Rinds & Moulds

A rind is not packaging. On a great many cheeses it is a living community doing the ripening, and the difference between a bloomy brie, a stinking Époisses and a Roquefort is largely a question of which organisms you invited onto the outside and what you did to encourage them.

This page is who they are, what they do, and — the question everybody actually has — which fuzzy things mean throw it out.

The four you deliberately invite

Penicillium candidum — the bloomy rind

The white velvet on brie, Camembert and the triple-crèmes. A mould, sprayed on or added to the milk, which grows a dense white coat over a few weeks.

It works inwards: its enzymes break the paste down from the rind toward the centre, which is why a young one is chalky in the middle and a ripe one is spoonable, and why these cheeses are made small and flat.

Its failure mode is ammonia. P. candidum deaminates amino acids and releases ammonia, and past a certain point the cheese smells sharply of it and tastes acrid. A faint ammoniac note in a very ripe bloomy is normal; a strong one means it’s gone too far — usually too warm, too wet, or not enough air exchange.

Brevibacterium linens — the washed rind

The orange-red bacterium behind Époisses, Taleggio, Limburger, Munster and the Trappist cheeses. It is responsible for the colour and for the smell, which is frankly feet — B. linens is closely related to organisms that live on human skin, which is not a coincidence and is the reason the association is so strong.

You encourage it by washing the wheel — brine, sometimes beer or wine or spirits — repeatedly over weeks. The washing does two things: it keeps the surface moist and salty, which B. linens likes and most competitors don’t, and it physically discourages other moulds from establishing.

It is a smear, not a fluff. A washed rind should be tacky and orange, not furry.

Penicillium roqueforti — blue

The one that goes inside. Added to the milk or the curd, it then sits dormant, because it needs oxygen and a well-knit cheese hasn’t got any.

Which is why blue cheese is made the way it is: the curd is deliberately left open and loose rather than knitted tight, and the wheel is needled — pierced with channels — some weeks in. Air reaches the interior, the mould wakes up, and it grows along those channels. That’s why the veining follows lines rather than being random.

It’s the one family where a leaky, badly-knit curd is the goal, and I still find that satisfying.

Geotrichum candidum — the one nobody mentions

A yeast-like organism used as a rind conditioner, often alongside P. candidum. It deacidifies the surface — consuming lactic acid and raising the surface pH — which prepares the ground for the other organisms, since both P. candidum and B. linens prefer a less acidic surface than a freshly made cheese offers.

It also gives the slightly wrinkled, brainy surface texture on some goat cheeses. Overdone, it produces a coat that traps too much moisture underneath — “toad skin.”

Natural rinds, wax and bandage

Not every cheese wants a living rind.

A natural rind forms by itself: the surface dries and hardens, and whatever is in the air colonises it. Brushed regularly to keep the growth in check, this gives the mottled grey-brown rind of a traditional alpine or farmhouse wheel. It costs moisture — the wheel shrinks — but it breathes.

Wax seals the wheel completely. No breathing, no rind organisms, no moisture loss. It’s the simplest and most forgiving option for a home cheesemaker, which is why my own kit includes wax and a brush, and it’s how a lot of gouda-style cheese is aged. The trade-off is that you have removed a whole category of flavour development — and that any mould that gets sealed under the wax will keep growing where you can’t see it. The wheel must be clean and dry before waxing.

Bandaging — wrapping in cloth greased with lard or butter — is the traditional cheddar finish. It lets moisture out slowly and lets a dry natural rind form beneath the cloth, and it produces flavours a sealed block never will. Almost all commodity cheddar is now block-aged in film instead, which is cheaper and faster and is a genuinely different cheese.

🔴 Which fuzz means throw it out

The honest answer has a shape rather than a simple list.

Generally fine, on a hard cheese:

White, blue-green or grey powdery moulds on a hard, low-moisture wheel. Wipe with a cloth dipped in brine or vinegar, or cut it away with a generous margin — at least an inch around and below. A dense, dry cheese is a hostile environment and moulds have difficulty penetrating far.
White surface crystals, which are almost certainly calcium lactate and not mould at all.
Anything you deliberately introduced, obviously, behaving as it’s supposed to.

Throw it out:

Black mould. Not worth any argument.
Pink, orange or red slime that you did not cultivate — as distinct from a deliberate B. linens smear, which you will know about because you made it.
Fuzzy mould on a soft, high-moisture cheese. This is the important distinction: in a soft cheese the mould’s threads run right through the paste, so cutting off the visible part removes only the visible part. Discard the whole thing.
Anything smelling of ammonia beyond a faint note, or of solvent, or genuinely rotten as opposed to pungent.
Anything on a vacuum-packed or waxed cheese that has clearly grown inside the seal.

And the sensible rule underneath all of it: the more moisture, the less benefit of the doubt. A two-year-old hard wheel can be rescued. A young bloomy that has gone wrong cannot, and isn’t worth the risk given what can grow in soft cheese.

Cave hygiene, which is the real answer

Most rind problems aren’t really rind problems — they’re cave problems:

Still air grows mould on every surface. You want a gentle breeze.
Standing water and wet surfaces are the recurring villain.
Shelves are part of the ecosystem and eventually the wrong part. Take them out and clean them several times a year.
Space between and behind the wheels, or the faces that never dry will tell you about it.

Cross-contamination is worth a thought too: P. roqueforti is vigorous, and blue spores in a cave will find their way onto things that were not meant to be blue. If you’re aging blue alongside anything else, expect to have opinions about it eventually.

Next: melting — why cheddar strings, feta doesn’t, and halloumi just sits there and browns.