How Does a Dehydrator Kill Bacteria Present in the Food?

Last Updated on October 2, 2023

Dehydration is an effective way of killing bacteria, viruses, and mold. By removing the water from food, you effectively remove the working environment that these pathogens need in order to survive.

Does a dehydrator kill bacteria? A dehydrator is primarily designed to remove moisture from food, which inhibits bacterial growth. While the dehydration process can reduce the number of bacteria in food, it doesn’t necessarily eliminate all pathogens. To ensure bacteria is effectively killed, it’s essential to preheat the food to a safe temperature before dehydrating.

Dehydration also inhibits the growth of new bacteria, so even if there are a few surviving cells, they will not be able to reproduce and cause illness.

Dehydration is a gentle way to preserve food, and it does not require the use of chemicals or high temperatures. As a result, it is considered a very safe method of preservation.

What is Dehydration and the Influence of Dehydration on Food Preservation?

The principle of dehydration as a method of food preservation is simple – water activity (aw) in food must be reduced to a level where microbial growth and activity are inhibited. Water activity can be decreased by either removing water from the food product or by adding sugar or salt, which will bind the water molecules and make them unavailable for microbial metabolism.

Dehydration is a process that uses low temperatures and low humidity to remove water from food. The water is removed through evaporation, leaving the food in a semi-dry state.

Dehydration is an effective method of food preservation because it:

• Reduces the water activity (aw) in food
• Inhibits the growth of microorganisms
• Minimizes oxidation
• Inactivate enzymes
• Maintain or improve the flavor, texture, and color of the food

Thus, dehydration is regarded as a very safe method of preserving food.

Dehydration can be used to preserve both perishable and non-perishable foods.

To kill bacteria and other microorganisms, perishable foods such as fruits, vegetables, and meat must be dehydrated rapidly. Non-perishable foods such as grains, nuts, and seeds can be dehydrated at a slower rate.

The dehydration process can be done using a dehydrator, an oven, solar or the sun.

• A dehydrator evaporates water by circulating hot air over food.
• Ovens can also be used for dehydration, but they must be set at a low temperature (140°F/60°C or below) to prevent the food from cooking.
• Solar dehydrators use the heat of the sun to remove water from food.
• Food can also be dried outdoors in the sun, but it must be covered to protect it from insects and dirt.

How Does a Dehydrator Kill Bacteria?

Dehydration is a powerful bactericide that kills bacteria in three ways: removal of water, high temperatures, and low humidity.

By Removing the Water

This process works by removing water and moisture content from the cells of the bacteria or pathogen, causing them to shrink and eventually die. A dehydrator evaporates water by circulating hot air over food.

As the water is removed, the bacteria cells are also dried out, eventually dying.

Exposure to Heat

Bacteria were killed by the dehydrator’s heat, which was too high for them to survive. 

Bacteria lose the wet environment they need to thrive and multiply. And when exposed to high temperatures, bacteria are quickly killed off.

With Low Humidity

The low humidity in a dehydrator also inhibits the growth of bacteria. The lack of water in the air prevents the bacteria from absorbing moisture, and without moisture, the bacteria cannot grow or reproduce. Even if a few cells survive, they cannot reproduce and cause illness.

As a result, dehydrated foods are safe to eat without fear of foodborne illness. So if you’re looking for a simple and effective way to preserve your food, consider dehydrating it.

Factors That Impact the Bactericidal Efficacy of Dehydration

The Type of Food Being Dehydrated

The type of food being dehydrated can impact the efficacy of the process. For example, foods with high fat content are more resistant to the bactericidal effect of dehydration than leaner foods.

This is due to the fact that fat acts as a barrier, protecting bacteria from the drying process. As such, lean meats and poultry are more susceptible to bacterial growth during storage than fatty meats and poultry.

On the other hand, fruits and vegetables differ in their susceptibility to bacterial growth during storage. This is because fruits and vegetables have a higher water content than meat or grains.

So, in general, fruits with a high water content are more susceptible than those with low water content. Therefore, it is important to take into account how the food is dehydrated when considering its storage life.

The Water Activity or AW index

Water activity (aw) is a key factor in the safety of dehydrated foods. Basically, water activity is a measure of the amount of water available for microbial growth.

The water activity (aw) measures the amount of free water in a food. The higher the AW, the more free water there is in the food.

Free water is the water that is available for microbial growth. The USDA recommends that dehydrated foods have a water activity of 0.85 or less to prevent the growth of bacteria, mold, and yeast.

To meet this water activity goal, food must be dried to a moisture content below 10%, which is the point at which water activity is 0.85 or less.

By reducing food’s water activity, molds and bacteria can’t grow, germinate, or produce toxic compounds. As water activity decreases, microorganisms go through a lag phase and grow slower.

So, food can be made safe to store by lowering water activity. Microorganisms are classified into different groups according to their water activity (aw) requirements for growth.

For example,

• Staphylococcus aureus is a gram-positive bacterium that requires an aw of 0.86 for growth.
• Halophilic bacteria are those that grow best in high salt concentrations and have a minimum AW requirement of 0.75.
• In general, gram-negative bacteria have a higher minimum AW requirement than gram-positive bacteria. This is because gram-negative bacteria have a lipopolysaccharide layer in their cell walls, making them more resistant to desiccation.

By understanding the water activity requirements of different microorganisms, food manufacturers are able to control the AW of their products and prevent the growth of spoilage bacteria.

Dehydration Temperature

Dehydrators typically have a temperature range of 95-160 degrees Fahrenheit, and the recommended temperature for dehydrating foods is 140 degrees Fahrenheit or below.

At this temperature, enzymes are inactivated, bacteria are killed, and the food is dried quickly enough to prevent the growth of mold and yeast.

Humidity

The air in a dehydrator is also very dry, with a relative humidity of 10-20%. This low humidity further prevents microorganisms’ growth and helps preserve the food. The drier the air, the more effective the dehydration process will be in terms of killing bacteria.

Storage Temperature

Another factor that impacts the safety of dehydrated foods is the storage temperature. The USDA recommends that dehydrated foods be stored at a temperature of 10°C (50°F) or below to prevent bacterial growth. 

Proper Packaging

Dehydrated foods must be properly packaged to prevent the re-absorption of moisture from the air. Moisture can cause the growth of bacteria and mold, and it can also cause food to spoil.

The best way to package dehydrated foods is in vacuum-sealed bags or canning jars. If you are using canning jars, be sure to seal them with a new lid and screw ring.

If you are using vacuum-sealed bags, be sure to use a food saver or similar device to remove all the air from the bag.

You can also package dehydrated foods in plastic bags, but be sure to remove as much air from the bag as possible. You can do this by squeezing the air out of the bag or using a vacuum sealer.

Once dehydrated foods are packaged, they should be stored in a cool, dark place. A cupboard or pantry is typically ideal.

Dehydrated foods can also be stored in the refrigerator or freezer, but they should be brought to room temperature before eating to prevent spoilage.

Shelf Life

Dehydrated foods have a much longer shelf life than fresh foods. When stored properly, dehydrated foods can last for months or even years.

The shelf life of dehydrated foods depends on several factors, including the type of food, the moisture content of the food, the storage temperature, and the packaging.

Dried meats generally have the shortest shelf life (1-2 months), while dehydrated fruits and vegetables can last for 6-12 months.

Size, Shape, and Arrangement of Food

The size, shape, and arrangement of food items in the dehydrator are important factors to consider when dehydrating foods. The goal is to have as much surface area exposed to the air as possible so that the food can dry evenly and quickly.

If food items are too close together, they will block the flow of air, and the food will not dry properly. Likewise, if the food items are too small or thinly sliced, they will dry out too quickly and become burnt.

To ensure even drying, it is best to dehydrate food items that are similar in size and shape. Do not stack food items on top of each other, and make sure there is at least a 1-inch space between each food item.

If you are dehydrating a large quantity of food, you may need to dehydrate in batches to ensure proper airflow and even drying.

How to Test If Dehydrated Foods Are Dry Enough?

One of the most important things to remember when dehydrating foods is that they must be dried completely to prevent spoilage. If there is any moisture left in the food, bacteria, and mold can grow and cause the food to spoil.

The best way to test if a food item is sufficiently dehydrated is to do the pinch test.

To do the pinch test, simply take a small piece of the food between your thumb and forefinger and squeeze it. If the food feels leathery or pliable, it is ready. If the food feels moist or sticky, it needs to be dried for longer.

Also, a perfectly dehydrated product should snap when you bend it. The food has shrunk in size but should not have changed in shape.

Another way to determine how dry, dehydrated foods are is to use a moisture meter. These devices measure the water content of food and can give you a good idea of how well the dehydration process has gone.

Try storing the food in an airtight container and checking it after a day or two. If there’s any condensation on the inside of the container, the food isn’t dry enough and needs to be dried for longer.

What are the Signs of Spoilage in Dehydrated Foods?

Several signs can indicate that dehydrated food has gone bad. These signs include:

• The food has changed color or developed dark spots
• The food has a sour smell
• The food is sticky or moist
• The food has mold growing on it
• Presence of small insects
• Liquid seeping from the food

If you see any of these signs, it is best to discard the food as it may no longer be safe to eat.

Special Tips and Safety Precautions

Preventing bacteria and mold growth when dehydrating foods requires a few precautions:

Keep everything clean: Use clean, fresh produce that has been washed and dried. Moldy or spoiled food should not be dehydrated. Wash your hands thoroughly before handling any food. Use clean cutting boards, knives, and other utensils. Do not cross-contaminate using the same raw meat and fresh produce utensils.

Small pieces: Cut food items into uniform pieces that are no more than 1/2 inch thick. Do not overcrowd the dehydrator. Arrange food items in a single layer on the dehydrator trays.

Time: For maximum efficiency, it is recommended to use a dehydrator with a timer so that you can ensure that the food is exposed to the dehydrating conditions for the optimal amount of time.

Never dehydrate raw meat: Raw meat and poultry should not be dehydrated. These foods must be cooked before they are dried. Raw meat is typically infected with harmful microorganisms, but dehydrators and oven dehydration can’t destroy them.

Heat the jerky to 160°F (71°C) before dehydrating it. To make jerky safe, heat it to 160°F for beef and 165°F for turkey or chicken jerky before dehydrating.

Don’t use oil: Garlic and onions should not be dehydrated in oil. The oil can become rancid during the drying process.

Store separately: Do not store dehydrated foods in the same container as fresh or cooked foods. Store dehydrated foods in an airtight container in a cool, dark place. Dehydrated foods are best used within 6 months.

Be cautious: If you are unsure whether a food item has been properly dehydrated, it is best to err on the side of caution and throw it out. Do not consume food that you are not confident is completely dry.

Blanch before dehydrating: If you are concerned about bacteria, it is advisable to blanch foods before dehydrating them. Blanching will kill most bacteria on the surface of the food.

While dehydration did kill most of the bacteria, a small amount survived by going into hibernation mode deep within the cells of the food. These bacteria can come out of dormancy and multiply when rehydrated, potentially causing food poisoning.

To blanch food items, simply submerge them in boiling water for a few minutes before dehydrating. The process should kill most bacteria on the food’s surface.

Try Your Hand at Dehydration for Healthy Preservation

Now you know all about the bactericidal efficacy of dehydration, as well as some tips and tricks for safe dehydrating practices. Why not give it a try?

It’s time to put this cool technique to the test; let’s explore the wonders of dehydration. You will be happy with how much more flavorful your food tastes after trying this new skill!