Clarification: Filtering with agar

Written on May 26th, 2013 by Michael

Clarifying liquids is one of the core techniques in haute cuisine. The goal is to remove even the smallest particles from a liquid, thus making it perfectly clear. Classically, this is done for a consommé by adding meat, mirepoix, tomato and egg white to the broth. A body forms from the denatured proteins of the meat and the egg white, aided by the acidity of the tomatoes. This floating raft binds the particles and pulls them to the surface, where they can be carefully removed. This procedure is technically complicated, and is particularily used to create clear soups.

Here, we describe another technique that relies on the physical properties of agar gels. We can use this technique everywhere where we want to remove floating particles as gently and taste neutral as possible, and where a regular sieve, chinois or coffee filter just wouldn’t cut it. The use of this technique in modernist cuisine goes back to an experiment by Dave Arnold, the Director of Culinary Technology at the French Culinary Institute in New York. Agar-Agar is a polysaccharide (that means it consists of complicated sugar chains) which is produced from red algae. That makes it nearly neutral in taste (very highly concentrated agar gels smell a little bit like the sea, but are usually too concentrated for practical use) and also vegan.

This technique works because agar gels exhibit syneresis: This means that the liquid at cut surfaces of the gel has the tendency to weep out. If we now prepare a relatively weak gel and cut it into very small pieces, a large proportion of the liquid will be able to seep out. The floating particles, however, will be held back in the agar matrix. This technique doesn’t work for all hydrocolloid gels, iota carrageenan does not exhibit syneresis, and can’t be used for this.

Ingredients:

  • Liquid to be clarified
  • Agar powder (available in good supermarkets, health stores or asia shops)
  • Sieve and cheesecloth to filter

Procedure:

  1. A liquid is gelled into a weak (0.2-0.3% agar/total weight) agar gel. To this end, the liquid (or parts thereof, see hints) must be heated above 80°C. The agar powder is added and the liquid is stirred for 5 minutes at the same temperature. This allows the agar to hydrate (the polysaccharide chains can unfold).
  2. Let the liquid cool completely. Below 40°C gelation sets in.
  3. Cut liquid with a whisk into small curds.
  4. Use gravity to drain liquid from the gel through a cheesecloth. The particles are bound in the gel, the filtrate is clear.

Nützliche Tips und Tricks

  • Never squeeze out the cheesecloth. This causes agar pieces to pass through. Should this have happened, try to use a paper coffee filter to remove the pieces.
  • Best results are obtained when you let the liquid drain slowly, over night. If necessary, gently massage the filter bag with a hand to loosen the gel.
  • Hot and acidic liquids can hinder or prevent the gelling of the liquid. To circumvent this problem, dissolve and hydrate the agar in 1/5 of the liquid or water and then add back to the rest of the liquid. It’s important that the liquid is above 40°C after addition of the concentrated agar solution, otherwise premature gelling can set in.
  • The same procedure is useful to clarify sensitive liquids, like fruit juices, since they don’t need to be warmed.

Anwendungsbeispiele

  • Clarification of orange juice after Dave Arnold:
    Mix 250g cold orange juice with 1.5g agar. Bring to a boil and let simmer for 5 minutes. Add 500ml of cold orange juice to the mixture and let gel on an ice bath.
    Cut gel into curds with a whisk and pass through a cheesecloth. Every now and then, lift the cloth and massage carefully.
    If necessary, return gel to a bowl and cut up more with a whisk, continue filtering
    750g juice can yield around 500g of crystal clear juice.
  • House Tonic
    In multiple attempts to prepare our House Tonic recipe, agar clarification has proved the only viable method to remove the small floating cinchona bark particles from the infusion
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