Why Does Brie Smell of Ammonia, and Can You Fix It?

Your brie smells of ammonia because it is ripening, and possibly because it has ripened too far. Breaking down protein is the whole point of a bloomy rind cheese, and ammonia is a by-product of that process. A faint whiff at the rind is normal. A sharp hit that stings the back of your nose means the cheese has gone past its best, or that it has been suffocating in cling film.

The good news is that the second cause is extremely common and usually fixable in half an hour. Here is how to tell which one you have.

Where the ammonia comes from

A brie is ripened from the outside in by Penicillium camemberti, the white mould on the rind, working alongside enzymes from the milk and the rennet.

Those enzymes chop the casein protein in the paste into smaller peptides and then into free amino acids. That is what turns a chalky white disc into something soft and spreadable. But amino acids do not stop there. As they break down further, they shed their nitrogen groups, and that nitrogen leaves as ammonia gas.

Two other things make it more noticeable:

• The mould consumes lactic acid at the surface, raising the pH as the cheese ripens. At higher pH the ammonia stays in its volatile gaseous form rather than dissolving into the cheese as ammonium, so you smell far more of it.
• Ammonia is a gas, and gases need somewhere to go. Wrapped tightly in plastic, a brie sits in its own exhaust.

So an ammonia smell is not contamination or a fault at the dairy. It is the cheese doing exactly what it was made to do, just further along than you wanted.

Is it safe to eat?

Ammoniated brie is unpleasant rather than dangerous. The quantities in a wedge of cheese are tiny, and the smell puts you off long before anything else would. Eat a slightly ammoniated slice and you get a bitter, faintly metallic mouthful. That is the extent of it.

What you should not eat is a brie showing real spoilage: a rind gone slimy and pink or grey rather than white, blue-green fuzz on the cut face, brown liquid pooling at the edges, or a sour, yeasty smell that is nothing like ammonia. Soft cheese does not tolerate uninvited mould, so bin the whole thing rather than cutting round it.

None of this is medical advice, and if you are pregnant or immunocompromised the guidance on soft mould-ripened cheese is different again, so speak to a health professional rather than an article about cheese.

The 30 minute fix

Most of the time the ammonia is trapped, not terminal. Try this before you write the cheese off.

1. Unwrap it completely and throw the plastic away.
2. Put it on a plate or a board at cool room temperature.
3. Cover it loosely with greaseproof paper or a clean tea towel. Not plastic, not an airtight lid. It needs to breathe.
4. Leave it 20 to 45 minutes, then smell it again.

Ammonia is volatile, so it simply blows off. If the smell fades and what is underneath is buttery and mushroomy, the wrapping was the problem all along. This works surprisingly often on supermarket brie, which spends its life sealed in film.

If it is still stinging after an hour, or tastes bitter and slightly bleachy, the cheese has gone too far. Ripening only runs one way.

How to tell an overripe brie by looking at it

Ripe and ready:

• The rind is white to pale cream, maybe with a few rust or beige mottles, and it feels dry and slightly velvety.
• Pressed gently in the middle, it gives like the fleshy pad below your thumb.
• Cut it and the paste bulges slowly. It does not flood the board.
• It smells of mushrooms, cream and warm stone.

Not ready yet:

• A firm, chalky white seam through the centre of the wedge with softer paste either side.
• Tastes of plain, slightly sour milk.
• This is fixable. Leave it somewhere cool for a few days and it will keep ripening.

Gone too far:

• The rind has browned, sunk, or shrivelled away from the paste, and feels tacky or slippery.
• The paste has collapsed entirely and runs like custard, often with a brownish tinge just under the rind.
• It smells of ammonia straight out of the wrapper, before you have cut it, and keeps doing so after airing.
• The taste is bitter or metallic rather than savoury.

How to buy brie at the right ripeness

• Buy a cut wedge from a counter where you can. You can see the paste, and a good cheesemonger will let you taste it and tell you honestly when it will peak.
• Watch the wrapper. If the paste is pushing out of the sides and sticking to the film, it is ripe now. Buy it for tonight, not for Saturday.
• Press the middle gently through the paper. Firm all the way through means underripe, yielding but springy means ready, and a soft spot that stays dented means past it.
• Look at the rind edge. White and slightly furry is good. Grey, sticky or collapsed is not.
• Ask when it will peak. This is the single most useful question in a cheese shop and almost nobody asks it.
• Buy small. A whole small wheel keeps far better than a cut wedge, because the rind protects everything underneath. If you are two people, buy a 250g wheel and finish it.
• Know what you are buying. Brie de Meaux and Brie de Melun are protected raw milk cheeses from France with real character and a real timetable. Most supermarket brie is a pasteurised, stabilised version built to sit on a shelf, and when it turns ammoniated it is usually because it was over-wrapped. Worth browsing the catalogue to see how many bloomy rind cheeses there are beyond the obvious two.

How to store brie so this does not happen

Get it out of the plastic. Cling film is the main villain in this story. It traps moisture and gas against the rind, the surface goes wet, and the ammonia has nowhere to escape.

Instead:

• Wrap in waxed or greaseproof paper, or proper two-layer cheese paper if you have it. The rind needs a little air exchange without drying out.
• Put the wrapped cheese in a loosely closed box or bag, not a vacuum-tight one.
• Store it in the warmest part of the fridge, which is usually the vegetable drawer, around 4 to 8C. Colder slows ripening but also makes the paste chalky and mutes the flavour.
• Rewrap in fresh paper each time you cut it. Reusing damp paper reintroduces the problem.
• Eat a cut wedge within three to five days. Brie is not a keeping cheese.
• Take it out of the fridge a full hour before serving. Cold brie tastes of very little, and half the complaints about supermarket brie are really complaints about temperature.

Quick answers

Does an ammonia smell mean brie has gone off? Not necessarily. It means the cheese is well ripened and the gas has been trapped. Unwrap it, air it for half an hour and smell it again. If it still stings, it is past it.

Can you cook with ammoniated brie? If it is mild, yes. Baking a whole wheel with honey and thyme covers a slight edge. If it is strongly ammoniated, heat concentrates the off notes rather than hiding them.

Why does the rind smell stronger than the paste? Because ripening happens at the rind. That is where the mould lives, where the enzymes are most active, and where the ammonia is produced.

Do other cheeses do this? Yes. Camembert, Chaource, Brillat-Savarin and any bloomy rind goat's cheese all go ammoniated when overripe, and washed rinds can too. The cause is identical.

How long does brie keep in the fridge? About a week unopened past a good purchase, and three to five days once cut. Check it by feel and smell rather than trusting the date.

A properly ripe brie is a completely different cheese to the cold, chalky one most people have had, and worth something unexpected alongside it. When you find one at its peak, note the maker in your cheese tracker so you can buy it again.