Recipes

    Cultures & Rennet: Buying, Storing, Dosing

    The science pages cover what these organisms and enzymes do. This page is the practical half: where I get them, how to keep them alive, and how not to dose them wrong.

    Where I buy

    New England Cheesemaking Supply Company, for most of thirty years. Their catalogue is deep, their site is a reference in its own right, and — as I only worked out while writing this section — it’s run by Ricki Carroll, who wrote the first cheese book I’d tell anybody to buy.

    There are other good suppliers: The CheeseMaker (Steve Shapson) and Glengarry Cheesemaking (Margaret Morris) among them — and notice that all three are run by people who also wrote books, which is a pattern worth knowing about when a recipe names a specific product.

    Storing cultures: the freezer, and keep water out

    Freeze-dried cultures are more robust than people expect, if you respect one thing.

    The numbers:

    • Shelf-stable roughly 12 months kept below 20 °C / 68 °F.
    • In the freezer, a sealed foil packet lasts about 1.5–2 years, and properly stored DVI cultures are often good beyond two years.
    • Keep them in the coldest part of the freezer, at a constant temperature — cycling is worse than cold.

    And the thing that actually kills them: moisture. Once you’ve opened a packet, water is the enemy, not warmth. So:

    • Fold the packet over and seal it, then wrap in cling film or foil.
    • Put it in an airtight container in the freezer.
    • Don’t let a cold packet sit open in a warm kitchen — condensation forms on it, which is exactly what you’re trying to avoid.

    A part-used packet treated that way will keep going for a long time. A part-used packet left in a drawer, or opened repeatedly in humid air, will quietly weaken and you’ll blame your technique.

    An expired culture is usually not dead, just slower. If a culture is past date and you use it, the likely symptom is sluggish acidification rather than nothing — which is survivable if you’re watching pH rather than the clock, and misleading if you aren’t.

    Dosing cultures

    DVI — direct vat inoculation — is the sprinkle-it-in packet. Doses are tiny and measured, and the packet tells you how much per gallon.

    A prepared mother culture is dosed completely differently: 1–2% of the milk by volume. As a rule of thumb, one small culture packet ≈ 2–3 oz of prepared culture — so a recipe written for one form needs converting for the other, and the conversion is not intuitive.

    Getting this backwards in either direction is a real error. Sprinkle-quantities of mother culture do nothing; 1–2% by volume of DVI powder would be absurd.

    ⚠ And check the culture matches the cook temperature before anything else. Mesophilic in a hot-cooked recipe dies partway through, acidification stops, and the recipe will not warn you. This ruins more wheels than dosing errors do.

    Rennet: strength, storage, handling

    The full comparison of animal, FPC, microbial and plant rennet is on the rennet page. Practically:

    Strength is the number that matters. Rennet is sold at different strengths and the unit is IMCU. “A quarter teaspoon” is meaningless without knowing which. Check the bottle against the recipe, and if the recipe doesn’t state a strength, work from the bottle’s own dose per gallon rather than the recipe’s volume.

    Liquid rennet lives in the fridge and loses potency over months — it’s the ingredient most likely to be quietly past it in a home kitchen. Tablets and powder keep longer, and the freezer extends both.

    Dilute in cool, unchlorinated water immediately before use. Two reasons, both real: chlorine deactivates it, and undiluted rennet hitting one part of the vat sets that part and not the rest.

    Then stop stirring once it’s distributed — the aggregation phase is building a network and agitation tears it as it forms.

    Too much rennet has a recognisable signature: a fast, brittle set that shatters instead of cutting cleanly, aggressive whey expulsion, and — because the surplus enzyme stays in the curd and keeps working — bitterness months later.

    The other bottles

    Calcium chloride, if you’re using shop milk. Pasteurisation shifts soluble calcium out of solution and weakens the rennet set; CaCl₂ puts much of it back. A real correction, not an optional extra — and don’t overdo it, because excess makes the curd tough and can be tasted.

    Also the ingredient that stops a brine pulling calcium out of your cheese, which is a separate and under-appreciated job.

    Lipase, for the sharp piquancy of provolone and some Italian cheeses. Works fast, very easy to overdo, and excess reads as soapy or rancid and cannot be undone. Measure it.

    Annatto, if you want the orange colour of a Double Gloucester or an American cheddar. Purely cosmetic, and worth knowing that’s all it is.

    Adjunct cultures — P. candidum, B. linens, P. roqueforti, Geotrichum, propionibacteria — are sold separately from your starter and are not included in a generic “Swiss-style” or “brie-style” blend unless it says so. ⚠ This is a real trap: my own Swiss came out with no eyes, and one candidate cause is simply not having P. freudenreichii in the vat at all.

    What I’d keep on hand

    The short list that covers most of what a home cheesemaker makes:

    • A mesophilic starter and a thermophilic starter
    • Rennet — chymosin, animal or FPC, for anything you intend to age
    • Calcium chloride
    • Non-iodised salt
    • And then adjuncts per project, since they’re the ones that expire unused

    Everything except the salt lives in the freezer or the fridge, and the freezer means a couple of years rather than a couple of months.

    Next: mother cultures and brines — the two things worth making yourself rather than buying.

    Sources

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