The food lab better home cooking through science ( PDFDrive ) 955

easily mix to form a homogeneous mixture In cooking, this most often occurs with oil and water (and, for all intents and purposes, vinegar or lemon juice can be considered water, as they behave in the same way) You can put them in a container together and stir them up, but eventually, like cats and dogs, they will separate and stick with their own kind There are a couple of ways around this The first is to disperse one of the two—the oil, say—into fine-enough droplets that water can completely surround them Kind of like putting a single cat inside a ring of dogs—there’s no way for it to escape and rejoin its feline friends A common example of this kind of emulsion is homogenized milk, in which whole milk is forced at high pressure through a fine screen, breaking up its fat molecules into individual droplets that are suspended in the watery whey This is called an oilin-water emulsion, because the fat molecules are separated and completely surrounded by water molecules Most familiar culinary emulsions are of this type, the most common exception being butter, which is a water-in-oil emulsion: tiny drops of water are completely suspended in butterfat (of course, once you incorporate that butter into a hollandaise sauce, you’ve converted it into an oil-in-water emulsion; see here for more on hollandaise) Simply mixing oil and vinegar forms an extremely unstable emulsion—no matter how thoroughly you mix them, no matter how much you separate the oil molecules, eventually they regroup and your emulsion will break In order to form a stable emulsion, you need to add an emulsifying agent known as a surfactant Remember that cartoon CatDog? The one with the head of a cat on one end and the head of a dog on the other? Well, CatDog is kind of like a surfactant: he’s got something that’s attractive to both cats and dogs, which makes him a kind of feline-canine ambassador, allowing the two to mix together a little more easily Culinary surfactants are molecules that have one end that is attractive to water (hydrophilic) and one that is attractive to oil (hydrophobic) Common kitchen surfactants include egg yolks, mustard, and honey, and it’s easy to see the work of a surfactant in action The container on the left contains oil and balsamic vinegar mixed in a ratio of 3:1 The one on the right has the same ingredients, with the addition of a small amount of Dijon mustard Both containers were sealed and shaken vigorously until the vinaigrette looked homogeneous I then allowed them to rest at room temperature for 5 minutes As you can see, the vinaigrette without the mustard separated much more rapidly than the one with mustard At this point, you’re probably thinking what I’m thinking: this is all very neat, but what difference does it make to my salad? Good question  ... easy to see the work of a surfactant in action The container on the left contains oil and balsamic vinegar mixed in a ratio of 3:1 The one on the right has the same ingredients, with the addition... until the vinaigrette looked homogeneous I then allowed them to rest at room temperature for 5 minutes As you can see, the vinaigrette without the mustard separated much more rapidly than the one with mustard... allowing the two to mix together a little more easily Culinary surfactants are molecules that have one end that is attractive to water (hydrophilic) and one that is attractive to oil (hydrophobic)