Tuesday, 12 November 2013

A preservative worth its salt

Salting is one of the oldest methods of preserving food. It’s also convenient for the home cook as no specialist equipment is needed. Common salt is quite good enough to use as a preservative – the other commonly used is saltpetre (sodium nitrate plus potassium nitrate). 

Salting includes both dry salting, where the food is covered in salt, and brining, where the salt is dissolved in (most often) water and poured over the food. 

The way salting works as a preservative is by osmosis. You will remember osmosis from chemistry lessons at school – water will move through a semi-permeable membrane from a weak solution to a strong one. In their natural state, plants (ie, foodstuffs) contain salts and minerals in weak solution, in which bacteria live happily. The salt draws moisture from the foodstuff, drying it out slightly, and inhibiting the bacteria from reproducing.

Additonally, salting halts the action of enzymes which can contribute to the decay of foodstuffs. When you put sliced apple into brine or an acid solution like lemon juice to stop it from browning, this is using the brine or acid to stop enzyme activity. 

Foods that are commonly salted include fish: salt cod is practically national dish in some countries; cabbage, in the form of sauerkraut, and also the Korean dish kim chee; beef – Jewish salt beef, for example; and vegetables – think of the many tinned vegetables you buy that are preserved in salt.

Then there are the popular middle Eastern preserved lemons, which are simply salted lemons, and which you can easily make yourself. These are made best with small lemons which you can sometimes find in middle-Eastern stores; if not, you can use ‘normal’ sized lemons, or try preserving limes, or even satsumas instead, using the same method detailed here (updated from our post on citrus gifts, December 18th, 2012.

Preserved lemons 
6 lemons 
Sea salt 

Give five of the lemons a quick wash and dry. Slice each lemon into four wedges but don’t cut right through the lemon – leave the wedges attached at the stem end. Rub the sea salt into the wedges and pack into a wide-necked, preferably sterilised, 1-litre jar. 

Put the kettle on. 

Sprinkle a tablespoon of salt over the lemons in the jar, then juice the last lemon and add this to the jar. Top up with boiling water, then seal the jar. Leave for a month before using. 

Unopened, these keep really well in a cool dark place. After opening, keep in the fridge.




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