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How much calcium in 24 hour yogurt? I use a half gallon of Organic whole milk & starter. I have heard yogurt has more calcium than milk after fermentation, but can find no measurements (or %DV)for calcium on homemade 24 hour yogurt.

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Calcium is an element, so the biological-chemical processes of fermentation can neither create nor destroy it (and it does not become a gas which could float away). Therefore, the calcium content of your end product will be exactly the calcium content of your ingredients, so you if you know how much calcium is in your milk and starter then you have your answer.

Note that:

  • This is true of the absolute quantity of calcium, not the proportional quantity (to take an exaggerated example, if 1 litre of ingredients produced 0.75 litres of yoghurt then even if the quantity of calcium was the same the proportion would be much higher).
  • It may be that the calcium after fermentation is in a different form which the body is more or less able to use (this is called bioavailability); you would need to research that question separately (my instinct, though, is that this is not the case).
  • As rumtscho's comment points out, if your recipe involves discarding whey or some other part of the mixture then this reasoning no longer applies, and you would have to investigate whether the whey/discard contains proportionately more or less calcium than the remainder of the ingredients. However, the recipes I have seen for 24-hour yoghurt don't involve discarding whey or any other part of the mixture.
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    I am not completely with you on the first note. If 1 litre of ingredients produces 0.75 l of yogurt, this means the OP threw away 0.25 l whey (unless you are implying that 0.25 l evaporated during the scalding? That would be really unusual). I wouldn't make any guesses about whether the calcium is all in the yogurt, all in the whey, or distributed in some unknown proportion between the two.
    – rumtscho
    Jan 10 at 21:23
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    @rumtscho I think the answer is close to right. The main calcium compound in milk (dicalcium phosptae) isn't very soluble in water (0.02g CaHPO4 per 100ml H2O) and binds to casein which will keep it in the yoghurt. However it's more soluble at low pH so the figure at my first (wikipedia link will be a slight underestimate of the solubility)
    – Chris H
    Jan 10 at 21:55
  • ... but it would take more research than I'm prepared to put in now to be absolutely sure. Approaching it from the other end we could consider the calcium in commercial yoghurts, but of course then we don't know how much whey is lost
    – Chris H
    Jan 10 at 21:57
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    @rumtcho I was just hedging against the possibility that the process involves some step with a change of volume (by evaporation, gas given off in fermentation, growth of culture or whatever) – the numbers were deliberately exaggerated to make the point about proportion. The recipes I saw when googling '24 hour yogurt' didn't involve discarding whey.
    – dbmag9
    Jan 10 at 22:20
  • I had a quick look at recipes, and some of the comments under them do imply discarding; others suggest whisking the final product so it may be that a little whey separates but not enough to worry about. My own yoghurt making is a more typical 8 hours
    – Chris H
    Jan 11 at 11:31

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