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I got a bit confused when looking up nutrition values for milk versus kefir made from that milk. For some reason many tables list higher values of some nutrients (e.g. potassium and magnesium) than is in the source form, i.e. the milk.

Can someone shed light on how this would happen?

I realize that lactose from the milk gets turned into carbon dioxide and alcohol, but where does it take the additional nutrients from if the only nutrition for the kefir grains is the milk and air?

user110084
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0xC0000022L
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    Are the serving sizes the same? – Aaronut Jul 06 '11 at 01:45
  • Can you edit the question to provide links to an example of this? I've not seen it when looking up kefir stuff. – BobMcGee Jul 06 '11 at 04:42
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    I have never had homemade kefir. Does it produce a whey like yogurt does? Maybe it is measured after the CO2 evaporating somewhat and the whey thrown out. – rumtscho Jul 06 '11 at 07:35
  • @Aaronut: yes, they are. Mostly calorie tables are given per 100 ml or 100 g. – 0xC0000022L Jul 06 '11 at 13:32
  • @rumtscho: yes, it produces a little bit of whey. But I personally don't throw it away. The CO2 should mostly affect the lactose content, not other ingredients such as potassium or magnesium ... but I may be missing something. – 0xC0000022L Jul 06 '11 at 13:35
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    My point was that if they take 100g milk and make kefir out of it, and the CO2 evaporates and they throw out the whey, they are left with less than 100g kefir. Which means that the Mg and K are more concentrated. This would explain small differences, but not big ones. There is no USDA nutrition entry on kefir, but the difference in milk vs buttermilk is 10 vs 11 mg Mg, 132 vs 151 mg K, which is plausible as a concentration issue. And then, the real values vary from cow to cow, season to season, etc. With a low number of data points (USDA has 12 for buttermilk), a difference is expected. – rumtscho Jul 06 '11 at 14:10
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    @rumtscho is correct. 100g of kefir takes more than 100g of milk to make. It is the same reason why protein and Ca is typically much higher in cheese than in milk. The is mass loss from CO2 alone. Whey may or may not be separable depending on the age of the kefir. A one day old kefir at 20C will likely not have any. If you are only taking out the kefir "grains" for nutrition analysis, then the mass loss has to be well over 50%. – user110084 Jun 08 '17 at 18:21
  • @user110084: that last sentence doesn't make sense to me. Also, the CO2 is mostly created from digesting the lactose, right? So it should be at most the mass-equivalent to the lactose, usually less though (because it would be converted to lactic acid and CO2, right?)? Btw, I always stir any whey that may have separated right back in. Of course the *concentration* of the other components may change because of this transformation. – 0xC0000022L Jun 09 '17 at 06:03
  • Kefir often forms little clumps called "grains" within the body of thickened liquid. Many would drain off just the liquid for consumption and save the grains as starters. I have not actually taken measurements, but certain that grains and liquid have different composition and water content. You are stirring everything in, so the mass loss is exactly as you described. – user110084 Jun 09 '17 at 06:14
  • Well the grains are what you have to put into the kefir to get it started, so yeah I am removing those to start the next batch. But those grains are growing fairly slowly. Still, I'll concede that they would have to have an effect on the overall composition. I thought, though, that the discussion was about the whey versus the "curd" (well, perhaps not thick enough to warrant that term, but you get what I mean). – 0xC0000022L Jun 09 '17 at 06:47

2 Answers2

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It could just be the difference in milk sources. Different cows, receiving variable types of feed, produce milk with varying nutritional content. They probably only tested kefir using milk from one or at most two sources. In comparison, the figures for normal milk could be drawn from hundreds of dairy farms across the nation.

I would expect there to be changes in the carb/protein/fat content of the milk, as well as vitamins produced/consumed by the kefir. Specifically, the carbohydrate level should be lower from lactose being digested into lactic acid.

BobMcGee
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  • Agreed. The USDA lists ~60 data points for milk and 12 for buttermilk. So I doubt that the milk data is all that good too. But the kefir is probably even worse. Add to that that the stuff makes up only 1/10 000 to 1/1000 of milk, and you see how the measurement can be imprecise. I bet that for any nutrient, "has x g of carbohydrates" is as false as saying that my body temperature right now is exact 37.00 °C. – rumtscho Jul 06 '11 at 16:57
  • @rumtscho: yeah, I just got mainly confused by the fact that some nutrients seem to be only in either or that the amount should differ that much. Bob's answer is actually quite logical, though. Would perhaps make more sense to see in relation what milk and resulting kefir contain. I bet that would be more interesting. The milk I buy lists at least some of its ingredients ... so I would expect some changes but not really drastic ones :) – 0xC0000022L Jul 06 '11 at 17:18
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There are many products that the nutritional value changes with aging and kefir is one such. You are growing good bacteria and yeast while fermenting and this adds to the milk's value. Also if you do a secondary fermentation you increase some of those values (like the B vit.) ck

Calvin King
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  • Not so. You cannot create new mass and new elements that were not the system to begin with. In some cases, you have to include gases from the atmosphere, but this is definitely not the case with milk to kefir, you lose mass as @rumtscho commented – user110084 Jun 08 '17 at 18:16