By Erwin Waters
Sausage products that undergo extended treatment or storage will often show mold growth on the surface.
Molds can vary in color from white powdery molds, which on some dried sausage products is desirable-to green and black molds, which are undesirable.
For mold growth to occur, a product must first be exposed to mold or the spores of the mold and the environment for growth to occur. It is next to impossible to control mold cross-contamination because molds and spores are present everywhere, and they are easily carried in air streams.
Environment for mold growth
-- Food sources: The food sources for molds can be vegetable matter, carbohydrates or proteins.
-- Moisture: The moisture source can be from the product or the moisture contained in the air.
-- Temperatures: Molds can live and propagate at a wide temperature range, from minus 32 degrees F to 104 degrees F. The temperatures in a drying chamber-50 degrees F to 64 degrees F-are within the optimum range for mold propagation.
-- Oxygen: Molds that the meat industry is concerned with require oxygen to live and propagate.
Controlling mold growth
Because the fact that the entrance of molds into the ambient environment of the meat plant is impossible to eliminate, the best that can be done is to control those areas in the plant in which mold can propagate and increase the cross-contamination possibility.
Wherever there is sufficient moisture and food, mold can spread rapidly.
Refrigeration equipment drip pans are a prime example of where both mold and bacteria can propagate, and then be spread throughout the plant in the refrigerated air stream. The drip pans should be periodically cleaned and sanitized. Good daily sanitation practices are important in controlling mold contamination.
Without a sufficient amount of moisture present, molds and spores will not be able to adhere to surfaces, and propagation will not take place.
Molds require significantly less moisture to propagate than bacteria. When equated to water activity values (Aw), the following table illustrates the minimum Aw values that permit growth of some bacteria and molds:
To minimize the moisture available for the mold to grow, several factors need to be observed.
-- Surface temperature of the product: Whenever a meat product is releasing moisture to the air, the water evaporating from the surface of the product cools the product (evaporative cooling). In a drying chamber, the surface temperature of the product is closely related to the internal temperature of the product.
If the surface temperature of the product is at or below dew point of the air values, the moisture from the air will condensate on the product. Never put products in a drying chamber that are colder than the dry bulb temperature of the drying chamber.
If there is not a sufficient differential between the relative humidity and the Aw of the product's surface, moisture will not be able to evaporate in sufficient quantities to keep Aw value below 0.85.
-- Relative humidity of the air: The tool used to control the moisture content of the product's surface is the relative humidity of the air. A relative humidity of less than 79 percent will allow enough of the moisture from the surface of the product to be released into the air to keep the surface dry enough to attain the desired Aw value.
-- Air circulation around the products: The spacing of products from each other and the amount of positive air circulation around the total surface of the products plays an important part in mold control. Products that are too close to each other, or where the air circulation is not even, will allow moist air to be trapped between products.
-- Preventing case hardening at lowered relative humidity: At the start of the drying process, case hardening will not occur.
At later stages, if case hardening becomes evident, a two- to three-hour resting cycle every 12 hours-where all functions of the drying chamber are turned off-will allow sufficient moisture to migrate from the interior to the surface of the product to prevent over-drying of the surface.
Waters is senior consultant with Cook and Thurber LLC Food Industry Consultant Management Group. He can be reached at 407/391-2290, fax 407/391-1840; or 608/831-6958, fax 608/831-7101.