therefore more efficient at thickening, than wheat flour.
Potato starch differs from these grain starches because the starch is derived from the plants root or
tuber. The starch grains are larger, and they absorb more water and release starch at lower
temperatures. Also, their amylose molecules are much longer than in grain starches, so are more
effective at thickening. Due to their ability to thicken fairly quickly, they are often added to correct
sauces at the last minute – they thicken quickly and do not need pre-cooking in a roux to improve their
flavour (unlike the starch in wheat flour which has a very floury taste and is usually pre-cooked to
improve its taste). However, because potato granules are more fragile, they are more easily broken
up, so a sauce thickened with potato starch will thin more easily. To improve the dispersion of the
potato starch in the sauce, preventing lumps, the starch is often pre-mixed with butter to aid dispersion
in the sauce as the butter melts.
All these thickening agents however, need to be heated to thicken. This limits their use to sauces that
are not affected by heating. Fresh herb purees, and gazpacho, for example, cannot be thickened by
these agents without cooking the preparation, which has led to an increased interest in cold effective
thickeners, including the alginates and the gums.
As explained previously, most gelling agents, in certain conditions, will act as thickeners. For example,
alginates, in the absence of calcium, will act as a thickener. A small quantity of alginate (0.4 %) will
thicken a sauce without the need for heating, however very strong mixing is required to dissolve the
alginate, which is fairly time consuming. If the preparation is not sufficiently mixed, the alginate
molecules may join together and form lumps giving the sauce an undesirable texture.
Recently, a family of compounds called gums became popular. These are derived from plants and are
generally complex carbohydrates made of different sugar molecules. They are used as thickeners,