Ensuring Food Safety in Produce Drying: Best Practices for Handling, Preparation, and Dehydration

Drying produce can be an attractive technique for adding value to your crop, reducing waste, and diversifying the products offered to consumers. The process of dehydrating produce extends shelf life by reducing water content and limiting the growth of microorganisms that can cause spoilage. Remain aware, though, that most dehydration processes are not kill steps — that is, they do not adequately kill foodborne illness-causing microorganisms. Some foodborne illness-causing organisms — for example, Salmonella — can survive in low-moisture environments for extended periods of time. Thus, safe food handling practices must be maintained throughout the produce drying process. This article discusses key steps you can take to avoid introducing foodborne pathogens during the produce handling and drying process.

Post-harvest produce handling

Sorting tables, storage bins, washing tubs and other post-harvest facilities can introduce contamination if pathogens are present on the surfaces or if post-harvest water is contaminated. Here are ways to prevent contamination during post-harvest handling:

For rinsing, washing, and cooling produce, use water with no detectable generic coli per 100 mL, or use water from a municipal water source (tap water).
Ensure that washing bins, sorting tables, and other food contact surfaces are cleaned and sanitized regularly to prevent growth of biofilms, a robust formation of microorganisms on surfaces that can be very difficult to remove.
- First, the surfaces should be cleaned to remove any organic matter (including dirt, leaves, and stems). This step ensures that the sanitizer works effectively.
- Second, the surfaces should be sanitized with a chemical that has been determined safe for food contact surfaces. This step helps kill vegetative microorganisms that can cause foodborne illness. Be sure to follow manufacturers’ instructions for appropriate use of the sanitizer.

Preparing produce

Some produce is cut, sliced, or ground into smaller pieces for drying. Any tools used to prepare produce should be cleaned and sanitized in between batches. Such tools may include, but are not limited to, cutting knives, cutting boards, and holding containers. Produce should be dehydrated immediately after it is prepared or immediately refrigerated to 40°F (4°C) or lower until you are ready to begin drying.

Slicing produce thinly ensures adequate dehydration. While each type of produce is different, we recommend cutting slices evenly to enable adequate and uniform drying throughout each piece of produce.

Here are some slicing preparation examples:

Apple slices should range from ⅛ to ½ inch
Brussels sprouts should be cut in half
Prunes should be pitted and cut in half
Blueberries can be dried whole

Pre-treatment

Pre-treatments can be applied to produce before the drying process begins. These treatments, which can be used as a coat or a soak, can consist of sulfur, acids, pectin, sugar, and/ or honey. Blanching is a pre-treatment in which the produce is immersed in boiling water or steamed briefly, without cooking it, and then immediately cooled by quickly submerging the produce in ice water. These pre-treatment processes not only improve the color and texture of certain commodities, but also can reduce the microbial load on the outside of the produce. However, a pre-treatment process that is not validated as a kill step may not necessarily eliminate microorganisms that are known to cause foodborne illnesses.

Here are some pre-treatment examples:

For fruits such as sliced apples or pears, soak in equal parts of lemon juice and water for 10 minutes immediately before dehydrating.
For most vegetables, blanch in a mixture of 1/4 teaspoon of citric acid per quart of water.

Drying process

Dehydrating at 140°F (60°C) or lower is recommended. Higher temperatures can cause a hardening effect on the outside of the produce, leading to inadequate internal dehydration and mold development over time.

Here is an apple drying process example:

Dry at 145°F (63°C) for one hour.
Reduce temperature to 135–140°F (57–60°C) for the rest of the drying time, allowing for approximately 6–12 hours of drying.
Test for doneness by pressing the dried apple slices between your thumb and pointer finger. The apple slice should be dry with no droplets of water forming under pressure.

Are you interested in learning more about commodity-specific produce drying processes?

Visit the Produce Drying Food Safety website: https://extension.purdue.edu/food-safety-for-produce-drying/index.html.

Click the “Food Safety Resources” tab to access a list of produce drying resources organized by commodity. If you have any additional questions, tap the “Ask an Expert” tab.