HFCS versus sugar

Sugar crystallizing on left, sugar plus lemon juice on right.
Sugar crystallizing on left, sugar plus lemon juice on right.

Ever since Michael Pollan mentioned HFCS  (High Fructose Corn Syrup)in The Omnivore’s Dilemma, everyone is sure that HFCS is quite evil. To try to understand it, let’s do a little kitchen experiment. You can do this one at home and it’s kind of fun.

We’ll start as if we were going make rock candy, by putting one cup of sugar in a saucepan with ½ cup of water and bringing it to a boil. Let it boil gently until all the sugar has dissolved.

Then pour half of the mixture into a small bowl like a custard dish. You could also use a small juice glass as along as it is heat resistant.

Now, add about 1 tsp of lemon juice to the remaining sugar solution and stir it in while you bring it back to a boil. Let it simmer for 30-60 seconds and remove it from heat. Pour this remaining sugar solution into a second small bowl. Let the two bowls set undisturbed for 24-48 hours.

When you look at the two bowls after this time, you will probably see large sugar crystals forming in the first bowl. The other will probably remain pure syrup with few if any crystals. This is exactly the experiment we did in the picture shown at the top of the column, and you will see large crystals in the left flask and no crystals in the right flask. The only difference is that we use these tall slope sided (Erlenmeyer) flasks so you could see the crystals better. Since there is very little evaporation from these flasks it took a couple more days for the crystals to form.

sucrose color
Sucrose structure. Glucose on left, fructose on right.

OK, now what is going on here?

Table sugar, also known as sucrose is actually made up of two smaller sugars: glucose and fructose. They both have the same formula, C6H12O6, but slightly different structures. (One has a 6-membered ring and the other a 5-membered ring.) After adding the weak acid in lemon juice, the two sugars come apart into the simpler sugars and the solution is no longer a single compound, but two quite different compounds which compete with each other and cannot crystallize because they are both there in equal quantities. The result is that the second dish stays a syrup and never crystallizes.

Sucrose split into glucose (left) and fructose (right).
Sucrose split into glucose (left) and fructose (right).

And what is that syrup? It’s 50% glucose and 50% fructose. This syrup is called invert sugar and is sometimes used in baking. It’s also pretty much the same thing as honey, which starts out as a sugar syrup, but the bees secrete the enzyme invertase which unzips it into glucose and fructose just as we did.

But wait a second! HFCS or High Fructose Corn Syrup is 55% fructose and 45% glucose, almost the same thing as this syrup. In fact, if you wanted to make it exactly the same as HFCS we calculate that you could do this by adding a teaspoon of Agave syrup, which is often about 90% fructose.

So, we just made a syrup which is identical to HFCS, except we made it from sugar instead of corn. Clearly this syrup is just about exactly the same as the sugar we started with, and perfectly safe to eat or cook with, (except that that trace of lemon juice might be just slightly perceptible.) So there is no major difference in sweetness nor in nutrition or caloric value. It’s still a flask of sugar syrup.

Corn Syrup

But hang it all, we didn’t make it from corn! How can it be the same as corn syrup. But it is. By the time we’ve gotten it to this form, it is just a couple of simple sugars and it really doesn’t matter where we got them from.

Corn syrup is made industrially from cornstarch, because this scales better for large batches. They start with cornstarch, which is actually just a long chain polymer of glucose units and unzip them using a simple enzyme, alpha-amylase. When you get done with this treatment you can get pretty much pure corn syrup out of the reaction, a solution of pure glucose, also sometimes called corn sugar.

The problem with glucose is that is isn’t quite as sweet as sugar is, and if you want to use it in cooking or baking you need to make it sweeter. Well it turns out that fructose, or fruit sugar, is sweeter than glucose, and a mixture of the two can mimic the sweetness of table sugar or sucrose.

If we had to go and isolate fructose from fruit juice, this would be an expensive process. But, it turns out that you can convert glucose (6-membered ring) in fructose (5-membered ring) by mixing it with the enzyme glucose isomerase. Then we can mix the glucose and fructose 45-55 to make HFCS. Why not 50-50? Well, once you unzip sugar into glucose and fructose, it isn’t quite as sweet and you need a bit more fructose to get the same sweetness as sugar.

So what’s our conclusion? If we can essentially make HFCS from table sugar it can hardly be dangerous. It’s the same thing as sugar and perfectly safe. And, incidentally, it doesn’t matter whether that sugar came from cane or beets: it is still a single pure compound. Sugar can easily be purified to a very high degree of purity since it crystallizes so easily and any traces of impurities from farming are removed during that purification. The same holds for cornstarch.

Oh, and if you are wondering where those two enzymes come from, you can get the common bacterium bacillus amyloliquefaciens  to make alpha-amylase, and the streptomyces flavogriseus bacterium to make glucose isomerase for you.

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2 thoughts on “HFCS versus sugar

  1. If sucrose can be split into glucose and fructose which then can’t be crystallized, how is it that honey, which exists in these forms quite readily crystallizes?

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