After coagulated milk is cut, moisture is lost. This has tremendous effects on the final cheese.
Syneresis refers to the expulsion of whey (i.e. moisture) after the coagulated milk has been cut. As milk coagulates, casein micelles are assembling into a 3-D matrix that makes up final cheese texture. As the casein network forms and contracts, it squeezes out the trapped whey. If cheese is a sponge, then syneresis is squeezing the water out of that sponge. The amount and extent of syneresis has an effect on the final moisture content (obviously), and by extension the texture and flavor.
There are a few ways syneresis can be accelerated:
- Cutting curd into smaller pieces (like with Grana-style cheeses) – more surface area allows for more whey to leak out
- Cooking the curd – heating the curd can contract the protein structure squeezing out whey
- Stirring the curds/whey – the motion and agitation can encourage whey expulsion
- Pressing the curds – literally squeezing the sponge
- Salting the curds – salt draws out moisture
- Acidification – starter is producing acid which can encourage syneresis