Cooking with chemistry: jellifying

Today’s bake is another one of those ‘things I thought you couldn’t make yourself’: jaffa cakes. These biscuit-sized cakes have caused much heartache on Bake Off as you have to get not only the base (the dreaded Genoise sponge, which doesn’t use raising agents but instead relies on suspended air in the batter) but also the jelly and the chocolate coating just right.

I used this recipe, but wanted to make mine veggie and replaced the gelatin with a mixture of carrageenan and galactomannan (in the form of Dr Oetker’s vege-gel).

Gelatin is derived froum a protein, collagen, that makes up many animals’ connective tissue. The long amino acid strands become interwoven when the liquid in which they are dissolved cools, making a gel. It is the ultimate gelling agent – even the word ‘gel’ comes from gelatine.

Since there’s still no non-animal-derived version of gelatin (though chemists are working on it), I opted for carrageenan, which is extracted from seaweed. Like agar, another common gelling agent and a favourite among microbiologists (not for eating but rather for growing bacteria on),  carrageenan is a polysaccharide. Unlike agar, some of carrageenan’s hydroxy groups are replaced with sulfate groups.

Dr Oetker’s vege-gel powder contains both calcium acetate and potassium chloride, a fact that puzzled me at first. I found out that different forms of carrageenan require different ions (calcium and potassium) to form a gel, so that makes a lot more sense.

carob tree seed pods
Carob tree seed pods (image by Felagund – Wikimedia)

The other gelling agent in the vege-gel is locust bean gum, another type of polysaccharide (galactomannan with a galactose/mannose ratio of 1:4). If you live in or have been to Mediterranean countries, you might have even seen the locust bean tree and its strange dark brown seed pods.

The jelly I got when using vege-gel was certainly more fragile and brittle than what I would expect gelatin jelly to be. But since I then hid it under a thick layer of chocolate, it didn’t really matter. I’d love to try out other gelling agents – maybe I’ll get my hands on some agar or arrowroot. Happy gelling!


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