Last week we discussed air bubbles trapped in liquids. This week, let’s look at liquids trapped in solids. I’m talking about jellies.
There are two key ways to make an edible jelly: add gelatine (which is made from the collagen found in meat) or agar-agar (which is made up of the agarose and agaropectin polymers in seaweed, hence the name).
Now, here’s an interesting tidbit. Agar-agar is typically derived from red algae, a plant that is sometimes referred to as
Last week we discussed air bubbles trapped in liquids. This week, let’s look at liquids trapped in solids. I’m talking about jellies.
There are two key ways to make an edible jelly: add gelatine (which is made from the collagen found in meat) or agar-agar (which is made up of the agarose and agaropectin polymers in seaweed, hence the name).
Now, here’s an interesting tidbit. Agar-agar is typically derived from red algae, a plant that is sometimes referred to as China Grass; and that is why the boxed dessert that gels so easily when mixed with milk has that name. (I’d always wondered about that, as a kid.)
Back to jellies, both gelatine and agar-agar are made up of long-chain molecules that overlap, to form strong, continuous networks. When mixed in with a fluid, they reform these networks, turning a runny liquid into a jiggly dessert.
Collagen is prevalent in nature; it makes up about 30% of all protein mass in mammals. But it used to be much harder to extract. In trend-setting colonial England, the servants of the wealthy spent hours making it; which goes some way towards explaining the later American fascination with savoury gellos in bright colours and elaborate moulds.
Today, industrially manufactured gelatine is available as granules or as sheets.
Professional chefs prefer the sheets, since they are less likely to clump in water. But working with the raw ingredient is tricky. One must know exactly how much to use; which involves intricate calculations based on the bloom number of a sheet. This number, a scale from 30 to 300, was invented in 1925 by Oscar Bloom to indicate the gelling power of an agent.
All the technical details can overwhelm a home cook, which is why boxed dessert mixes are so popular. There, all the calculations are done for you.
Working with raw gelatine also takes longer. First, one must hydrate the sheet or granules by soaking them in water for about 10 minutes. Then, warm the liquid one wishes to gel, to 60 degrees Celsius. Stir the bloomed substance in until dissolved. And set the mixture in a refrigerator for 6 to 10 hours, to give the long protein chains time to bond.
The longer one keeps this mix, the firmer the jelly. In 10 hours, it’s a blob that melts in the mouth (and melts at room temperature). In 24 hours, it’s something one must gently chew.
Whatever one does, one must do it quickly, because gelatine loses its bonding properties even with ambient heat. The type made from meat melts at 31 to 34 degrees Celsius (depending on the animal). The variety made exclusively from fish collagen melts at about 25 degrees Celsius (which is why it is used to thicken dishes such as stews).
Agar-agar is much more durable. Here, the gelling power comes from long chains of carbohydrates, rather than proteins. The algae must be boiled, the liquid filtered and then freeze-dried to form this gelling agent, which is available as a powder, as strips or in noodle-like threads.
It too must be hydrated before cooking. The hydrated mix must come to a full boil in order for it to dissolve completely in water. Agar-agar sets at 38 degrees Celsius; it does not need a refrigerator. It does not melt again until it reaches 85 degrees Celsius, so it holds up well in, for instance, a buffet.
There are other gelling agents present in foods, but none as straightforward as these two. Carrageenan (also made from seaweed) and gellan (an industrially produced carbohydrate secreted by cultured bacteria) require far more processing. Alginates, another seaweed derivative, only gel in calcium-rich liquids.
Meanwhile, gelatine and agar-agar are so versatile, they’re hiding where you’d never expect them. They’re in gummy bears, of course, but also in marshmallows (for that stretchy property). They also help add texture to airy packaged foods such as whipped cream and flavoured yoghurt.
(To reach Swetha Sivakumar with questions or feedback, email upgrademyfood@gmail.com)
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