Water and Heat in Food and Food Preparation

Flashcards covering key vocabulary related to water and heat in food and food preparation, including properties of water, heat transfer methods, and food choices.

Factors Driving Food Choices

Quality and taste preference, convenience and time, social and eating context, economics, and health, all moderated by perception.

Beverages (Dietary Water Source)

Contain 95-99+% water, including milks, energy drinks, juices, coffee, tea, and clear broths.

Liquid Foods at Room Temperature (Dietary Water Source)

Contain 50-90% free water, such as ice cream, sorbet, yogurt, and jell-o.

Free Water in Solid Foods

Can be up to 70% of a food's water content, with produce being particularly high.

Metabolic Water

Water produced in varying quantities during the metabolic process where food is converted to ATP (energy), CO2, and H2O.

Water's Contribution to Foods

Contributes critical texture, shape, appearance, and flavor.

Turgor Pressure

The pressure exerted by water inside a plant cell against the cell wall, maintaining rigidity when the vacuole is full, or causing wilting when empty.

Water Dissociation

The constant breaking apart and re-forming of hydrogen-bonded clusters of H2O molecules, allowing water to act as an acid, base, or buffer.

Bipolar (Water Molecules)

Water molecules have one side with a negative charge and an opposite side with a positive charge due to the unique arrangement of hydrogen and oxygen atoms, leading to attraction between molecules.

Universal Solvent (Water)

Water's ability to bond readily with ionic compounds (like sodium) and to dissociate or hydrolyze other molecules (like starches and sugars), though it does not dissolve starch.

Affinity or Cohesiveness (Water)

Water molecules' tendency to form streams, droplets, and exhibit high surface tension due to strong intramolecular covalent bonds (between O and H) and intermolecular hydrogen bonds (between water molecules).

Surface Tension of Water

The cohesive forces between water molecules at the surface, which can be reduced by substances like detergent.

Detergent/Soap Molecule

Composed of a hydrophobic (water-hating) hydrocarbon chain tail and a hydrophilic (water-loving) ionic head (e.g., Na+).

Water Hardness

The presence of dissolved calcium and magnesium salts in water, which affects food cooking and interferes with surface tension; can be reduced by boiling or adding other salts.

Water's Cleansing Function

Water's ability to remove (dissolve) soil and microorganisms, enhanced when combined with detergent to reduce surface tension.

Colligative Properties of Water

Properties that depend on the concentration of solute particles, such as changes in boiling, freezing, and vapor pressure, which are influenced by heat, solutes, elevation, and atmospheric pressure.

Boiling (Water)

The phase change where liquid water's vapor pressure exceeds atmospheric pressure; influenced by solutes (raising boiling point), elevation (lowering boiling point), and pressure cooking (raising boiling point).

Lukewarm

A water temperature of approximately 98°F (37°C).

Scalding

A water temperature of approximately 150°F (65°C).

Simmer

A water temperature of approximately 185°F (85°C).

Boil (Temperature)

A water temperature of approximately 212°F (100°C).

Available Water (Aw) / Water Activity

Refers to the free, uncombined water in food, measured as the ratio of vapor pressure of water in the food to the vapor pressure of pure water; reduced by solutes and critical for microbial growth.

Bound Water

Water that is not available for microbial needs, often associated with food components.

Reducing Water Activity

An ancient method of food preservation that limits microbial growth by decreasing the amount of free water.

Water's Function in Hydrating/Blending

Water hydrolyzes/dissolves or dissociates sugars and ionic molecules, neutralizes acids/bases, and acts as a dispersing liquid for colloids like starches and calcium micelles.

Water's Function in Heat Transfer

An excellent medium for transferring heat, readily absorbing and releasing it due to its thermal properties.

Solutions (Dispersion)

Homogeneous mixtures with small particles (atoms, ions, small molecules) up to 1 nm that dissolve, showing limited light scattering and high stability (e.g., salt water, sugar water).

Colloids (Gels/Sols/Emulsions)

Heterogeneous mixtures with medium-sized particles (>1 nm, <1 micrometer) that disperse or dissociate but don't dissolve, moderately scatter light, and have unstable bonding (e.g., cheese, milk, mayonnaise).

Suspensions (Dispersion)

Heterogeneous mixtures with large particles (>1 micrometer) that are suspended, have high light scattering ability, and exhibit unstable or no bonds (e.g., uncooked starch in water, herbed salad dressing).

Conduction (Heat Transfer)

The direct transfer of molecular kinetic energy from one molecule to another, from regions of high to low temperature, influenced by a food's thermal diffusivity.

Convection (Heat Transfer)

The transfer of molecular kinetic energy by circulating air, water, fat, or steam as an intervening medium, resulting in more even and quicker heating.

Radiant Energy (Heat Transfer)

Energy waves that move very quickly to transfer heat; includes non-ionizing forms like microwaving, induction cooking, and broiling, where heat transfer to the food's surface is rapid.

Effectiveness of Heat Transfer Mediums

The ability of a medium (e.g., fat, water, steam, air) to readily transfer, retain, and slowly release heat; also influenced by pan reflectiveness in baking.

Induction Cooking

A method using a high-frequency electromagnetic source to induce heat in a magnetic cooking vessel, creating an alternating electric current in the pan that directly heats food by conduction.

Microwave Energy

Electromagnetic energy that causes molecules to spin, creating friction and heat; not absorbed by glass/ceramic/paper/most plastics, deflected by metal, penetrates about 2 inches, cooking deeper foods by conduction.

Microwave Effects on Food

Cooks high-water foods best; high-sugar and high-fat foods get very hot; prevents browning due to the absence of convection or radiant waves for surface heating or dehydration; less efficient for large quantities.

Non-ionizing Radiation (Microwave)

Lower-frequency electromagnetic radiation (like 2450 MHz microwaves) that causes molecules to vibrate and produce heat through friction, without damaging cells or ionizing molecular structure.

Ionizing Radiation

High-frequency, powerful, and penetrating electromagnetic radiation (e.g., X-rays, gamma rays, cosmic rays) capable of damaging living tissue, changing molecular structure, or causing mutations.