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Yogurt is known to have lactose consuming bacteria (lactic acid bacteria/LAB), which consume lactose, break it down to glucose and galactose and produce lactic acid from the glucose and release the galactose. Evidently, this reaction cannot completely finish off all the lactose because lactic acid builds up in the yogurt, reducing the rate of LAB consuming lactose further and producing more lactic acid. Thus, the pH becomes the limiting factor, in a way. What if we artificially controlled the pH and let the LAB keep consuming more and more lactose? One way would be to add baking soda or other ingredients to raise the pH, but it seems that with higher pH, spoilage might become a concern - after all, low pH values are known to impede spoilage-causing bacteria/mold. Nevertheless, couldn't it be possible to add just enough baking soda to raise the pH to a level where LAB can keep consuming lactose but not enough to let mold/spoilage causing bacteria to grow? If such a pH range exists, it should be possible to keep the yogurt in that pH range using baking soda and a pH meter to judge how much baking soda is needed.

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  • The resultant yogurt would be pretty salty thanks to all the sodium lactate....
    – Sneftel
    Dec 6, 2023 at 11:04
  • @Sneftel I did some calculations using molar weights, and assuming that there are 16 grams of unfermented lactose in 500 grams of yogurt, converting all those 16 grams of lactose to sodium lactate would require about 16/342 * 23 grams of sodium from sodium bicarbonate, which is about one gram of sodium. That's the equivalent of adding less than 3 grams of salt to 500 grams of yogurt. Depending on one's palate, it might be classed as slightly to moderately salty. Dec 6, 2023 at 13:36
  • But you could use, e.g. calcium carbonate and not add any saltiness...though from what I recall simply going to a longer fermentation time than commercial production basically gets you there, without additives.
    – Ecnerwal
    Dec 6, 2023 at 17:23
  • @Ecnerwal See this: journalofdairyscience.org/article/S0022-0302(82)82198-X/pdf Even after 11 days of storage, the lactose content of yogurt only decreased from 4.8 g/100 g to 2.3 g/100 g - a modest decrease, but this is not anywhere close to completion or whatever would be considered "lactose free" in commercial market dairy products. As I mentioned in the question, the more the lactic acid that gets produced, the lower the pH gets, and the less the bacterial lactase enzyme works. Dec 8, 2023 at 11:56
  • It won't be simply "salty", salts other than NaCl frequently give food an unpleasant off-flavor, and if you have just a bit of too much baking powder left free, you'll also have a bad soda taste. And then there's curdling. All in all, this seems like a particularly unattractive project: it would require lots of effort, it would be difficult to get it to work, and if it works, even the beset outcome is likely to be pretty bad. And it duplicates a commercial product that's easy to obtain (at least for many people in our audience).
    – rumtscho
    Dec 8, 2023 at 12:25

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