How to Safely Dehydrate Food: Temperature, Water Activity, and Jerky Rules

The home dehydration trend brought jerky-making to millions of kitchens, and most of it goes fine. But there’s a specific failure mode in meat dehydration that took a CDC outbreak to document properly. Once you understand it, the USDA’s two-step jerky recommendation makes immediate sense.

It comes down to the race between drying and killing.

What Water Activity Actually Is

Bacteria don’t need water in the way we might imagine. They don’t drown in it or evaporate without it. What they need is available water, which scientists measure as water activity (aw).

Fresh chicken sits at around 0.99 water activity. Most pathogenic bacteria require at least 0.91 to multiply. Drop below 0.85 and most bacterial growth stops. Drop below 0.60 and virtually no microbial activity is possible. That’s why properly dried foods are shelf-stable: you’ve removed enough water availability to stop microbial growth.

This is different from water content. Water activity measures how tightly water molecules are bound to food components. Sugar and salt bind water molecules, which is why heavily salted or sugared foods have lower water activity than their moisture content alone would suggest. A high-sugar jam can be 35% water by weight but still have a water activity below 0.85.

Properly dehydrated jerky reaches water activity around 0.70 to 0.75. Fruit leather reaches 0.60 to 0.70. These values are low enough to prevent pathogen growth during storage.

The problem is what happens during the drying process, before water activity gets there.

The Jerky Problem

In 1995, a multistate outbreak of Salmonella infections was traced to home-made jerky. Studies that followed, including research published by Nummer et al. in the Journal of Food Protection (2004), confirmed what the outbreak suggested: standard home dehydrators could leave viable pathogens in jerky.

Here’s the mechanism. Dehydrators typically operate at 130 to 140°F. That’s warm enough to dry the surface of meat relatively quickly. But as the outside surface dries and forms a crust, it becomes insulating. Heat transfer to the interior slows down. At the same time, the dry exterior creates an environment where bacteria on the inside can survive temperatures they wouldn’t survive in a moist environment.

This is the thermal resistance effect. Bacteria in dry conditions can survive higher temperatures than bacteria in moist conditions, because their cellular water content is lower and they’re less susceptible to heat damage.

The result: jerky made by placing raw, marinated meat strips directly in a dehydrator at 130-140°F may not kill all Salmonella or E. coli O157:H7, even if it looks properly dried and has appropriate water activity at the end.

The Two-Step Solution

The USDA FSIS recommends two acceptable methods for safe jerky.

The first is the pre-heat method: heat raw meat slices to 160°F (165°F for poultry) in a 275°F oven before placing them in the dehydrator. At this point, any surface pathogens are dead. The dehydration step then finishes moisture removal without a safety function to perform.

The second is the post-dehydration method: dehydrate first, then place finished jerky on a baking sheet in a 275°F oven for 10 minutes. This uses oven heat to reach the kill temperature after the jerky has dried to its final water activity. Studies confirm this method reaches sufficient internal temperatures to kill remaining pathogens.

Both methods work. The pre-heat method is somewhat easier to execute because you’re working with raw meat that’s easier to spread on a rack. The post-heat method lets you fine-tune the dehydrator time for texture and finish in the oven.

What doesn’t work: relying on longer dehydrator time alone to solve the problem. More time at 130-140°F in a standard dehydrator doesn’t reliably reach the kill temperature inside the meat.

Fruit and Vegetables Are a Different Problem

The jerky concern is specific to raw meat. Fruits and vegetables have a different safety profile because:

They don’t typically carry the same pathogen load as raw meat, especially not E. coli O157:H7 and Salmonella at the concentrations found in meat.

Their primary safety concern is surface contamination, which lower temperatures handle reasonably well.

Their water activity drops faster relative to pathogen kill requirements.

Standard dehydrator temperatures are appropriate for fruit and vegetable dehydration. The main safety practices are washing produce thoroughly before dehydrating and making sure finished products reach the right texture (brittle for vegetables, leathery without moisture pockets for fruit).

Commercial vs Home Dehydration

Commercial jerky manufacturers use validated processes. They measure water activity with calibrated meters and test finished products. Many use higher-temperature dehydrators than home units or separate heating tunnels that guarantee the kill step. Some use humidity-controlled chambers that can run at 160°F without over-drying the surface before the interior reaches temperature.

Home dehydrators don’t have these controls. Most don’t have validated temperature accuracy either. A dehydrator labeled 140°F may run 5 to 10 degrees cooler in cold spots. That’s why the two-step method matters: it takes the kill step out of the dehydrator’s hands entirely and gives it to the oven, where temperature control is more reliable.

Storage After Dehydration

Properly dehydrated food at water activity below 0.85 won’t support bacterial growth, but it can still go stale, oxidize, or absorb moisture from the environment. Store dehydrated foods in airtight containers, ideally with oxygen absorbers for long-term storage. Keep away from light and heat, which accelerate fat oxidation.

Vacuum sealing extends shelf life significantly for dehydrated meat. Commercially dried jerky in sealed packaging typically lasts 1 to 2 years. Home-made jerky stored in airtight containers at room temperature is best consumed within 1 to 2 months. Refrigeration or freezing extends this to 3 to 6 months (refrigerator) or up to a year (freezer).

If dehydrated food ever feels sticky, shows any moisture, or smells off, discard it. Those are signs the water activity crept back up.