Ice Filtration

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Ice Filtration

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I’m not sure if sitting watching a lump of ice slowly defrost over the course of an entire day quite counts as ‘cooking’ but ice filtration was a technique we used a lot in our last dinner. It is a slightly esoteric technique for clarifying any liquid, one that works really well and is ludicrously simple to do, but it does take a while.

With traditional egg-white clarification you would make your stock and then add egg whites and gentle simmer it all. The egg proteins form a ‘raft’ which captures all the impurities in the liquid. The most important of all these impurities is fat, because its presence in a liquid renders it cloudy – the fat droplets refract the light as it passes, leaving the impression of cloudiness.  This method relies on the network of gelatine strand to filter the impurities as it slowly melts. It needs to defrost in the fridge so that the temperature is low enough to leave the impurities trapped in the ice due to differences in melting points.

What you are left with at the end of the process is a clear, though not colourless, liquid. Initially it can seem slightly disappointing – it looks pretty insipid – but it packs flavour way beyond what you expect. Because the liquid isn’t simmering none of the flavour is lost into the air so you are left the pure essence of that stock.

Our method uses agar-agar which is really easy to get your hands on, it’s in most supermarkets. The example I’ve given here is to create a clear gazpacho, we used this in the last dinner and topped it with a toast foam. It went down an absolute storm so give it a go at your next dinner party. It also has the added benefit of looking like a tiny pint of beer when it has the foam on so it’s quite good fun.

The possibilities are endless. I wonder what ice filtered milk is like…

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The Method

Use 1.6g agar per litre of liquid to filter.

Get liquid and either add the agar and heat to 80-90c or if it is cold (you can do it with fruit juice or anything) just put the agar in water and heat it up to that temperature. This is to ‘activate’ the agar.

Chill and freeze.

Wrap the frozen block in muslin and leave in the fridge in the top of a steamer or something perforated so that the liquid can drip down.

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Our gazpacho, minus the toast foam

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Ice Filtered Gazpacho

  • 1½ lb (700 g) firm red ripe tomatoes
  • 4 inch (10 cm) piece of cucumber, peeled and chopped
  • 2 or 3 spring onions, peeled and chopped
  • 2 cloves garlic, crushed
  • ½ large red or green pepper, deseeded and chopped
  • 1 heaped teaspoon fresh chopped basil, marjoram or thyme (depending on what’s available)
  • 4 tablespoons olive oil
  • 1½ tablespoons wine vinegar
  • salt and freshly milled black pepper
  • agar agar (1.6g/litre)

Skin the tomatoes and cut out the seeds

Blend all ingredients and leave to macerate for at least 6 hours

Sieve

Heat to c. 40o and add activated agar

Once cooled, freeze

Strain in fridge through muslin

NB: yield will be significantly decreased after filtration

Bonus Toast Foam:

  • 8 slices of bread
  • 500ml water
  • 2tbsp butter
  • 2tbsp soy lecithin granules (get them from any health food store, it helps to stabilise the foam so it doesn’t break down)

Toast the bread

Simmer in the water along with the butter

Leave to stand for 30 mins

Strain through muslin, squeezing to extract flavour

Blend at full power with lecithin

Leave to stand

30-60mins before needed, pour into a large vessel (largest possible surface area) and whiz up surface with a hand blender to a foam

Leave to stand

Serving:

Pour soup into chilled shot-glass

Top with a head of foam

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