Casein is typically produced from skim milk (rarely from buttermilk), and it can be done in one of three ways:
(1) naturally soured casein curdles when enough lactic acid develops from the milk sugar being fermented by
the ever-present bacterium Streptococcus lactisi; (2) acid casein is precipitated by adding dilute hydrochloric
acid or sulfuric acid; or (3) for rennet casein, warm skim milk is set with rennet extract until the In each of the
three techniques, the curd is washed with water, pressed or drained, dried in warm air, ground, and packaged for
sale. The calcium phosphate from the milk is largely preserved by rennet casein.