Cooking is science and tradition

Cooking is all about science. In this blog our chef Peter Coucquyt will give you insights in the chemistry going on in the kitchen...

maandag 21 februari 2011

Raisin-like caviar

In our post on osmosis we explained how the principle works and which changes occur in food. We also briefly mentioned that this phenomenon could take place on alginate caviar. If so what could we obtain?
Osmosis is the movement of water molecules through a selectively permeable membrane. The membrane is usually an intact cell membrane, present in many food products, but it can also be artificially created, e.g. when making alginate caviar. Water will move from an area of low solute concentration to an area of high solute concentration.
This is the reason why alginate caviar should be stored in the encapsulated fluid. In this case there is no difference in solute concentration so there will not be movement of water from or to the alginate capsule. When capsules are stored in pure water, the solute concentration in the capsule will be higher than in the storage liquid. So the capsules will take up water and swell, this will also dilute the concentration of solutes and the flavor in the capsule. This process goes on until equilibrium is achieved.
What if we now put the alginate caviar in salt or sugar?
Pickling products in salt or sugar was once a popular method. Salt and sugar extract moisture from the food, which increases the shelf life. The same will happen with the alginate caviar. The withdrawal of water from the fluid center of the caviar is an osmosis reaction. The result is a raisin-like caviar. Yet the caviar itself will not take up the sugar or salt. So the raisin caviar will not taste like the pickling fluid. Although the content of the caviar will be concentrated.
So now we know that by osmosis water can flow from the center trough the membrane. We just need to use a highly concentrated storage liquid, or even pure salt or sugar. What if we uses some energy like heat, could we than obtain the same results? 

pumpkin caviar in alginate bath

pumpkin caviar before drying

pumpkin caviar after drying

The results of the drying test are similar as pickling in salt or sugar, but faster. Drying till a fruit leather-like texture gives better results by pickling in sugar. Drying gives a tough result.

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