Enzyme activity is a measure of the catalytic ability and there are two methods to measure enzyme activity: one of them is to measure the decrease in substrate concentration in a period of time, and the other is to measure the increase in concentration of a product after a period of time.Enzyme activity is usually the objective of growing bugs in a plant. Enzymes are biological catalysts. Just like other catalysts, they reduce activation energy, allowing reactions to proceed in a desired direction. Because their activity is dependent on the folding of a protein, they are usually sensitive to the temperature, pH, and salt concentration of the environment they work in. (Thus, pH, salt, and temperature are effective in preserving foods). There are exceptions to this, such as the enzymes put in washing powder (which come from bacteria evolved to survive in hot springs), but the general rule is that small deviations from their tolerable ranges can (reversibly) reduce activity. Larger excursions may denature them irreversibly.