2.1.1.b. Water and Colloid Chemistry

Colloid Chemistry

The foundation of the principles of how water functions from the physical and chemical standpoint in food preparation and cookery.

0°C (32°F)

At what temperature does water begin to freeze?

80 kcal/g

How much heat must be removed from 1 g of water during freezing?

540 kcal/g

How much energy is required to convert 1 g of water into steam?

100°C (212°F)

What is the normal boiling point of water?

Increases

What happens to the boiling point of water as altitude increases?

Surface tension

What causes the surface of water in a cylinder to form a concave meniscus?

Calcium and Magnesium

What minerals determines the hardness of water?

Ionization

Refers to the splitting of molecules into ions of opposite charge.

7

What is the pH of pure water?

Acid

A substance containing hydrogen that yields free hydrogen ions (H⁺) when dissolved in water.

Base

A substance containing the OH group that yields free hydroxyl ions (OH⁻) when dissolved in water.

Solution

Refers to the homogeneous mixture of the molecules or ions of two different substances, one of which is usually water (solute + solvent).

When the solvent can no longer dissolve additional solute, so adding more solute does not increase the concentration.

When does a solution become saturated?

Supersaturated Solution

Refers to a saturated solution that is prepared at an elevated temperature and then cooled without agitation.

Osmosis

Refers to the passage of water through a semipermeable membrane separating two solutions of different solute concentrations.

Degree Brix (°B)

Refers to a measure of sugar concentration that is numerically equivalent to percent sugar.

Osmotic drying

What food-processing technique uses concentrated syrup to draw water out of fruits by osmosis?

Sol

A colloidal system in which a solid is dispersed in a liquid, this is exemplified with gelatin in hot water and dilute starch in hot water.

Gel Point

The point during the sol-to-gel transformation at which the liquid begins to take on a semisolid character.

Emulsion

Refers to a mixture of at least two immiscible liquids, commonly oil and water in foods.

Oil-in-water

What type of emulsion is in milk, salad dressings, and mayonnaise?

Water-in-oil

What type of emulsion is in butter and margarine?

Emulsifying Agent

A compound with both polar and nonpolar groups, allowing it to be attracted to both phases of an emulsion.

Lecithin

What is the most common emulsifier found in egg yolk?

Foam

Refers to a dispersion of gas in either a liquid or a solid.

Aeration

Refers to the process of adding air into a food or beverage system, such as beating egg whites.

Viscosity

Refers to the resistance of a liquid or semisolid material to flow.

Fluidity

Refers to the inverse of viscosity and the tendency of a liquid to flow.

Lecithin

A compound that has lipolytic fatty acid chains and phosphoric acid that is hydrophilic, commonly found in egg yolks.