Wednesday, April 25, 2007

Not So Simple Syrup

It's been a while folks, but I have a few drinks backlogged that I will get to very soon. But basically the problem is that it's very difficult to train for a triathlon and drink often. There must be room for both somewhere, so I'll squeeze them both in somehow.

Anyway, to follow on the simple syrup stuff from Alton Brown's show, I've been thinking about simple syrup chemistry. Turns out there's a lot more going on than just dissolving some sugar into water.

First of all is the concept of "water activity". I happen to work at a place that employs a food scientist, and she introduced me to the term while we were discussing the possible shelf life of reconstituted peanut butter powder.

Water activity is basically the amount of water that is in a substance that isn't immobilized or chemically bound. High water activity means fast spoilage, low water activity means slow spoilage. Bacteria and fungi need water, and therefore high water activity, to live and reproduce. From Wikipedia, "Bacteria usually require at least 0.91, and fungi at least 0.7". Wikipedia's list of common foods' water activities show that raw meat and milk with .97 or so water activity leads to quick spoilage, but honey or dry pasta at only .5 will stay good for a long time.

This is where sugar comes in. Sucrose (a disaccharide, made up of glucose and fructose) is a small molecule, and really good at binding up that free water. You can make a sugar syrup by just dissolving table sugar (sucrose) in water, like the commenter in the previous entry said, by pouring boiling water into a bowl of sugar. But you aren't really getting the water activity low enough to prevent spoilage without refrigeration. You can try adding more sugar than water, but at some point you're either going to get a syrup that's too thick, or run the risk of super-saturating the solution and ending up with rock candy in the bottle. What to do?

Monosaccharides like glucose and fructose are smaller than glucose, and are even better at reducing water activity. So if you were making simple syrup, you'd probably want that sucrose, which is made of glucose and fructose, to break up, right?

Turns out there are two super-easy ways to do it: for a 1:1 sugar/water solution, add a pinch of cream of tartar along with the sugar to the boiling water. Or a bit of lemon juice. (1 gram of acid per kilogram of sugar) Acid is a catalyst to breaking up those sucrose molecules into fructose and glucose. You have to simmer for 20 minutes for the reaction to totally finish, but the resulting syrup will have a lower water activity than a sucrose solution, as well as being about 20% sweeter. This stuff is called an partially inverted sugar syrup, or invert syrup for short. The "invert" part is about how it polarizes light, if you must know.

You can also make a partially invert syrup without acid by changing the recipe from a simple syrup (1:1) to 2:1 sugar/water, and simmering for 5-7 minutes until the solution is clear. The result will be a bit thicker since there is more sugar solute.

This stuff can sit out on your bar for a good six months. Although you'll probably have used it up by then, anyway.

I'm definitely going to try the acid version, as my pourers have a hard time with the thick 2:1 that I've been using. Here's to chemistry!