Rennet, Explained: Animal, Vegetable, Tablets & Strength

What rennet is, which type your cheese wants, and the tablet trap.

Rennet is the enzyme (chymosin) that sets milk into curd. Cultures make acid; rennet makes the gel. You usually need both.

The four types

• Animal (calf) rennet — typically about 90% chymosin. Retailer guidance: the best choice for longer-aged cheese, because its residual components help protein breakdown finish properly.
• Vegetable / microbial rennet — from the mold Mucor miehei (no mold is in the final product). The vegetarian default. One warning from the retailer FAQ: it can impart a slight bitterness in cheeses aged past about 6 months.
• Fermentation-produced chymosin (FPC) — pure chymosin made by fermentation (e.g. CHY-MAX). Works for any cheese type; often sold double-strength, so dose at half.
• Thistle (cardoon) rennet — the traditional plant coagulant for certain Iberian sheep cheeses. Style-specific; flavours and soft-paste effects are a specialist topic.

Forms and handling

Liquid is easiest to measure precisely; tablets and powder store longer and travel better in warm climates. Rennet works from about 85–105°F and is not deactivated until roughly 140°F. Always dilute it in cool, non-chlorinated water and add it promptly. And cut on time — rennet keeps firming the curd past the recipe point.

The tablet trap

There is no universal 'tablet'. One brand's half-tablet sets 2 gallons; another brand's full tablet sets 1 gallon. Dose tablets by your own packet, never by a chart. Junket rennet is a weaker dessert product — it is not cheesemaking-strength rennet.