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rendered bacon fat) Avoid using bacon fat for more delicate things like vegetables or fish Q: I’ve heard that if you fry fish in oil, it can make the oil smell fishy Any truth in that? At one point or another, you’ve probably walked into a restaurant or perhaps a neighbor’s home and immediately caught a whiff of rancid, fishy-smelling oil You may even have said to your host (or if you are more restrained than I have been in the past, to yourself), “Oof, somebody frying fish in here?” Well, here’s the thing: I’ve got both a fried fish shop and a fried chicken shop right on my block in Harlem Oddly enough, it’s the fried chicken joint that smells like rancid, fishy oil, while the fried fish shop smells only of fresh seafood What gives? Turns out that the “fishy oil” smell you get from fried foods has nothing to with the fish itself; it’s caused by the inexorable breakdown of fat molecules Q: Hang on a minute Breakdown of fat molecules? Sounds to me like you’re talking about oxidation and hydrolysis Can you explain yourself? No problem Remember high school biology, where we learned that a fat molecule is made up of three fatty acids attached to a glycerol backbone, all arranged in a large upper-case-E shape? Well, the problem is that these fat molecules are not exactly stable Given exposure to oxygen and enough time, they break down And this gradual breakdown is sped up by exposure to heat, light, and air Unfortunately, when you fry, all three of these types of exposure occur in abundance On its own, exposure to oxygen causes oxidation, a process that causes the large fat molecules to break down, resulting in many smaller molecules, among them ketones and short-chain fatty acids These are the foul-smelling molecules that are the true cause of that fishy smell in fry shops, and this type of reaction occurs even when you don’t add any food to the hot oil In extreme cases, it can even occur in poorly stored bottles of oil (for this reason, you should never store your oil near the stove—you’re simply inviting rancidification) Once you actually start frying things, it gets worse Hydrolysis, a reaction that occurs when you combine water, oil, and heat (i.e., fry something), compounds and speeds up the effects of oxidation That’s why oil used for frying eventually breaks down and becomes stinky and unusable Depending on how hot you fry and how much food you fry at a time, a container of oil will get anywhere from a half dozen to a few score of uses before it becomes unusable Finally, the last way in which oil breaks down is a process called saponification—literally, the conversion of oil to soap, and when we say soap, we’re not talking Ivory or Dove bars, we’re talking about the chemical definition: a chemical salt of a fatty acid.‡ Soaps are a surfactant, which means they have a hydrophobic (oil-loving/water-hating) end and a hydrophilic (water-loving/oil-hating) end They are the peacemakers of the oil and water world, allowing the two to coexist without separating, as they are wont to do In this case, though, peaceful coexistence is a bad thing: the more surfactants your oil contains, the more water it can ... chemical salt of a fatty acid.‡ Soaps are a surfactant, which means they have a hydrophobic (oil-loving/water-hating) end and a hydrophilic (water-loving/oil-hating) end They are the peacemakers of the oil and water world, allowing the two to coexist without separating, as they are wont to do... occurs even when you don’t add any food to the hot oil In extreme cases, it can even occur in poorly stored bottles of oil (for this reason, you should never store your oil near the stove—you’re simply inviting rancidification)... stove—you’re simply inviting rancidification) Once you actually start frying things, it gets worse Hydrolysis, a reaction that occurs when you combine water, oil, and heat (i.e., fry something), compounds and speeds up the effects
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