Category Archives: Frying

The down side of freshness

Regular commentator Hans writes in to ask:

So what’s this about food not browning well in really-fresh oil?

I’m glad you asked that, Hans! For indeed people who really know frying will tell you that perfectly clear, fresh oil doesn’t cook food particularly well. That’s very true. The question is: why? The answer, again, is because oil and water don’t mix. Fry oil with no soaps in it is held so far at bay by outrushing a steam that it never comes into contact with the food. That doesn’t mean that the food doesn’t get heated all the way through, but it does mean that it doesn’t get brown and crispy (or at least not very). The solution: add a little soap (and by that I mean old cooking oil) to the pan. It doesn’t take much, just a couple of teaspoons to two or three quarts of oil, to do the job.

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How long have I got, doc?

How long does it take for good fry oil to turn bad you mean? That depends on a number of factors, chief among them the type of fat you’re using. In general, you want one that’s fairly stable (i.e. resistant to breakdown) and neutral flavor-wise. For me that means either vegetable or canola oil. Solid fats like shortening or lard are even more resistant to breakdown, but are less convenient for the home fryer.

Assuming you don’t fry a whole lot of food at one time, you should get half a dozen uses out of a single pan full of oil (you’ll have to replenish some of course, since the food will soak some of it up). But use your nose. If the oil looks dark and/or has that telltale fishy ketone smell, dispose of it. You can do what I do and pour it out in a remote corner of the yard, or put it into disposable vessel and put it in the trash. Under no circumstances put it down the drain. Even liquid fat is hell on pipes.

Another important tip: if you want to re-use oil, don’t fry in an uncoated cast iron pan. Exposed iron acts as a catalyst that speeds up oil breakdown by many orders of magnitude. I know, grandma made fried chicken in that big cast iron pan you have. There’s no reason to break tradition, just don’t expect to use the oil again afterward.

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All About Frying II

To understand how the ’76 Steelers can turn into the ’08 Lions, we need to back up a bit and talk about fat composition. Kitchen fats are what are known as trigycerides. Which is to say their molecules are made up of three long-chain fatty acids attached to a “backbone” of glycerol. Imagine a capital letter “E” and you get the idea.

The trouble with these nice orderly fat molecules is that they don’t stay orderly, especially when you expose them to air, water and heat (as in oh, say, a fryer). In such an environment, they steadily, inexorably break down.

The reactions that cause fat molecules to break down are of two basic types: oxidation and hydrolysis. Oxidation, which occurs as the oil is heated and exposed to air, causes the fatty acid chains to break into pieces, yielding all kinds of weird compounds including foul-smelling short-chain fatty acids and ketones (the things that make old oil smell like fish).

Hydrolysis results from the combined effects of heat and water (introduced to the equation by food). It causes the fatty acid chains to break off the glycerol backbone, resulting in free fatty acids and glycerol. If the environment happens to be alkaline (which it becomes as bits of food are cooked and/or burned) a further reaction takes place: saponification.

Now, as some of you may remember from an old post on potash, saponification is the process by which fatty acids, in the presence of an alkaline, are converted into fatty acid salts. In other words: soaps. So now we’ve got soap molecules mixed in with the frying fat. And what does soap allow oil and water to do? Anyone? Anyone? Yes, you in back with the KFC. Right, it allows them to mix. Now we have a fry environment in which fat and water molecules can slip right past each other. And that, my friends, is what turns the ’76 Steeler defensive line into the ’08 Lions. Not a pretty picture for a doughnut. Not pretty at all.

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All About Frying I

In order to excel at things like doughnuts, fritters and cannoli, it’s important to understand the process of frying. As I’ve mentioned previously, good frying is really more like steaming, but why would that be so? It all comes down to this simple maxim: oil and water don’t mix.

In the case of frying, the oil is, well, the oil. And the water? That’s the food. Actually it’s the batter that’s around the food, or in the case of cake doughnuts, the batter that is the food. Batters, you see, contain a lot of water, and that’s critical to frying. Immerse a battered, oh, let’s say sausage in a fryer and you’ll see quite a lot of activity. Try the same thing with an unbattered sausage and well, it’s a lot less fun.

The reason: when liquid water is suddenly immersed in 375-degree fat it turns instantly to steam. That steam wants to escape the confines of the food, and it does so in the form of bubbles. As the steam exits the food it does something critically important: it keeps the fat — which wants to get into the food — out. It’s like a game of football. The offensive line is the fat, the defensive line is the steam. If your oil is nice and fresh, your defense is like, say, the ’76 Steelers. When the play starts there’s a lot of grunting and mashing, but in the end the offense doesn’t really get anywhere. The result is perfectly cooked food that absorbs a bare minimum of fat.

But if your oil is old and broken down, it’s a whole different ball game, so to speak. The offense rushes over the defense like the Green Bay Packers over the Detroit Lions, and well…you’re probably better off ordering pizza. More information on oil breakdown (and fewer compounded metaphors) in the next post.

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