Why is ash used in cheese-making?

Ever wondered about the pale grey dusting of ash on the outside of a goats cheese?  Or the thin wavy layer of black ash round running through the heart of Morbier, Humboldt Fog and Ashcombe cheeses?  Why is it there? What does it do?  Where is it from?….

Well, up until the 1990s in France the ash used in cheeses literally was wood ash taken from the fire grate. But today things are different, and the ash on the outside and inside of cheeses is fully edible.

What is the ash used in cheese?

Since the early 2000s cheese-makers have bought in ‘food grade ash’ or ‘vegetable ash/charcoal’, the proper technical name of which is ‘activated charcoal’.

‘Activated charcoal’ is made by heating a ‘combustible natural product’ to a very high temperature without oxygen (so it does not burn), then grinding it into a powder. Common ‘combustible natural products’ include coconut husks, bamboo, grapevines and any food safe, non-poisonous wood such as sycamore, hazel, maple, ash and beech. Dense wood tends to be the best, apparently. But even vegetables would work if they were dry enough to burn.

Activated charcoal is different from regular charcoal because it goes through a further step in production – usually by passing steam through it – which removes the impurities and makes it more porous with a greater internal surface area.

As well as its use in foodstuffs (where it is used to add colour to things like charcoal biscuits, breads, ice creams, and cocktails) it also appears in water filters, air filters and for medical use (where the porous nature can be useful to help absorb toxins and chemicals), as well as toothpaste and skincare products. It doesn’t create a gritty texture in food, and it is technically tasteless, odourless, and sterile. It even passes through the human body undigested!

So why use ash in cheese?
It has three main benefits:

  1. Appearance. It creates a great contrast in a cheese – especially a pale white goats’ cheese – either on the rind, or as a vein running through the middle; like in Morbier. On the outside of the cheese it will often change colour from jet black to a blue-grey colour as the cheese ages and the rind forms. It also can cover up any potential defects on the rind – black mould (mucor) and blue/green spots often appear on some natural-rinded goats’ cheeses. People often don’t like the look of the mould or spots, especially on a white- or cream-coloured cheese, even though they are perfectly edible. The ashing of the rind means that when the imperfections grow they are much less noticeable, so everyone happily eats them and comes to no harm! It’s an old-fashioned marketing trick still in use today ;-).
  2. To keep flies off. In the olden days applying ash was also helpful in drying the rind, making it much less attractive to flies looking to lay eggs. Nowadays, however, better pest control such as fly zappers, sealed rooms, fly screens on windows, etc. means this is not so necessary.
  3. To help the rind form. The ash not only helps dry the rind, it also de-acidifies (neutralizes) the rind. This means the white moulds and wrinkly yeasts commonly associated with goats’ and Brie-style cheeses find it easier to grow. Goats’ cheeses, in particular, are often quite acidic in their make, so adding ash to the rind helps provide a favourable environment for their rind community of moulds and yeasts to start to grow, that will in turn help the cheese mature and develop more complex, ‘tertiary’ flavours.

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