Acidification

Setting the milk. Fine cheese starts with clean fresh milk, preferably from the most recent milking. The milk is soured; its lactose (milk sugar) converted to lactic acid by bacteria. Acidification will occur naturally if milk is left to sour on its own by inherent bacteria, but cheese makers normally add starter cultures to jump start the process.

Traditional recipes involve creating a starter by using a small amount of the naturally soured milk from the day before, the way yogurt is made. This can be difficult and time consuming for a larger operations. Today many cheese makers add bacteria by way of commercially prepared starter cultures in the form of freeze dried powders or frozen liquid concentrates. These offer greater predictability, consistency and control.

After completing acidification, starter bacteria die and release their enzymes, which contribute to the breakdown of proteins and fats, a key step in successful cheese ripening and flavor formation.

As bacteria convert lactose into lactic acid, temperature and time measurements are critical. Bacteria multiply very rapidly, lactic acid bacteria may continue their fermentation for a long time during cheese making, both during and after coagulation. The rate of acidification is the most important measure of a starter culture because it determines the curds (and cheeses) eventual pH (acidity) as well as their moisture and mineral contents.