Culturing

What a culture actually does

Updated October 2026

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The acid sets the gel And the acid is the preservation Temperature decides which organisms work Time is not the measurement Cultures age Keep the culture somewhere separate References

A culture is doing one chemical job with two consequences. It converts lactose to lactic acid, and that acid both sets the texture and defends the product.

The acid sets the gel

Milk protein is held in suspension at the pH of fresh milk. As acid accumulates, the proteins lose that stability and form a network, which is the set you are after. Texture is therefore a function of how far the fermentation went, not something you add.

And the acid is the preservation

A cultured product is more hostile to spoilage than the milk it came from, which is why cultured dairy keeps longer than fresh. That is the same mechanism the pickles property runs on, arriving in a product nobody thinks of as preserved.

Temperature decides which organisms work

Different cultures have different optimum temperatures, and holding the wrong one gives a slow, incomplete or off-tasting fermentation. The incubation temperature is therefore a specification with a number rather than a warm place, and it is the most common thing to get casually wrong.

Time is not the measurement

Fermentation speed varies with the milk, the culture’s condition and the temperature, so the same number of hours gives different results on different days. The finishing point is a pH, which is where the next page goes.

Cultures age

A culture propagated from batch to batch drifts in composition as the organisms in it compete, which shows up as a slow change in flavor and set over months. A commercial culture bought to a specification does not. Neither is wrong and they are different businesses, and the first one needs a plan for renewal.

Keep the culture somewhere separate

A working culture stored next to production is a culture that will eventually be contaminated by whatever else is being made. Keeping the stock culture physically apart, and renewing from it rather than from yesterday’s batch, is the cheap insurance against losing the thing your product is built on.

References

21 CFR 131.200, Yogurt: not less than 3.25 percent milkfat and not less than 8.25 percent milk solids not fat, with “a pH of 4.6 or lower measured on the finished product within 24 hours after filling.” law.cornell.edu

21 CFR 114, Acidified Foods, whose 114.3 definition turns on a finished equilibrium pH of 4.6 or below, the same figure the yogurt standard uses. law.cornell.edu

Written from federal regulation and FDA guidance, not from a laboratory. Pasteurization of milk and milk products in final package form for interstate commerce is a federal requirement, and what your state permits inside its own borders is a separate question. Anything here is a starting point for a conversation with your state department of agriculture, not a determination that you comply.