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Sensual, aromatic and appetizing, not only doing sauces enhance our food, but it can also teach us a lot about the close bond between cooking and science. Let’s start from a consideration that may initially sound banal: sauces have to be velvety. Some sauces do have an uneven consistency, but the most popular ones are those that seem to caress the palate.
A sauce, in almost all cases, is an emulsion, meaning a mixture of two or more liquids that tend to separate. For example, vinaigrette sauce is composed of oil and vinegar: tiny drops of vinegar dispersed in oil produce a sauce that looks smooth and even but which, after a few minutes, will start to separate.
Is it possible to make an emulsion more stable or more fluid? Certainly, so long as you become familiar with a few scientific notions. You have to know that in an emulsion, the liquid transformed into droplets is known as the “dispersed phase”, while the liquid surrounding the droplets is the “continuous phase”. Our palate is more aware of the tactile sensations produced by the second liquid, while the first adds sharp aromatic notes, such as acidic flavours. You may wonder why mayonnaise is so velvety and stable. This is because oil constitutes the continuous phase while lemon provides the dispersed phase.
The Power of Emulsifiers
The problem with most emulsions is that sooner or later they are subject to the phenomenon of “coalescence”: the tiny droplets of the dispersed phase gradually unite to reconstitute the original liquid and separate from the continuous phase. The greater its propensity to coalesce, the less velvety the sauce will be. To solve this problem, we need to use an “emulsifier”.
This is a substance that stabilizes the relationship between the dispersed and continuous phases. In the specific case of mayonnaise, this substance is lecithin, a phospholipid contained in egg yolk. Phospholipids are two-tailed molecules: one bonds well with water-based liquids, while the other repels them. So, the trick is to add egg yolk to a vinaigrette sauce: the phospholipid tails that are soluble in vinegar – a water-based liquid - dissolve, while the others create a sort of barrier. This results in the vinaigrette being inverted: it is no longer composed of tiny droplets of vinegar dispersed in oil, but its exact opposite. In this way, we achieve a twofold effect: a more stable and attractive sauce combined with a more delicate flavour.
Egg yolk, which must be used raw and extremely fresh, is a very powerful emulsifier, but not the only one. Mustard, for instance, contains a polysaccharide that is blander than lecithin and confers an aromatic note that is more distinctive than that of egg yolk. Corn starch also works well as an emulsifier but it acts differently: it thickens the mixture and makes the particles of the dispersed phase more immobile, helping to prevent coalescence.
The Perfect Vinaigrette
Now that you are keen to put what you have learned into practice, why not try this quick yet highly scientific recipe for a fantastic vinaigrette sauce. A sauce that is smooth, even after several minutes, velvety and delicious. So much so, that your friends will find it hard to believe this is a simple vinaigrette!
To make it, you will need half a shallot (finely chopped), half a spoon of mayonnaise, half a spoon of Dijon mustard, one spoonful of wine vinegar, one teaspoonful of salt, three spoonfuls of extra virgin olive oil and a pinch of pepper. Mix all the ingredients thoroughly, apart from the oil. Now add the oil gradually in a trickle, using a fork to whip up the mixture. Success is guaranteed, especially if you use it to serve a fantastic pinzimonio (raw vegetable dip) or as an original sauce for accompanying grilled meat.