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Instead, they said warehouses containing the mineral fertiliser saltpetre had exploded - a claim ridiculed by Ukrainian officials.

To keep it from melting, the ice was treated with potassium nitrate, otherwise known as saltpetre.

It’s all about nitrates and nitrites, which have traditionally been used to keep meat pink and kill botulism: saltpetre, which you use in the salt beef, is potassium nitrate.

As Jane Grigson explains in Charcuterie and French Pork Cookery, saltpetre was traditionally used when brining hams to give them “an attractive rosy appearance when otherwise it would be a murky greyish brown”.

The struggle has its origin in the exploitation of nitrates, used for fertiliser and to make saltpetre for the manufacture of gunpowder, in the Bolivian littoral, whose sparse population was mainly Chilean.