Can you cut mold off cheese and eat the rest?

The short version, and it is genuinely a two-part answer: on a hard or firm cheese — cheddar, parmesan, gruyère, a block of Swiss — cut off at least a couple of centimetres around and below the spot, and the rest is fine to eat. On a soft, moist, shredded or crumbled cheese — ricotta, cream cheese, brie, feta, anything sliced or grated — the mould spot means the whole piece goes in the bin, not just the visible part. This is not an arbitrary rule of thumb. It follows directly from the same thing that decides how long any cheese keeps in the first place: how much water is in it.

Why hard cheese gets to keep the rest of the block

Mould does not just sit on the surface. What you see is the visible fruiting body; underneath it, thread-like filaments called hyphae reach down into the food looking for moisture, and they can travel further than the fuzzy spot suggests. In a dense, low-moisture cheese like an aged cheddar or a wedge of parmesan, that spread is slow and limited — the cheese simply does not offer the hyphae much water to follow, so the contamination stays close to where you can see it. Cut away a generous margin, wipe the knife rather than dragging it back through the mould, and the cheese underneath was never in the mould's reach to begin with.

This is exactly the same density-and-moisture logic that makes a block of aged cheese last for weeks once opened while a tub of ricotta is on borrowed time within days. A hard cheese is inhospitable to spoilage generally, mould included, for the same structural reason.

Why soft cheese does not get the same deal

A high-moisture cheese is the opposite environment: plenty of water for hyphae to follow much further than the visible spot, and a soft or crumbly structure with no dense barrier to slow them down. By the time you can see mould on a piece of brie or a tub of cottage cheese, invisible spread has very likely gone well beyond what a knife could trim away.

There is a second reason, and it is the more serious one. Soft, moisture-rich cheeses are already in the more cautious "use by" category of food generally, for the same reason pre-cut salads and fresh dairy are — the kind of bacteria that can travel alongside mould in a wet environment does not reliably announce itself with a smell or a visible change the way spoiled milk does. Trimming visible mould off a hard cheese removes what was actually there. Trimming it off a soft one only removes what you could see.

The cheeses that are supposed to have mould

Blue cheese, brie and camembert are mouldy on purpose — the blue veining and the white bloomy rind are specific, food-grade strains introduced deliberately during production, and they are safe to eat as part of the cheese, not a defect to work around. That is a different situation from contamination, and it is worth telling the two apart. If a different colour or texture of mould shows up somewhere it is not supposed to be — a fuzzy grey-green patch on a wheel of brie, say, distinct from its usual white rind — treat it like contamination on any other soft cheese: the whole piece, not just the spot.

How to actually do the cutting

• Go wider than feels necessary. At least a couple of centimetres around and below the visible spot, not just a thin skim off the top — the invisible edge of the contamination is further out than it looks.
• Do not drag the knife back through it. Cut in from clean cheese toward the spot and lift it away, rather than pushing the blade through the mould and then across the piece you plan to keep.
• Rewrap the cut face in something fresh. The offcut carried whatever spores were on the surface nearby; a clean wrap on the newly cut surface is a fresh start, not a formality.

What actually slows down the next spot appearing

Mould needs the same thing everywhere: standing moisture. A cut face sealed tightly under cling film traps condensation against the cheese, which is exactly what feeds the next spot fastest. Wax paper or dedicated cheese paper, which lets a cheese breathe slightly while still limiting how much air reaches it, keeps a cut block drier at the surface for longer than an airtight wrap does — a detail that matters more than which drawer it sits in.

None of this needs a mental catalogue of every cheese in the shop. It needs the one question that decides most of what happens to cheese in a fridge: how much water is in this. Dry and dense can be rescued with a knife. Wet and soft cannot, and the deliberately mouldy ones are their own, separate category once you know to look for the right colour in the right place. Munch's opened-item tracking is built around exactly this kind of thing — a per-batch date from the day you opened it, visible to everyone in the household, so the wedge at the back of the drawer is a known quantity rather than a guess made with a knife in hand.