Skip to content
Bixa ProductsBixa Products
Rennet 101

What Does Rennet Do in Cheesemaking?

Short answer

In cheesemaking, rennet coagulates the milk so that a cuttable curd forms. It also influences how firm that curd becomes, how cleanly it cuts, and — in cheeses that are held or aged — how the protein breaks down during ripening.

By Bixa Products, Editorial teamUpdated January 20, 20265 min read

Three jobs, not one

  • Coagulation: converting fluid milk into a gel that can be cut.
  • Curd behaviour: contributing to how the curd firms up and how cleanly it releases whey when cut.
  • Ripening: in cheeses that are aged, residual coagulant activity participates in protein breakdown over time.

That third job is why dosage matters more in aged cheese than many people expect, and why excessive coagulant is associated with bitterness in some ripened styles.

Why the same rennet behaves differently in different milk

Two batches with identical dosage can set at different speeds. Protein and calcium content vary by season, breed, feed and stage of lactation. Heat treatment changes protein availability. pH at the moment of addition changes enzyme activity.

Coagulation is never controlled by one variable. Milk composition, temperature, pH, calcium, the cheese style and your process conditions all shape how the curd forms — the coagulant is one input among several.

About the author

Bixa Products — Editorial team

Educational content written by the Bixa Products team, a family-owned cheesemaking ingredient company specializing in rennet and chymosin. Technical guidance is written conservatively: where a value depends on your milk, process or product, we say so instead of guessing for you.

  • Family-owned cheesemaking ingredient company
  • 30+ years in the Latin American cheesemaking market
  • Specialists in rennet, chymosin and milk coagulation

Keep reading

All articles
Rennet 101

What Is Rennet and How Does It Work?

Rennet is a milk-coagulating ingredient used in cheesemaking. It contains enzymes that act on the milk protein casein so that liquid milk forms a curd firm enough to cut, drain and turn into cheese.

7 min read
Cheesemaking Science

How Milk Composition Changes Coagulation

Milk composition changes how milk coagulates. Protein and calcium content have the largest effect on set time and curd firmness, and both vary with breed, season, feed, stage of lactation and animal health.

6 min read
Cheesemaking Science

What Determines Curd Firmness?

Curd firmness is determined by milk protein and calcium content, temperature, pH, coagulant dosage and how long the gel is left to develop before cutting. No single one of these controls it on its own.

5 min read