When dehydrating foods, using good sanitary practices is critical to reducing the risk of contaminating foods with pathogens and spoilage microorganisms:
- After harvesting produce or herbs, place in containers and locations that are free from additional contamination (for example, pets and wild animals will not have access).
- Begin the dehydration process soon after harvesting.
- Clean and sanitize all utensils, containers, the food-contact surfaces of dehydrating equipment, and work surfaces. To effectively clean, wash with warm, soapy water; rinse thoroughly with warm water; and sanitize using one of the following methods:
- Immerse utensils and drying trays in a chlorine bleach* solution (1 ½ teaspoons of bleach per gallon of water) for 10 seconds, then air dry (do not use a towel).
- Prepare a sanitizing spray solution of ½ teaspoon of household bleach per quart of water, and spray on food-contact surfaces. Let air-dry.
- Always wash hands before handling foods—that includes harvesting.
- Consider wearing disposable gloves when preparing foods for dehydrating. Wash hands before putting gloves on, and always remove gloves whenever you change a task (such as answering the phone or preparing another food item). If your gloves become soiled or torn during food preparation, replace them before resuming food preparation. Do not wash gloves to reuse—dispose of gloves after use. Gloves can give a false sense of security. Change gloves as recommended—do not contaminant food with gloves used incorrectly.
Drying is the world's oldest and most common method of food preservation. Canning technology is less than 200 years old, and freezing became practical only during the last century when electricity became more widely available. Food drying technology is both simple and readily available to most of the world's cultures.
The scientific principal of preserving food by drying is that by removing moisture, enzymes cannot efficiently contact or react with the food. Whether these enzymes are bacterial, fungal, or naturally occurring enzymes from the raw food, preventing this enzymatic action preserves the food from biological action.
Illnesses due to Salmonella and E. coli O157:H7 from homemade jerky raise questions about the safety of traditional drying methods for making beef and venison jerky. The USDA Meat and Poultry Hotline's current recommendation for making jerky safely is to heat meat to 160 °F and poultry to 165 °F before the dehydrating process. This step assures that any bacteria present will be destroyed by wet heat. But most dehydrator instructions do not include this step, and a dehydrator may not reach temperatures high enough to heat meat to 160°F or 165°F.
After heating to 160°F or 165°F, maintaining a constant dehydrator temperature of 130°F to 140°F during the drying process is important because:
- the process must be fast enough to dry food before it spoils; and
- it must remove enough water that microorganisms are unable to grow.
Research findings support what the Hotline has been recommending to callers. Additionally, safe handling and preparation methods must always be used, including:
- Always wash hands thoroughly with soap and water before and after working with meat products.
- Use clean equipment and utensils.
- Keep meat and poultry refrigerated at 40°F or slightly below; use or freeze ground beef and poultry within 2 days; whole red meats, within 3 to 5 days.
- Defrost frozen meat in the refrigerator, not on the kitchen counter.
- Marinate meat in the refrigerator. Don't save marinade to re-use. Marinades are used to tenderize and flavor the jerky before dehydrating it.
- Steam or roast meat to 160°F and poultry to 165°F as measured with a food thermometer before dehydrating it.
- Dry meats in a food dehydrator that has an adjustable temperature dial and will maintain a temperature of at least 130 to 140 °F throughout the drying process.
Dehydrating or Drying Fruits, Vegetables, and Herbs
To maintain safety and quality, several factors must be considered when drying fruits, vegetables, and herbs. Keep in mind that specific food products often have recommendations that are unique to them.
Drying removes the moisture from food so that microorganisms such as bacteria, yeasts, and molds are less likely to grow; however, drying does not effectively destroy them. Because there is not a heat treatment that effectively destroys disease-causing microorganisms, it is critical to use safe food-handling practices when growing and handling fruits, vegetables, and herbs for drying.
The optimum drying temperature is 140°F. If higher temperatures are used, the food will develop "case hardening" and moisture will not be able to escape from the food; this, in turn, will lead to a moldy food product. Therefore, do not rush the drying process.
Low humidity is also needed when drying foods. If the surrounding air is humid, the foods will not dry effectively. Increasing the air movement away from the food will assist in the drying process.
Foods can be dried in the oven, under the sun, on the vine, or indoors using a dehydrator. There are several resources that provide tested methods for dehydrating vegetables, fruits, and herbs—ask your county Extension office for information on specific drying methods.
Packaging and storage: dried foods are susceptible to insect contamination and moisture reabsorption; therefore, it is important to store immediately in a package that does not allow the foods to reabsorb moisture. Vacuum packaging is a good option. Also, pack in smaller quantities so that the contents are consumed all at once—this avoids the need to reopen the package and expose the contents to air and moisture.
-Joan Hegerfeld-Baker, SDSU Extension Food Safety Specialist