Acidification

Acidification is the process by which starter cultures of lactic acid bacteria (LAB) — most commonly Lactococcus lactis, Lactobacillus, Leuconostoc, and Streptococcus thermophilus — ferment lactose into lactic acid, progressively reducing the pH of milk from its natural 6.6–6.8 down toward the isoelectric point of casein at roughly pH 4.6. This pH drop has cascading effects on the milk system: calcium phosphate dissociates from the casein micelle matrix, weakening its structure and rendering the caseins more susceptible to rennet action; at the isoelectric point, the net charge on casein molecules reaches zero and they aggregate spontaneously without rennet at all (the principle behind quark, fromage blanc, and yogurt). In rennet-coagulated cheeses, acidification runs in parallel with enzymatic coagulation, and the cheesemaker must time and control both. Faster acidification produces more open, moist curds; slower acidification allows the rennet gel to set firmer before the mineral matrix weakens. The rate and trajectory of acidification — measured by titratable acidity or by pH meter at specified time points — is the most critical variable the cheesemaker tracks throughout a make; it governs moisture content, final pH, buffering capacity, and the entire downstream flavor chemistry of proteolysis and lipolysis during ripening. Direct acidification (adding vinegar or citric acid directly to milk) can achieve the same pH but bypasses the metabolic contributions of live cultures — aromatic diacetyl, CO2 for eye formation, bacteriocin protection — and yields cheeses with simpler flavor profiles.

“The cheesemaker tracked acidification hourly, expecting pH to fall from 6.6 to 6.2 by the time the curd was cut and reaching 5.3 by the end of the press.”

• ConceptRennet & Coagulation
• TechniqueCheddaring
• IngredientStarter Culture

1. 1.Technology of Cheesemaking — Barry Law & Adnan Tamime (2nd ed., 2010, Wiley-Blackwell)
2. 2.Cheese and Fermented Milk Foods — Frank Kosikowski & Vikram Mistry (3rd ed., 1997)
3. 3.Dairy Microbiology Handbook — Richard Robinson, ed. (3rd ed., 2002, Wiley)
4. 4.Mastering Artisan Cheesemaking — Gianaclis Caldwell (2012, Chelsea Green)

Confidence: high