Acid-set cheese

Acid-set cheese is milk that gelled because pH fell. FAO: adding acid lowers ionization on casein micelles; near a neutral charge (they give an isoelectric pH of 4.2) and with reduced hydration, a coagulum forms. The reaction depends on temperature: at higher temperatures the coagulum forms at a higher pH (less acid) ¹. That gel is typically soft and breaks easily — cottage and some fresh cheeses live here. Rennet is the other tool; cheddar identity uses both culture and a clotting enzyme ².

Yogurt is an acid gel you usually do not cut for whey. Acid-set cheese is the same idea taken toward drainage. Acidity is the shared chemistry.

Lemon or vinegar is still acid coagulation #

FAO’s fallback when you have no starter: pasteurize milk at 63 °C for 30 minutes, cool to 20–30 °C, add lemon juice, vinegar, or citric acid until the milk curdles, then drain in cloth about 6 hours in a cool place ¹. Those figures are their small-scale teaching, not a U.S. safety regulation and not a composition standard. Heat-acid precipitation of whey proteins is a different set — Ricotta.

What to notice #

The mass looks like yogurt, then weeps. It does not give a clean, rubbery break. Taste bright lactic or citrus, depending on whether cultures or lemon did the work. Over-acid, grainy, chalky paste is a pH and temperature problem. Under-acid, the gel never forms and you have sour milk.

Moisture stays high unless you drain and press. FAO’s fresh-cheese water range is 70–80% ¹. CDR: if you intend to age anything, verify moisture, fat, pH, and salt — a wet acid-set paste is not a cheddar ³. See Cream cheese and Coagulation.