The science of thickeners

We all know that the success of any dish depends not only on flavour, aroma and colour, but has a lot to do with texture as well. The satisfying crunchiness of a crisp wafer, the voluptuous sensation of a creamy cheese sauce or the firmness of a morsel of well hung meat. This important parameter can often by adjusted by using what are known as thickeners. These are additional ingredients which, owing to certain chemical reactions, affect the consistency of our dishes, particularly when they are excessively liquid. And that’s not all: added thickness also has a significant effect on the look and taste of any dish, especially when it contributes to stabilizing emulsions.

Starches are the most widely known thickening agents and we often encounter them in recipes. They go under the name of corn starch, wheat starch or potato starch.

How do starches thicken

Starch is a compound made up of two molecules, amylose and amylopectin, in percentages of about 25% and 75% respectively. This structure is based on a dense network of bonds which, when in the presence of water and heat, break down and allow the amylose to trap molecules of water. This process results in jellification, or thickening, a technique widely employed in pastry-making to prepare custard creams, jellies and blancmange.

However, the results will vary according to the type of starch used. Corn starch, for example, is a proper flour, used as a thickener when we want to confer a translucent look to the dish. However, since it has quite a strong taste, it is preferable to use it in situations requiring very little cooking, taking care to dissolve it beforehand in a small amount of water to form a “paste”. If added directly to the dish it would form lumps that are practically impossible to get rid of. The same advice applies to potato starch, which has practically the same characteristics but performs better at low temperatures, for instance when having to thicken soups and sauces. In this case, however, you are advised to add the potato starch diluted in water when you have already removed the dish from the heat, without ever actually boiling the starch.

How much tapioca starch to thicken

Tapioca is considered to be the new frontier in the ambit of starch thickeners. It dissolves well without having to be diluted, it has an almost neutral flavour and excellent thickening properties, on condition that it is not used at excessively high temperatures, which would entirely neutralize the effect. Kuzu, the dehydrated and pulverized root of the eponymous plant is another excellent thickener, considered to be even better than tapioca. In fact, it has extraordinary thickening properties, with half a spoonful of this powder being sufficient to turn 250 ml of liquid into a jelly.

How to thicken without starch 

If you prefer not to use starch thickeners, there are plenty of alternatives. Of these, the most widely known is agar-agar. This is a jelly-like substance obtained from an alga which is widely used in pastry-making, since it is composed of sugar galactose molecules. It has good thickening properties and may also be used at high temperatures.

If, on the other hand, you need to jellify a liquid at low temperatures, it is preferable to use xantham gum, a linear polysaccharide structure made up of molecules of mannose, glucose and glucuronic acid. It can also be used for stabilizing emulsions, sauces in particular, together with pectin, another well known gelling agent based on the formation of an interlaced structure.

Finally, it is also worth remembering some protein-based thickeners which are cheap and effective. Collagen for example, obtained from meat broth, and egg yolk, on condition that it is used at a temperature of approximately 60°C, to prevent it from solidifying.