Is mouldy cheese safe? When cutting it off works

A green spot on the corner of a block of cheese. Everybody has the same reflex: cut the mouldy bit off, eat the rest. For some cheeses that reflex is correct. For others it is a bad idea. What separates them is how hard the cheese is.

The short answer

Cheese	When you see mould
Hard cheese (cheddar, parmesan, aged varieties)	Cut off at least 2.5 cm (1 inch) around and below the spot
Semi-hard, sliced	Same rule — but discard thin slices entirely
Soft cheese (feta, cottage, cream cheese, ricotta)	Throw it all out
Grated or crumbled cheese	Throw it all out
Blue cheeses (roquefort, gorgonzola)	Their own veining is normal; discard if a foreign colour appears

The distinction comes from the USDA's guidance on mould, and it rests on a single mechanism.

Why hardness is the deciding factor

The green-blue patch you can see is only the visible part of the mould. Mould sends out root-like threads, and those threads are the real issue: some species produce mycotoxins, poisonous compounds concentrated in and around them.

A hard cheese's dense structure stops those threads from travelling far, which is why cutting with a generous margin works. In a soft, moist cheese the threads can spread throughout — the part that looks perfectly clean may not be. Grated cheese cannot be rescued for the same reason: enormous surface area, and every piece touching every other.

When you do cut, keep the knife from touching the mould; slicing the clean part with the same blade re-contaminates what you just saved.

Roquefort is mouldy — so is mould harmless?

No. The mould in blue cheese is a deliberately chosen culture grown under controlled conditions (usually Penicillium roqueforti). Mould that appears by itself in your fridge is an unknown species.

The practical rule: the blue veining belongs there; if something of a different colour shows up — pink, brown, fuzzy white — that is no longer the cheese's own mould, and the cheese goes.

How long does cheese keep in the fridge?

Unopened cheese is fine until the date on the packaging. Once opened:

Type	Fridge (after opening)
Hard cheese	3–4 weeks
Brined white cheese (feta)	1–2 weeks; longer if kept in its brine
Cottage cheese, ricotta, labneh	5–10 days
Cream cheese	~2 weeks

These are typical figures; the date on the pack and how you stored it come first. We covered how opening changes the date in how long do opened products last.

Practical ways to delay mould

• Let the cheese breathe. Cheese wrapped tightly in cling film suffocates in its own moisture and moulds sooner. Waxed paper inside a loosely closed box is a better combination.
• Keep brined cheese in its brine. The brine slows both drying and mould; if it runs low, top it up with salted water that has been boiled and cooled.
• A clean knife every time. Crumbs on the board and spores from the previous cheese are the quietest cause of mould.
• Not the coldest shelf. Near-freezing shelves dry cheese out and make it crumble; just above the crisper is better.

When in doubt

Three signs mean the rescuing stage has passed: a fuzzy, raised layer of mould, an ammonia smell, or a bitter taste.

For the general decision framework on food past its date, see is food safe after the expiry date.

To check how long a specific food keeps in the fridge, pantry or freezer, use our shelf life lookup.

Remembering which day you opened that cheese is the hard part. freshIt tracks your items automatically from your grocery receipt and reminds you as the date approaches — see how on the features page.