Rennetability

Rennetability is a measure of how readily milk coagulates in the presence of rennet, an enzyme or enzyme preparation used in cheese making. It describes the ease with which casein micelles form a curd under standardized conditions and is a key property for predicting cheese yield and texture.

Several factors influence rennetability. Biological and processing factors include species and individual variation in milk composition; pH of milk at the time of rennet addition; temperature during coagulation; calcium concentration and the overall mineral balance; fat content can affect gel formation; and prior heat treatment such as pasteurization or UHT can alter casein micelles and reduce rennetability. Milk storage conditions, age, and freshness also matter. The source and dose of rennet or coagulant and the presence of rennet inhibitors or adulterants can modify outcomes.

Measurement and interpretation: Rennet coagulation time (RCT) is a common measure, defined as the time from rennet addition to the onset of gel formation under standard conditions. Some laboratories use formal rheological tests to assess curd firmness over time. In practice, milks with short RCTs are described as having high rennetability and tend to produce fast-set curds with strong yields, whereas milks with long RCTs are said to have low rennetability and may require process adjustments.

Applications and implications: Rennetability informs cheese-makers when selecting milk for a given cheese type and may influence process control, acidification steps, and rennet dosing. It is considered alongside other milk quality factors, such as casein content and coagulation properties, to predict cheese texture and yield. There is no single standard definition, and tests may vary by method and dairy region.