Heritage Field Notes · Category G
Sun drying and air drying preserved food across every civilization before electric dehydrators existed. The USDA documented American household drying methods in 1938. The physics hasn't changed.
In 1938, the USDA Bureau of Home Economics published "Drying Vegetables, Fruits, and Herbs at Home," a comprehensive guide to food dehydration without electric equipment. The timing was the late Depression — households were looking for preservation methods that required minimal cash outlay. Drying qualified: the only required inputs were the food itself, a screen or rack for spreading, and suitable weather or a low-temperature oven.
The bulletin addressed three drying methods: sun drying (outdoor drying in direct sunlight), shade drying (outdoor drying in moving air, out of direct sun), and oven drying (indoor drying at the lowest oven temperature). Each method suited different foods and different climates. The common thread was the underlying mechanism: removing moisture to below the threshold (around 10-15% for most foods) where microbial activity cannot proceed.
Modern electric dehydrators replicate these conditions with better control — consistent temperature, built-in airflow, precise timing. But the original methods work. Households without dehydrators, households facing power outages, and households in hot dry climates where sun drying is practical can produce high-quality dried food using the methods the bulletin documented.
Primary Source
Drying Vegetables, Fruits, and Herbs at Home
U.S. Department of Agriculture, Bureau of Home Economics. Miscellaneous Publication No. 339. Washington, D.C.: Government Printing Office, 1938.
Public domain — U.S. government work. Search the Internet Archive →
Three Methods
Best for: fruits (grapes, apricots, figs, tomatoes), hot dry climates, 3-5 consecutive days of sun forecast. Requires: screens or trays, covering at night and during dew, protection from insects and birds.
The bulletin specified a minimum temperature of 85°F and relative humidity below 60% for successful sun drying. These conditions exist reliably in the Southwest, Mediterranean climates, and hot dry summer weather elsewhere. Humid climates — the Southeast, Pacific Northwest — are poorly suited to sun drying.
Best for: herbs, flowers, some vegetables. Preserved color and volatile compounds better than sun drying. Requires: good air circulation, protection from moisture. This is the same method documented in the herb drying bulletin.
The bulletin noted that some foods — particularly green vegetables — lost their color in direct sun. Shade drying under cover with good airflow preserved green color while still removing moisture adequately.
Best for: vegetables, all climates, rainy weather, when faster results are needed. Requires: an oven that holds 140-160°F, racks or trays, time (4-12 hours depending on food). Leave the oven door slightly open for airflow.
The bulletin specified 140°F as the optimal oven drying temperature — hot enough to drive moisture out efficiently, low enough to avoid cooking the food. Many modern ovens don't go this low; using the lowest setting with the door ajar approximates the condition. A thermometer is useful.
What Dries Well
The bulletin organized produce by pre-treatment requirements and drying method. Most vegetables required blanching first; most fruits required sulfuring or acid treatment to preserve color and vitamin content.
Blanching (brief boiling, then ice water) stops enzyme activity that causes off-flavors and color loss during drying. The bulletin documented it as required for most vegetables; fruits generally require no blanching.
The bulletin documented sulfuring (burning sulfur and exposing fruit to the fumes) as the superior color-preservation method. Lemon juice or ascorbic acid dip is the modern safe substitute — adequate for home use, produces slightly darker results.
What It Teaches
Drying is the preservation method with the longest track record — it predates fermentation as a documented human practice and has been used on every inhabited continent. What made it universal was its simplicity: heat and airflow. No salt required. No special containers. No chemicals. No electricity.
The modern electric dehydrator makes drying easier and more consistent. But the 1938 bulletin's methods work in its absence. An oven that holds 140°F produces the same result as a dehydrator at the same temperature, at the cost of somewhat higher electricity use and less even airflow. Sun drying in appropriate climates produces results equivalent to commercial dried fruit. Screen racks built from common materials serve the purpose adequately.
The most resilience-relevant application is the summer and fall harvest window. A vegetable or fruit garden produces in abundance during a short season and nothing the rest of the year. Drying converts the summer surplus into shelf-stable food that spans the gap. The 1938 bulletin was documenting exactly this practice — not emergency preparation, but seasonal food management as a household discipline.
For preparedness specifically, a household that knows how to dehydrate food without electric equipment has a preservation option that functions when power is out, when dehydrators break, or in any scenario where grid-dependent methods fail. The skill requires practice in good conditions; acquiring it during a disruption is harder than having it already.
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