What is a Syrup?

Quite simply it’s a flowing mixture of sugar and usually at least a little water. That water is partly responsible for the fact that most syrups, despite their sugar concentration, don’t crystallize easily. But there’s usually something else in there that inhibits crystallization, a little something called invert sugar. Invert sugar is a term that gets tossed around quite a bit in cooking and baking circles, about as much as “caramelization” and “Maillard reaction.” But what is it exactly?

Basically, invert sugar is a mixture of sucrose (25%) and its two component sugars, glucose and fructose (75%). Invert sugar exists in nature but is usually made by humans for various culinary and scientific applications. You get it by making a mixture of sucrose (table sugar) and water, then heating it and adding an acid. In the kitchen that acid can be lemon juice, tartaric acid, vinegar or any number of others.

The effect of heat and acid on sucrose is that it splits the molecule into the above mentioned mixture, and once that’s done it not only won’t re-form as sucrose, it will remain a liquid. As for why, this is the point at which my own understanding starts to break down. All I know is that for some reason fructose won’t form crystals when it’s in the presence of both glucose and sucrose. Organic chemists in the audience, please feel free to weigh in here.

As for why invert sugar is called invert sugar, I do know that. Put on your physics hat and join me here.

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14 Responses to What is a Syrup?

  1. candide says:

    I’ve fallen in love with invert sugar. Its anti-crystallization properties do wonders for ganaches, jams, sorbets, and it gives moistness to cakes and pastries. It also lets you avoid corn syrup. I now keep a large jar of it in my frig at all times and incorporate it into more and more of my baking. Here’s the recipe I’ve been using for several years.

    http://www.chefeddy.com/2009/11/invert-sugar/

  2. Henry says:

    I always wondered why many sorbets recipe ask for boiling water and sugar to make a syrup. I thought, why didn’t they just puree the fruits with the sugar? Would that be easier? I guess the invert sugar has anti-crystallising properties? But then I didn’t recall there being an acid in the syrup – do water and sugar only suffice to make an invert sugar?

    • joepastry says:

      Hi Henry!

      Invert sugar does indeed have anti-crystallization properties, though they’re not as necessary in ice cream since water crystals are obviously the greater concern. As for why you simmer the sugar and water without acid I can’t say for sure. Obviously to dissolve it and probably to thicken it to at least some degree. I’ll mull that over!

      - Joe

  3. Erin says:

    I’m not an organic chemist, but my guess is the question “What does optical rotation have to do with crystal formation?” might be worth asking.

    Maybe.

    Interesting subject!

    • joepastry says:

      I wish I knew the answer to that, Erin. I only play a scientist on TV. But I’ll see what I can dig up!

      - Joe

  4. Antuanete says:

    Fascinating! Never knew about that invert sugar thing. Is it added to every bottled syrup, including those that claim to be molasses syrup? And what about maple syrup – does it contain invert sugar or just has enough water to keep it from crystallization?
    Btw, below was a discussion about beet sugar and that beet molasses isn’t used in culinary. Actually, I have jar of “sugar beet syrup” at home, whatever it means; it doesn’t specify whether it’s made from beet molasses or beet sugar, but maybe in Germany (syrup comes from there) they have figured out, how to remove undesirable flavors from beet molasses.

    • joepastry says:

      Hey Antuanete!

      I meant to say that beet molasses is used in Europe, just not here in the States. As for invert sugar and syrup, that’s all coming up!

      - Joe

  5. nemo says:

    I think the main reason why adding inverse sugar prevents crystallization is that its presence reduces the purity and concentration of the sucrose, making it harder for the sucrose molecules to find each other and make crystals. In my experience as a chemist-in-training, the more pure your solution of something is, the more likely you’ll get nice crystals of it.

  6. Christine says:

    Here is a nice website that talks about sugar and sugar crystallization in different candies: http://www.exploratorium.edu/cooking/candy/sugar.html

    Some chemistry behind sugar crystals: Crystallization of fructose and other saccharides is essentially an ordered way to pack the molecules together. When you have lots of molecules of different shapes and sizes you disrupt the ability to create the ordered crystal structure. You also have the presence of the acid which acts as a catalyst to break up the bond that links fructose and glucose together. The acid also disrupts the hydrogen bonds between sugar molecules (hydrogen bonds help the sugar crystallize).

    Hope that helps!

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