Types of Thickening Agents

Cornstarch

Cornstarch is the most common thickening agent used in the industry. It is typically mixed with water or juice and boiled to make fillings with a glossy semi-clear finish to products. Commercial cornstarch is made by soaking maize in water containing sulphur dioxide. The soaking softens the corn and the sulphur dioxide prevents possible fermentation. It is then crushed and passed to water tanks where the germ floats off. The maize is ground fine in a semi-fluid state and passed through silk screens to remove the skin particles. After filtration, the product, which is almost 100% starch, is dried.

In cold water, cornstarch is insoluble and granular, settling out if left standing. However, when cornstarch cooked in water, the starch granules absorb water, swell, and rupture, forming a translucent thickened mixture. This phenomenon is called gelatinization.

Gelatinization usually begins at about 140°F (60°C), reaching completion at the boiling point. The commonly used ingredients in a starch recipe affect the rate of gelatinization of the starch. Sugar, added in a high ratio to the starch, will inhibit the granular swelling. The starch gelatinization may not be completed even after prolonged cooking at normal temperature. The result is a filling of thin consistency, dull color, and a cereal taste. Withhold some of the sugar from the cooking step in such cases, and add it after gelatinization of the starch is completed.

Other ingredients such as egg, fat, and dry milk solids have a similar effect. Fruits with high acidity, such as rhubarb, will also inhibit starch setting. Cook the starch paste first and add the fruit afterward. In cooking a filling, about 3 1/3 lb. (1.5 kg) of sugar can be cooked with the water or juice for every 18 oz.(500 g) of starch used as a thickener. Approximately 4 oz. (100 g) of starch should be used to thicken 32 oz. (1L) of water or fruit juice. The higher the acidity of the fruit juice, the more thickener required to hold the gel. Regular cornstarch thickens well but makes a cloudy solution. Another kind of cornstarch, waxy maize starch, makes a more fluid mix of great clarity.

Pre-gelatinized Starches

Pre-gelatinized starches are mixed with sugar and then added to the water or juice. They thicken the filling in the presence of sugar and water without heating. This is due to the starch being precooked and not requiring heat to enable it to absorb and gelatinize. There are several brands of these starches on the market (e.g., Clear Jel), and they all vary in absorption properties. For best results, follow the manufacturer’s guidelines. Do not put pre-gelatinized starch directly into water, as it will form lumps immediately.

Note: If fruit fillings are made with these pre-cooked starches, there is a potential for breakdown. Enzymes in the uncooked fruit may “attack” the starch and destroy some of the gelatinized structure. For example, if you are making a week’s supply of pie filling from fresh rhubarb, use a regular cooked formula.

Arrowroot

Arrowroot is a highly nutritious farinaceous starch obtained from the roots and tubers of various West Indian plants. It is used in the preparation of delicate soups, sauces, puddings, and custards.

Agar-Agar

Agar-agar is a jelly-like substance extracted from red seaweed found off the coasts of Japan, California, and Sri Lanka. It is available in strips or slabs and in powder form. Agar-agar only dissolves in hot water and is colorless. Use it at 1% to make a firm gel. It has a melting point much higher than gelatin and its jellying power is eight times greater. It is used in pie fillings and to some extent in the stiffening of jams. It is a permitted ingredient in some dairy products, including ice cream at 0.5%. One of its largest uses is in the production of materials such as piping jelly and marshmallow.

Algin (Sodium Alginate)

Extracted from kelp, this gum dissolves in cold water and is used at a 1% concentration to give a firm gel. It has the disadvantage of not working well in the presence of acidic fruits. It is popular in uncooked icings because it works well in the cold state and holds a lot of moisture. It reduces stickiness and prevents recrystallization.

Carrageenan or Irish Moss

Carrageenan is another marine gum extracted from red seaweed. It is used as a thickening agent in various products, from icing stabilizers to whipping cream, at an allowable rate of 0.1% to 0.5%.

Gelatin

Gelatin is a glutinous substance made from the bones, connective tissues, and skins of animals. The calcium removed and the remaining substance is soaked in cold water, then heated to 40°C to 60°C (105°F 140°F). The partially evaporated liquid is defatted and coagulated on glass plates and then poured into molds. When solid, blocks of gelatin are cut into thin layers and dried on wire netting. Gelatin is available in sheets of leaf gelatin, powders, granules, or flakes. Use it at a 1% ratio. Like some of the other gelling agents, acidity adversely affects its gelling capacity. The quality of gelatin often varies because of different methods of processing and manufacturing. For this reason, many bakers prefer leaf gelatin because of its reliable strength.

Gum Arabic or Acacia

This gum is derived from various trees and is soluble in hot or cold water. Solutions of gum arabic are used in the bakery for glazing various kinds of goods, particularly marzipan fruits.

Gum Tragacanth

This gum is obtained from several species of Astragalus, low-growing shrubs found in Western Asia. It can be purchased in flakes or powdered form. Gum Tragacanthused is used to make gum paste and gum paste-wedding ornaments, but due to high labor costs and a prohibitive price for the product, nowadays is uncommon.

Pectin

Pectin is a mucilaginous substance (gummy substance extracted from plants), occurring naturally in pears, apples, quince, oranges, and other citrus fruits. It is used as the gelling agent in traditional jams and jellies.

Coagulation of Proteins

Coagulation is defined as the transformation of proteins from a liquid state to a solid form. Once proteins coagulate, they cannot return to their liquid state. Coagulation often begins around 100°F (38°C), and the process is complete between 160°F and 180°F (71°C and 82°C). During the baking process, the natural structures of the ingredients are altered irreversibly by a series of physical, chemical, and biochemical interactions. The three main types of protein that cause coagulation in the bakeshop are outlined below.

Egg proteins

Eggs contain many different proteins. The white, or albumen, contains approximately 40 different proteins, the most predominant being ovalbumin (54%) and ovotransferrin (12%). The yolk contains mostly lipids (fats), but also lipoproteins. These different proteins will all coagulate when heated, but do so at different temperatures. The separated white of an egg coagulates between 140°F and 149°F (60°C and 65°C) and the yolk between 144°F and 158°F (62°C and 70°C), which is why you can cook an egg and have a fully set white and a still runny yolk. These temperatures are raised when eggs mix into other liquids. For example, the coagulation and thickening of an egg, milk, and sugar mixture, as in custard, will take place between 176°F and 185°F (80°C and 85°C) and will start to curdle at 190°F and 194°F (88°C and 90°C).

Dairy and soy proteins

Casein, a semi-solid substance formed by the coagulation of milk, is obtained and used primarily in cheese. Rennet, derived from the stomach linings of cattle, sheep, and goats, is used to coagulate, or thicken, milk during the cheese-making process. Plant-based rennet is also available. Chymosin (also called rennin) is the enzyme used to produce rennet, and is responsible for curdling the milk, which will then separate into solids (curds) and liquid (whey). Milk and milk products will also coagulate when treated with an acid, such as citric acid (lemon juice) or vinegar, used in the preparation of fresh ricotta, and tartaric acid, used in the preparation of mascarpone, or will naturally curdle when sour as lactic acid develops in the milk. In some cases, as in the production of yogurt or crème fraîche, acid-causing bacteria is added to the milk product to cause the coagulation. Similarly, tofu is made from soybean milk coagulated with the use of salt, acid, or enzyme-based coagulants.

Flour proteins (gluten)

Two main proteins found in wheat flour are glutenin and gliadin (smaller quantities found in other grains). During mixing and in contact with liquid, these two form into a stretchable substance called gluten. The coagulation of gluten is what happens when bread bakes; that is, it is the firming or hardening of these gluten proteins, usually caused by heat, which solidify to form a firm structure.