Thickening is a technique that utilizes the properties of starch, which absorbs water, adheres, and creates a smooth and glossy texture when heated and gelatinized. When a dish is nearly cooked, the prepared starch slurry is ladled into the pot to thicken the sauce, increase its adhesion to the ingredients, thereby enhancing the starchy texture and consistency of the dish's sauce, and improving its color and flavor.
The starch used for thickening, also known as starch powder, is a polysaccharide polymer formed from the condensation of multiple glucose molecules. The starches commonly used in cooking include mung bean starch, potato starch, wheat starch, and water chestnut or lotus root starch. Starch is insoluble in water, but when heated with water to 60°C, it gelatinizes into a colloidal solution. Thickening utilizes this property of starch.
Mung bean starch is the best starch for thickening but is rarely used. It is made by soaking, grinding, and precipitating mung beans. Its characteristics are strong viscosity, low water absorption, and a pure white color with a lustrous sheen.
Potato starch is the most commonly used starch in households today. It is made by grinding, washing, and precipitating potatoes. Its characteristics are strong viscosity, a fine texture, a pure white color, and a better sheen than mung bean starch, but it has poor water absorption.
Wheat starch is obtained by precipitating the liquid after washing bran from dough or can be made from flour. Its characteristics are a white color but a poor sheen, lower quality than potato starch, and it tends to precipitate easily after thickening.
Sweet potato starch is characterized by strong water absorption but poor viscosity and no sheen, with a dark reddish-black color. It is made by grinding, washing, and precipitating fresh sweet potatoes.
In addition, there are other starches such as corn starch, water chestnut starch, and lotus root starch.
Whether thickening is done properly greatly affects the quality of a dish, making it one of the fundamental skills in cooking. Thickening is often used in cooking techniques such as stir-frying, quick-frying, and sautéing. The common feature of these methods is high heat and rapid completion. Dishes cooked this way generally do not come with much sauce. However, due to the addition of certain seasonings during cooking and the water released by the ingredients themselves, the amount of sauce in the dish increases. Through thickening, the sauce becomes thick and coats the surface of the ingredients, thereby achieving a glossy, smooth, tender, and delicious flavor for the dish.