MadSci Network: Biochemistry

Subject: Why does cream of tartar stop the crystallisation of sucrose?

Date: Thu May 29 15:24:40 2008
Posted by Julian
Grade level: 10-12 School: Städt. Gymnasium Schmallenberg
City: Bad Fredeburg State/Province: NRW Country: Germany
Area of science: Biochemistry
ID: 1212099880.Bc

Why I'm asking? I'm planning to make crashglas with sugar (which should be
glas-like, not crystalline) and I'm asking myself why in the recipe I found on
the internet there's cream of tartar on the list.
You already answer a similar question: "What is the chemical ester mimicking
the" by L Menkin. But my question is slightly different.

Ions, which means, salt (I tried it with NaCl), cause the molten sugar not
crystallize. But NaCl also causes the sugar glass to become milky and less
transparent. Other ions have the same effect, which is why you should use
destilled water to get a clear result.
As the ions don't allow the sucrose-molecules to build a regular grid because of
their electrostatic field, it is obvious why the sucrose doesn't crystallize.

But where does that milky look come from? And why doesn't that effect show up
when I use cream of tartar? I mean, after all it consist of ions.
Is the cream of tartar really building esters with the sucrose, which can
inhibit the crystallisation (because of the hydroxyl-groups?)?

I already know that the tartaric acid (as every other acid) causes the sucrose
to split into fructose and glucose. These different sugars are also causing the
sucrose not to crystallize.

So why do ions inhibit the crystallisation process? Where does that milky-white
look come from? And why doesn't the effect show when using cream of tartar?

I would be glad to know what's going on in my kitchen, really! ;)

Re: Why does cream of tartar stop the crystallisation of sucrose?

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