Accuracy in Measurement Background information
A utensil used to make a precise measurement of any substance is referred to as a measuring device. The best measuring devices for liquids have handles and pouring spouts. When filled to the highest graduation, liquid cups hold the volume designated; i.e., one CUP, one pint, one quart, etc., and have a space above the highest graduation so the liquid does not overflow.
Solids are best measured in cups that are the size of fractions on a graduated liquid measurement cup or device. That is, a 1/4 measuring cup holds the same amount as 1/4 cup graduation on a liquid measuring device. The cups the size of fractions allow leveling and parking of nonliquid (dry) ingredients. The results, again, are a more precise (accurate) measurements.
Precision, Mathematics, Measurement, and Food Science Scientists try to use the measurement device that is most precise for the characteristics of the substance being measured. Sometimes quantities of material are measured by mass and sometimes by volume. For example, an ice cube is a rectangular solid. Volume and mass each refer to the amount of space it occupies. One way to measure the volume is to measure the length, width, and height of the cube, then multiply the length x height x width.
Another way to measure the volume of the cube would be to let it melt and measure the volume of liquid in a graduated cylinder. A graduated cylinder is more accurate than a beaker and might be more accurate than a measuring cup. It is easy to obtain the volume of a liquid because once the liquid is poured into the cylinder, the volume is the level the liquid reaches as indicated by the measurement marked on the sides of the container. If a liquid that forms a meniscus is measured, the volume is read from the bottom of the curve formed. Volume is estimated to 1/10 of the smallest division on the scale.
Mass can be measured with a number of different instruments. One often used by scientists is a triple beam balance. There are two kinds: a low-form or a high-form. Both are referred to as a balance. ("Show and Tell" the balance beam).
To use a balance, it must be zeroed correctly. It has 3 riders: 100 g, 10 g, and 1 g. The mass of any object on the balance is the sum of the values of the 3 riders. To mass (weigh) an object, simply add the total of the 3 riders.
In many school laboratory and home situations, food is massed and the volume measured by using kitchen scales and standardized measuring cups. The accuracy of these tools can be checked using more precise tools (cylinders, balances, etc.) manufactured for scientific lab work.
Basic Principles
1. A recipe is a formula that produces a specific product.
2. Recipes are easier to reproduce when both the originator of the recipe and the person duplicating it use standardized measuring devices and methods.
3. Solid foods are affected by particles that settle, crystal composition that allows air spaces in the matter, air that is or can be added, and packing from shaking or pressing the particles. In liquid foods, meniscus (a film that can form on the surface of some liquids, such as syrup) sometimes forms. It distorts the surface of the liquid and interferes with accurate measures. Any of the above can affect the weight/volume in measuring.
4. In confectioner's sugar, the crystals are finer than in ordinary table sugar, and in brown sugar the crystals are larger. In cake flour and self-rising flour, other ingredients are added. Hydrogenated shortening and lard differ in composition of crystals. All of the above make differences in weights and volume that make adjustments necessary in substituting different forms of the same ingredient.
5. With every measurement made or repeated for an ingredient, accuracy decreases. It is important, for accuracy, to use the measuring utensil closest in size to the desired unit of measurement.
6. Measurement utensils used in food preparation should be checked against standard devices because new ones might not hold a standard volume. If a utensil shows variation from the standard of more than 5%, do not keep or use it. Variance in measuring usually affects a recipe adversely.
Formula for calculating deviation:
% deviation from standard weight = ((Standard weight - average weight)divided by Standard weight)x 100