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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?

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Are the serving sizes the same? –  Aaronut Jul 6 '11 at 1:45
    
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 6 '11 at 4:42
    
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 6 '11 at 7:35
    
@Aaronut: yes, they are. Mostly calorie tables are given per 100 ml or 100 g. –  0xC0000022L Jul 6 '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 6 '11 at 13:35
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2 Answers

up vote 4 down vote accepted

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.

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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 6 '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 6 '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

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Thanks. Any authoritative sources on this? –  0xC0000022L Oct 23 '11 at 18:31
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