Dry matter

The dry matter (or otherwise known as dry weight) is a measurement of the mass of something when completely dried.

The dry matter of plant and animal material would be its solids, i.e. all its constituents excluding water. The dry matter of food would include carbohydrates, fats, proteins, vitamins, minerals, and antioxidants (e.g., thiocyanate, anthocyanin, and quercetin). Carbohydrates, fats, and proteins, which provide the energy in foods (measured in kilocalories or kilojoules), make up ninety percent of the dry weight of a diet. Water content in foods varies widely. A large number of foods are more than half water by weight, including boiled oatmeal (84.5%), cooked macaroni (78.4%), boiled eggs (73.2%), boiled rice (72.5%), white meat chicken (70.3%) and sirloin steak (61.9%). Fruits and vegetables are 70 to 95% water. Most meats are on average about 70% water. Breads are approximately 36% water. Some foods have a water content of less than 5%, e.g., peanut butter, crackers, and chocolate cake. Water content of dairy products is quite variable. Butter is 15% water. Cow's milk ranges between 88-86% water. Swiss cheese is 37% percent water. The water content of milk and dairy products varies with the percentage of butterfat so that whole milk has the lowest percentage of water and skimmed milk has the highest.

In the sugar industry the dry matter content is an important parameter to control the crystallization process and is often measured on-line by means of microwave density meters.

The nutrient or mineral content of foods, animal feeds or plant tissues are often expressed on a dry matter basis, i.e. as a proportion of the total dry matter in the material. For example a 138-gram apple contains 84% water (116 g water and 22 g dry matter per apple). The potassium content is 0.72% on a dry matter basis, i.e. 0.72% of the dry matter is potassium. The apple, therefore, contains 158 mg potassium (0.72/100 X 22 g). Dried apple contains the same concentration of potassium on a dry matter basis (0.72%), but is only 32% water (68% dry matter). So 138 g of dried apple contains 93.8 g dry matter and 675 mg potassium (0.72/100 x 93.8 g).

When formulating a diet or mixed animal feed, nutrient or mineral concentrations are generally given on a dry matter basis; it is therefore important to consider the moisture content of each constituent when calculating total quantities of the different nutrients supplied.

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