Calcium Chloride

The half-teaspoon that makes shop milk behave like farm milk. Pasteurisation shifts soluble calcium out of solution and a rennet gel needs it back — which is why a weak, mushy set from perfectly good milk is usually a calcium problem rather than a rennet one.

What it is

Calcium chloride is a salt, sold as a solution or as flakes, and in cheesemaking it does exactly one job: it restores the soluble calcium that heat treatment moved out of the milk.

Calcium is structural. The casein micelles that make up a curd are held together partly by calcium phosphate, and the gel that forms after renneting depends on enough calcium being available in solution. Pasteurisation shifts some of that calcium into an insoluble form, and the result at the vat is a set that is slow, weak and mushy — from milk that is otherwise perfectly good.

What it does and does not fix

It fixes: a weak or slow set from pasteurised shop milk. This is the common case and it is worth reaching for before you start doubting your rennet.

It does not fix ultra-pasteurised (UHT) milk. UHT denatures whey proteins so thoroughly that the milk cannot form a rennet gel at all, and calcium chloride will not change that. Check the carton — US organic milk is frequently UHT — because this is the single most common reason a first cheese fails.

And it is not a licence to over-use. Too much gives a curd that is tough and rubbery rather than clean-cutting, and it can carry a faint bitterness of its own.

Using it

The usual dose is around a quarter-teaspoon of 30% solution per gallon of milk, diluted in about a quarter-cup of unchlorinated water and stirred in before the rennet. Follow your recipe’s figure over this one; strengths differ.

The other place it matters, which people miss

Brine. A saturated brine that contains no calcium will pull calcium out of the cheese sitting in it, and the result is a wheel with soft, slimy, degraded edges. A brine wants roughly 0.25% calcium chloride and to be acidified to about pH 5.0 so it is in equilibrium with the cheese rather than stripping it.

That is not an optional refinement. It is the difference between brining a cheese and slowly dissolving its surface.

Substitutes (if absolutely necessary)

• Better milk — the real substitute. Low-temperature-pasteurised or (where legal and you trust the source) raw milk needs little or no calcium chloride, because nothing took the calcium out.
• More rennet — commonly suggested and mostly wrong. It gives a faster set, not a stronger gel, and the surplus enzyme keeps working through the aging and can turn the cheese bitter.
• Note: there is no kitchen-cupboard stand-in. This one is cheap, keeps for years, and is worth simply having.

Where to find it

• Online: cheesemaking suppliers sell it as a 30% solution in small bottles, which is the convenient form.
• Local store: brewing and home-canning suppliers carry it (it is also a pickle-crisping agent, sold for that purpose), and it appears in some hardware stores as a de-icer — buy the food-grade product, not that.
• Storage: the solution keeps almost indefinitely; flakes are hygroscopic and want a tightly closed jar.