Gels and Jellies: Why They Do What They Do

Molecular Lesson 1

I’m going out on a limb here but I’m planning to attempt to present a new food and science related topic once a week, if nothing else than as a way to make my posting more regular. Hopefully it’ll force me to do a little more regular learning as well. As is evident by my erratic posting, this may be more difficult than making a sand souflee rise, but we shall see.

In anticipation of playing with some gelatin and agar later this week, I decided to do some research on the subject of gelatins. As is the case with many things, all my life I’ve been using gelatin but have never taken the time to really even question the mystery of how it works. It’s another one of those cooking wonders that we just accept for what it is and move on, using it regularly but never quite knowing how or why it does what it does. Usually I always reach for Harold McGee’s book but lately I’ve been reading Herve This’s Kitchen Mysteries
and I’ve been learning a lot of good stuff from it.

While you’re simmering your stock for hours, extracting flavorful marrow from bones, you are also extracting the element within the connective tissue that allows us to create gels, jellies, aspics, etc (which is what gives your stock body). Anyone who has made a good stock has seen it stand up straight and rigid like a bowl of Jell-O after cooling in the fridge. There are a number of places from which we can derive the substances necessary to create gels and jellies. Collagen in the bones of our hoofed friends is the most common but we can also extract pectin from many fruits and there’s even a substance in seaweed that has very similar capabilities. Extracting these tiny bits of connective structure and then utlizing them to add body to our sauces, thicken our gels and solidify our jellies and aspics is a pretty amazing process.

For now we’re going to focus on gelatin derived from animal bones (which is esentially the same or very similar to the gelatin you’ll find in packets or sheets). The protein that makes up much of the connective tissue (and skin) is called collagen. Collagen molecules are long and rigid, like fibers. They are responsible for meat becoming tough when it’s overcooked. How do we get them to soften and release instead of stiffening up? By heating the collagen molecules slowly at a low temperature, they are allowed to relax and their bonds begin to release. Collagen molecules are structured like a chain – when we allow them to relax like this, the links of the chain can begin to slip apart. Just heating them alone doesn’t do much for us, but when we heat these molecules in the presence of water, the water molecules are allowed to slip in between the links of the chain and create a solution. When the mixture cools, the collagen molecules stiffen back up but now they’re surrounding water molecules too so we have… voila, a gel!

My interpretation of what’s happening:

There’s a lot more techincal stuff going on in the background but, on the surface, that’s a basic explanation. Now that we (sortof) understand what’s going on when this transformation is taking place, we can look at a couple of the variables affecting the structure of the final gel. Two important factors are:

  • a) the rate at which gels are cooled and
  • b) stability while cooling

a. By cooling slowly, we can actually achieve a stronger final structure because we allow those molecules to slowly and carefully recombine around the water molecules. If we quickly chill our gels, the strands don’t have time to intertwine as carefully as they would when cooling slowly and the structure will not be as strong as it could be.

b. You were always taught when making Jell-o that you should leave it in the fridge untouched (assuming your mom taught you proper Jello-ing technique). But why? Does moving the cooling gel really affect how it solidifies? Yes. As those molecules are cooling and reconnecting, they are fragile. If we shake them as they’re trying to carefully reconnect their bonds, we break them apart and affect their ability to form properly. Eventually the gel will form but the bonds will be weaker and it will take much longer to complete.

Hopefully you learned something from this and aren’t annoyed that there were no pretty pictures of food. I promise there will be some fun gelatin-related dishes on here soon…

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2 Responses to Gels and Jellies: Why They Do What They Do

  1. Stefanie says:

    haha i love the graphics. especially the “relaxed” molecules.

  2. Stepfanie says:

    The unwinding molecules look terrified.
    I like your blog. :) Can’t wait to read more fun with gelatin.

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