Acid: In a chemical sense, the opposite of a base. When an acid is mixed with water, the solution (which is consequently acidic) has a pH below 7. Acids have a sour taste.
Amino Acids: Amino acids are organic chemical compounds that can form chains, or polymerize, into larger molecules. Proteins consist of long chains of amino acids.
Amylase: Enzymes that can cleave starches into simple sugars such as maltose and glucose. In plants, amylases break down starch into sugar that plants in turn use for growth and energy production. Amylases occur in saliva and are an important part of the digestive system in humans.
Antioxidant: Chemical compounds that prevent oxidation of other compounds. In food, antioxidants are used to prevent the oxidation of fat. In biological systems, antioxidants inhibit processes caused by oxidative stress, among others associated with a number of diseases.
Aroma: Related to sensation of odorant molecules, olfaction, sensed by the scent receptors in the nose. A requirement for a compound to have aroma is that it is volatile. It must be able to evaporate to reach the nose either through the nose (nasal cavity, called orthonasal olfaction) or through the oral cavity (mouth, called retronasal olfaction).
Ascorbic Acid or Vitamin C: One of the water-soluble vitamins. In food manufacturing, ascorbic acid and its salts are used as additives to inhibit oxidation reactions that lead to food spoilage (additive codes 300 ascorbic acid, 301 sodium ascorbate and 302 calcium ascorbate). Ascorbic acid is found naturally in many fruits and vegetables.
Astringency: A sensation in the mouth, mouthfeel, often described as an astringent or drying sensation. It is sometimes mistakenly referred to as a taste, but is formally not one of the basic tastes. Common foods and drinks with astringent character are black tea, red wine, grape skin/seeds, unripe bananas, etc.
Base: Chemically, the opposite of acid. Previously, the term “alkaline” was used for basic substances. A base will react with acids in a neutralization reaction. Basic substances have a pH higher than 7. Few foods are basic, but some examples are soda, egg white in old eggs, and the Nordic speciality “lutefisk” (stockfish, preserved dried whitefish, commonly cod, which is “reconstituted” to resemble fresh fish by soaking in lye solution).
Biochemistry: The branch of natural sciences that studies chemical substances and processes occurring in living organisms.
Carbonate: A negatively charged ion (CO32-), which is a part of many naturally occurring salts. Occurs in chemical reactions with carbonic acid (carbonated drinks), carbon dioxide gas, and hydrogen carbonate (bicarbonate), such as the chemical leaveners baking powder and baking soda.
Coagulation: A stronger and irreversible change of proteins compared with denaturation. May be caused by heat, acidic, or basic conditions, or by reaction with enzymes. In coagulation, the long protein molecules react with each other and can form three-dimensional networks in the food. This way, for example a raw egg that is a solution of proteins in water, the networks transform into a gel where water is bound in a network of coagulated proteins. See also, denaturation.
Collagen: Fiber-forming protein, and the most important building block in connective tissues such as cartilage, tendons, and veins/arteries.
Condensation: Phase change of a substance from gas to liquid, such as when water vapor (steam) condenses to liquid water. It is important to note that phase changes, such as condensation and evaporation, are not the same as chemical reactions because during phase change the substance is not changed into new substances. During condensation, much energy is released, so condensation is a heat transfer mechanism in cooking. This comes in addition to the three basic forms of heat transfer; conduction, convection, and radiation.
Conduction/thermal conduction: Heat transfer between a material of higher temperature with another of lower temperature where the two are in direct physical contact. One of the three basic forms of heat transfer (in addition to convection and radiation).
Conductivity: Intrinsic property of a material that represents its ability to conduct heat (or electricity).
Continuous phase: See dispersion, consisting of non-miscible phases forming an even mixture. In a dispersion, the dispersed phase is distributed evenly in the continuous phase. Thus, the continuous phase surrounds small droplets, bubbles, or particles that form the dispersed phase. Examples of continuous phases are the water phase in whipped cream (liquid foam), the water phase in mayonnaise or Hollandaise sauce (oil-in-water emulsions), and the fat in chocolate (dispersion where cocoa- and sugar particles are distributed in cocoa butter).
Convection/thermal convection: Heat transfer in a gas or liquid where material of higher temperature moves to an area of lower temperature. One of the three basic forms of heat transfer (in addition to conduction and radiation).
Cooking loss: Weight loss as a result of cooking (heating) of food, usually meat and fish. Occurs mainly as result of evaporation and drainage of water. Cooking loss is usually given as percentage value.
Denaturation: Mild, reversible or partially reversible, change/modification of structure of proteins. Denaturation can occur when proteins are heated, react with acids or bases, or react with enzymes. Denaturing can also occur by means of mechanical action, such as when whisking egg whites. Denaturation is closely related with coagulation, which is a stronger and irreversible change in proteins for the same reasons. See also, coagulation.
Diffusion: A phenomenon whereby molecules are randomly spread/distributed in a gas or liquid as result of their constant thermal motion. In a gas mixture or solution, substances will gradually be distributed evenly as a consequence of diffusion.
Dispersed phase: See dispersion, consisting of a dispersed phase and a continuous phase. The dispersed phase is the one evenly distributed in the continuous phase. Examples of distributed phase are gas bubbles in a bread (foam), oil droplets in mayonnaise (oil-in-water emulsions), and fruit pulp floating in fruit juice (suspension). See also emulsion, foam and gel.
Dispersion: A mixture of substances that are not miscible where one component is evenly distributed in the other. Examples of dispersions are emulsions (one liquid distributed in another), gels (a liquid distributed in a solid), and foams (gas distributed in either a solid or liquid) are examples. See also, dispersed phase and continuous phase.
Dry matter: The proportion of a food that is not water. For example, the proportion of water in a cucumber is around 96%. The proportion of dry matter is thus 4%, only marginally higher than in sea-water (3.5%).
Elastic: A property of a material where it resumes its original shape spontaneously after being deformed (stretched or compressed). Often used in relation with the term plastic. Examples of elastic materials and objects are rubber bands, inflated balls, and a well-developed gluten network.
Emulsion: An even mixture of one liquid into another in which the two liquids are not miscible, for instance oil and water. With the aid of an emulsifier, it is still possible to achieve relatively stable, even mixture: an emulsion. Emulsion is an example of the more general term dispersion. In the kitchen, we have oil-in-water emulsions, where oil is evenly distributed but not dissolved in water (mayonnaise, Hollandaise sauce), or they may be water-in-oil emulsions where water droplets are evenly distributed in oil/fat (butter, margarine).
Enzyme: Biological catalyst, a compound that accelerates biochemical reactions in cells. Chemically, enzymes are a subgroup of proteins. Enzymes require certain conditions to function. They can contribute to food decay but can also be utilized in cooking and food manufacture. The most important factors affecting the enzyme’s functions are heat, salinity and pH.
Ester: A category of organic compounds closely related to organic acids (carboxylic acids). The aroma in many fruits and flowers is due to organic esters.
Evaporation: Phase transition from liquid to gas. Although evaporation is most rapid when the liquid boils, it is worth noting that it takes place at almost all temperatures, albeit at different rates (for example, water boils at 100°C but will still evaporate slowly at room temperature).
Falsify: To disprove. Usually used in relation to research, and commonly associated with the philosopher of science Karl Popper, who wrote that hypotheses cannot be proven, only falsified. “Scientifically proven” is thus an unscientific statement. The hypothesis that stands despite all attempts at falsifying it, is often considered the most plausible explanation. When putting forth an explanation, the researcher should therefore strive to make the hypothesis testable, i.e. falsifiable.
Fermentation: Transformation of substances by means of microorganisms. Examples of fermented foods are cheese and other sour milk products, beer and wine, various fermented fish (still-present ancestors of gravlax, e.g. Icelandic hákarl, Norwegian rakfisk, or Swedish surströmming), fermented vegetables such as kimchi and sauerkraut.
Flavor: Complex experience consisting mainly of the sense of taste (in the mouth) and olfaction/smell (in the nose). Other perceptions, experienced through the trigeminal nerves (pain, heat, cooling) and texture are also considered part of, or contributing to, flavor.
Foam: Foams are special cases of dispersions in which a gas is evenly distributed/dispersed in, or surrounded by, a liquid or solid. The gas is always the dispersed phase in a foam. Examples of solid foam are raised breads and cakes, foam rubber, Styrofoam, and meringue. Examples of liquid foam are whipped cream, raw meringue (whipped egg whites), whipped sauces, and cappuccino foam.
Gel: A gel is a special case of dispersion where a liquid is bound, evenly distributed, in a solid. Liquid is the distributed phase and the solid is the continuous phase. Examples of gels are jello, cucumber, cheese, and meat. Jello is a “pure” gel; the others are more complex mixtures but can also be seen as gels.
Gelatinize: Take up liquid to form a gel. An example is starch granules that absorb water.
Gliadin: One of the proteins found in, among others, wheat grain, and together with glutenin forms gluten in pastries, breads, etc. In order for gluten networks to form, glutenin and gliadin must interact with each other. Gluten is a so-called protein complex of the two proteins.
Glucosinolate: Compounds with certain nitrogen and sulfur groups. Present in some plants, they function as defense mechanism against animals and insects. When the plant cells are damaged, they come into contact with enzymes, subsequently liberating pungent tasting/smelling substances. While possibly harmful for humans and animals, they can, in low concentrations, have medicinal properties. They also have desirable flavor characteristics, such as the pungent sensation from mustard, horseradish, wasabi, radish, and certain varieties of lettuce and cabbage.
Gluten: A plastic and elastic network built up of glutenin and gliadin proteins, providing flexibility in doughs with wheat flour. The gluten network makes it possible to produce pasta and raised pastries, breads, etc.
Glutenin: One of the proteins found in, among others, wheat, which together with gliadin forms gluten. See also gliadin and gluten.
Half-life: The time it takes for half the amount of a compound present in a chemical reaction to be consumed. It is one of the measures used to describe the rate of chemical reactions (and for decomposition of radioactive materials).
Heat: A process where heat energy is exchanged between an area or object with higher temperature and another having a lower temperature.
Heat capacity: The property of a material/substance to store thermal energy. The specific heat capacity is the inherent property per quantity of the material, where the unit is J/(kg K). That is, the energy it takes per kg of material to increase its temperature by one Kelvin (or °C).
Hemicellulose: Long-chain molecules (polymers) consisting of between 500 and 15,000 sugar molecules. Hemicellulose is related to cellulose and, together with cellulose and lignin, one of the constituents of the cell walls in plants. Hemicellulose can react with acids and bases. In basic solution it may dissolve, which results in the food to be cooked (or overcooked) quicker.
Hydrophilic: “That which loves water.” Property of substances that make them attract water, or are miscible with (soluble in) water. In a chemical sense, this is related to the term polarity; hydrophilic compounds or groups within a compound are usually polar or ionic. Hydrophilic is often set up as contrast to hydrophobic, that is water-repellent properties. Examples of hydrophilic substances are water-soluble substances such as sugar, salt, and alcohol (ethanol).
Hydrophobic: “That which fears water.” Properties of substances that make them repel water and, therefore, are not miscible with water. In a chemical sense, this is related to the term polarity; hydrophobic compounds or groups within a compound are usually non-polar. Hydrophobic is often set up as contrast to hydrophilic. Examples of hydrophobic compounds are non-water soluble/miscible substances such as oil and fat. The term is often related to the term lipophilic, “that which loves fat.”
Inhibitor: A substance that inhibits chemical or biochemical reactions.
Ion: Atom or molecule with electric charge (positive or negative). Ions form salts. All substances built up by ions will have both positively and negatively charged ions in a way so that the sum of charges balances one another (charge balance).
Kelvin: (K) Basic unit for temperature used in scientific contexts. The Kelvin scale has the same relative magnitude as the Celsius scale (one degree Celsius equals one Kelvin, relatively). While 0°C is defined as the temperature for which pure water melts/freezes, 0 K is defined as the lowest possible temperature attainable, absolute zero which is -273.15°C.
Lipophilic: “That which loves fat,” substances miscible with fat. Lipophilic substances are usually not miscible or soluble in water. The term is often linked with the term hydrophobic, and used as opposite to hydrophilic.
Maillard reaction(s): A reaction sequence between sugars and amino acids by which color, taste and aromas develop. The Maillard reactions may proceed slowly at low temperatures, but the rate increases radically when the temperature rises to around 140°C. Examples of foods where the Maillard reactions play an important role are bread (brown crust), roast/fried meat (browning of the surface), coffee (during roasting), fudge/caramel, and dulce de leche (due to reaction between lactose and milk proteins during extended boiling).
Micelles: Spherical particles formed when soap molecules, with their hydrophilic and hydrophobic/lipophilic parts, arrange themselves to surround fat droplets, usually in water. The lipophilic parts align toward, and into, the fat droplets while the hydrophilic parts face the surrounding water. This way, the micelles can follow the water when formed in the encounter between fat, soap, and water during dishwashing.
Microorganisms: Common designation for microscopic living organisms that include yeasts, molds and bacteria. Enzymes are chemical substances (proteins) and are therefore not microorganisms.
Molecules: Among the smallest parts of chemical compounds. Molecules consist of two or more atoms.
Mouthfeel: The experience, most often of food or drink, in the mouth that is not directly associated with taste (the “basic tastes,” sweet, sour, salty, etc.) or olfaction/smell. Mouthfeel is usually related to texture, viscosity, smoothness, chewiness, crispness, hardness, graininess, juiciness, etc.
MSG/glutamate: Abbreviation of monosodium glutamate. MSG is the sodium salt of an an amino acid called glutamic acid. MSG is found naturally in various foods and raw materials, but is also used in its pure form as an additive (additive 621, in Europe E621). It acts as a flavor enhancer and provides umami flavor.
Multisensory: That which is related to the simultaneous sensation by multiple senses (taste, sight, olfaction/smell, audition/hearing, touch). Related to the concept modality/sensory modality, where a modality is the experience from one of the senses. Eating is a multisensory experience that involves all five senses.
Myosin: Muscle protein involved in contraction of muscle cells. Consequently, it is also a component of meat, and plays an important role in the structure and texture of meat before and during cooking, and when enjoying (or not enjoying) meat.
Non-polar: Used about substances and molecules. Most easily explained as an opposition to polar, in which a molecule has a charge (is an ion) or has an uneven distribution of electrical charge. A non-polar compound will normally not be miscible with or soluble in water. Non-polar compounds are often fat soluble. A good pair for association is water colors (containing polar pigments) and oil paint (containing non-polar pigments).
Octahedron: A geometric structure, a polyhedron, with eight faces. For reference, a cube is also a polyhedron, but with six faces.
Olfaction: Formal term for the sense of smell.
Pectin: Long-chain molecule (polymer) that acts as one of the building blocks in the structure of plants. Metaphorically, one may say that pectin is the glue that holds the cells in the plant together. It is also present in cell walls, and if the cellulose molecules are seen as the reinforcing bars in the cell wall, the pectin can be seen as the cement. Pectin is abundant in the peel from apples and citrus fruits. It is also found in berries but is broken down during ripening. Pectin is used in food and cooking as a gelling agent.
pH: A quantitative measure of how acidic or basic/alkaline a water solution is. A neutral solution has a pH of 7, an acidic solution has a pH below 7 and a base has a pH above 7. The pH scale ranges from 0-14, although it is possible to have solutions with a negative pH and pH greater than 14.
Phase/State of matter: See state of matter.
Plastic: A property described as a material being irreversibly deformed upon pressure. Often seen in relation with the term elastic. An example of a plastic material that is not elastic is clay or play dough. A good bread dough is both plastic and elastic.
Polarity: A property of molecules that describes how charge is distributed as a result of the distribution of electrons and electrical charges within the molecule. For example, water is a polar molecule: the area around the oxygen atom is partially negatively charged and the area around the hydrogen atoms is partially positively charged. Ions and salts are by nature highly polar. By contrast, charge and electrons in non-polar molecules are more evenly distributed. Polarity is a fundamentally important notion in chemistry, and the foundation (among others) for substances being hydrophilic and hydrophobic.
Precipitation: When a substance is converted from water-soluble to insoluble, or when two water-soluble substances react to form an insoluble product. Examples are the coagulation of proteins (a substance is converted from water soluble to insoluble) or the reaction between tannins and proteins to give a precipitate during cooking of stock (reaction between two soluble substances to give a third, insoluble one).
Protease: Common designation for enzymes that break down, or cleave, proteins.
Protein: An organic compound consisting of a long chain of amino acids. Proteins can also be composed of more than one chain that are more loosely bound to each other. Proteins, together with fats and carbohydrates, are among the basic nutrients.
Radiation: See thermal radiation.
State of matter/Phase: A concept describing the physical state of substances. Common states of matter, or phases, are gas, liquid, and solid. Some other states of matter also exist, like plasma and supercritical phase, but these are not commonly encountered in food (although the former can actually be achieved in a an ordinary microwave oven and the latter is used in food industry when supercritical CO2 is used to remove caffeine from coffee to produce decaffeinated coffee).
Solution/dissolve: Mixture of substances in a liquid phase. The dissolved substance may be a gas, another liquid, or a solid. Examples are sugar or salt dissolved in water, vinegar in water, color or flavorings in oil, carbon dioxide in water (e.g. sparkling). If the substance is completely dissolved, the solution will be completely transparent, but it may still have color. A cloudy or misty solution indicates that it contains some undissolved material, but it can still be a solution since some substances may be dissolved while others are not. To dissolve is not the same as to melt (which is the phase transition between solid and liquid).
Surface tension: A physical surface phenomenon that causes a water surface to behave like a flexible membrane. It is the reason why a needle can float on water or insects may walk on water. Surface tension is also the phenomenon behind capillary forces, that plants (including tall trees) can draw up water through thin capillaries so that the water reaches the whole plant. The reason for the surface tension is weak chemical bonds between water molecules, and between water molecules and other surfaces.
Suspension: An even mixture of two non-miscible substances in which the distributed phase is a solid and the continuous phase is a liquid. One example is orange juice (as opposed to transparent apple juice, which is a solution). Suspension is a special case of dispersions. There also exist solid–solid suspensions, where a solid is distributed in another solid, such as solid chocolate where cocoa and sugar particles are dispersed in solid cocoa fat.
Tannin: Chemical substances (polyphenols) in plants. Tannins react with proteins in precipitation reactions (forming precipitates), during cooking as well as in the mouth. In food and drinks, tannins can give the mouthfeel experience called astringency by reacting and binding proteins in the saliva. This is the dry feeling experienced when drinking certain red wines, strong tea, or biting into a grape stone or skin. Also, tannins may react with proteins during cooking, e.g. when heating meat stock with red wine. In plants, the presence of tannins functions as a protection, as it prevents the plant from being eaten by certain animals and insects.
Taste: One of the five senses (the others are olfaction/smell, sight, audition/hearing, and touch). Taste is, as olfaction, among the chemical senses where the signals to the brain occur as result of chemical substances interacting with taste receptors on the tongue and elsewhere in the mouth.
Thermal energy: The energy of a substance, system or object possesses due to its temperature.
Thermal radiation: In cooking contexts, electromagnetic radiation, usually in the form of infrared radiation, is one of the three basic forms of heat transfer (in addition to conduction and convection). Heat can also be transferred via microwave radiation, which has a somewhat different mechanism from infrared radiation.
Umami: One of the “basic tastes,” together with sweet, salty, bitter, and sour (there are probably a number of other such tastes as well). Umami is often referred to as the fifth taste and can be described as rich and brothy. MSG, monosodium glutamate, is among the substances with a distinctive taste of umami. Umami can be experienced as a naturally present taste in many foods, or can be introduced or enhanced by addition of e.g. MSG.
Viscosity: A property of a substance (usually liquid or gas) that describes its ability to withstand flow. It can be associated with how “thick” a fluid is or how easily it flows. Low viscosity means that the substance flows more easily (gases have very low viscosity, water has low viscosity among liquids) while high viscosity means that it flows slowly (honey has high viscosity compared to water).
Water Activity: A numerical value between 0 and 1 that indicates the amount of water in a food that is is not chemically bound to any ingredient, and thus available to microorganisms. For example, the use of salt and sugar for preserving food is based on the fact that these ingredients result in reduced water activity, and thus making the food a “dry desert” for microorganisms that will consequently not thrive and multiply.