, Red Cabbage, or Beets?

Less important, but of keen interest, should I expect the other values (cals, fat, or protein) to change as the result of fermentation?

  • 1
    Hi, and welcome to SA! Have a look at the tour and help center when you get a chance. Just so you're aware, questions on health effects of food are generally off-topic. That is not to say your question (which I think is interesting) is, though.
    – LSchoon
    Jul 9, 2020 at 7:29
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    I agree this is on-topic as it is about chemical changes to food as part of a cooking process and not about benefits.
    – GdD
    Jul 9, 2020 at 8:30
  • @LSchoon you may want to look at the nutrient composition tag. I know this is weird, because it is an exemption from an exemption :) but we basically allow questions on how a named nutrient changes during cooking. The separation line is: If the question requires the answers to make judgements on what is healthy (e.g. the question is "which good things disappear during fermentation" and by answering "X disappears", the answerer has implicitly declared X to be a healthy substance) it is off topic. If the OP has set a measurable goal for their food composition, and the reason for that was...
    – rumtscho
    Jul 9, 2020 at 9:42
  • ... their personal health belief, we take the question - because we don't have to tell them what is healthy, just how to achieve a certain objective state of their food which they happen to believe is healthy. We do prune discussion on whether the belief is founded or not, though, and just focus on the literal question.
    – rumtscho
    Jul 9, 2020 at 9:43
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    @BuffaloRabor Answering your own question is encouraged! An answer should be an answer, though: if it is a follow-up question, you should ask that as a separate question. If it is an 'update' to the current question, you can always edit your question.
    – LSchoon
    Jul 9, 2020 at 20:02

1 Answer 1


on the "Less important, but of keen interest" question:

let's talk carbs instead of cals here. cals are potential chemical energy stored in carbohydrates, fats, proteins, etc. in vegetable fermentation, the fat and protein content is not a significant contributor to potential calories, so i'll confine this to carbohydrates

microbial fermenters' (effective, not comprehensive or quantitative) ...

most who do this don't track a carb burn rate, but they definitely notice when the jars quit bubbling. CO2 output rate is directly proportional to carb burn rate, but those are very difficult to measure without specialized equipment

there are two ways that fermenting usually stops, when fermenters

  • run out of food (mostly carbs)
  • byproducts (here, lactic acid) are concentrated enough to halt reproduction

so if the jar's quit bubbling, it's important to understand that it might not be down to near zero carbs

inputs are

  • carbs
  • minuscule amounts of protein and trace minerals

outputs are

  • more fermenters
  • carbon dioxide, which is not retained by most canners
  • lactic acid
  • compounds that lend funk to flavor and aroma

note that fermenters consist mostly of: water, lipids (structural and energy storage), and protein (structural and information storage)

to answer the keen interest ...

  • net change in carbs? yes. down
  • net change in protein? yes. up, but not by much
  • net change in fat/lipids? yes. up, but not by much
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    @pleasepassthechese is it safe to say calories are consumed "in proportion" to the consumption of net carbohydrates during fermentation? Jul 10, 2020 at 17:00
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    yes, it's safe to say that Jul 11, 2020 at 18:42

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