How to Measure Water Activity in Beef Jerky
Beef jerky has become a staple product in the American diet.
According to research done by the Simmons National Customer Survey (NHCS) in 2019 and the U.S. Census, approximately 50% of the U.S. population, which is nearly 160 million people, eat meat snacks and beef jerky regularly.
This is mainly due to the taste, texture, convenience, and long shelf life of beef jerky.
One way to ensure your beef jerky is high-quality (taste, texture, long shelf life) and safe is by understanding and achieving the right water activity level.
We explain more below.
Defining Beef Jerky
Before we dive into water activity, it’s important to understand what can be labeled as beef jerky.
According to the USDA, to label a product as “jerky” it must have a moisture:protein ratio (MPR) of 0.75:1 or less.
Here are some other labeling requirements:
- Beef Jerky – produced from a single piece of beef
- Beef Jerky Chunked and Formed – produced from chunks which are molded and formed and cut into strips
- Beef Jerky Ground and Formed or Chopped and Formed – produced as described, molded and formed and cut into strips
To see all labeling requirements, refer to the USDA Food Standards and Labeling Policy Book.
Some manufacturers rely upon the MPR for determining whether their process adequately dries the jerky to produce a shelf-stable product. However, MPR is an inappropriate indicator of shelf stability.
Understanding the Basics of Water Activity in Beef Jerky
Water activity (aw) refers to the amount of unbound water molecules in a food product and is measured on a scale of 0 to 1.
- Water activity of 0 = food is completely dry
- Water activity of 1 = pure water
- Water activity of 0.99 = raw meat
The USDA requires the following water activity levels for beef jerky:
- Aerobic conditions = aW of 0.85 or less
- Anaerobic condition = aW of 0.91 or less
Many processors may dry the product down to 0.83 to be on the safe side.
This is because microorganisms such as bacteria and fungi require a minimum water activity level to grow and cause spoilage. A low water activity level in beef jerky helps to inhibit the growth of these harmful microorganisms, making it a safer and longer-lasting food product.
What Factors Affect the Water Activity Level in Beef Jerky?
There are three factors that either increase or decrease the water activity level in your beef jerky. Understanding these factors will help ensure your water activity level is in line with USDA requirements.
The temperature at which the beef jerky is dried can have a significant impact on its water activity level.
- Too high = the beef jerky can become too dry and brittle, which can affect its texture and flavor.
- Too low = the beef jerky may not dry completely, which can lead to a higher water activity level and an increased risk of microbial growth.
Salt is a natural preservative that helps to inhibit the growth of bacteria and other microorganisms. When salt is added to beef jerky, it binds to the water molecules, which limits the amount of unbound water available for microbial growth.
Beef jerky with a higher salt content typically has a lower water activity level, which helps to extend its shelf life.
Finally, the other ingredients that are added to beef jerky can also affect its water activity level.
- Sugar and other sweeteners can impact the water activity level of beef jerky.
- Vinegar and other acidic ingredients can lower the water activity level.
The type of spices and seasonings used can also have an impact on the water activity level, as some ingredients may contain moisture or affect the pH level of the beef jerky.
Why is Measuring Water Activity in Beef Jerky Important?
Water activity level is closely tied to food safety and product quality. Zeroing in on the right water activity level can greatly improve your beef jerky.
Ensuring Food Safety
Water activity is directly related to the growth of microorganisms such as bacteria and mold.
If the water activity level in beef jerky is too high, it can create an environment where harmful microorganisms can thrive, potentially causing foodborne illnesses.
By measuring water activity, manufacturers can ensure that the water activity level in their beef jerky is below the threshold that supports the growth of harmful microorganisms. This helps to ensure the safety of the product and reduces the risk of foodborne illnesses.
The water activity level of beef jerky can also affect its texture and flavor.
- Too low = beef jerky can become tough and difficult to chew.
- Too high = beef jerky can become soft and lose its characteristic texture.
Extending Shelf Life
Water activity is an appropriate indicator to verify if jerky is properly dried for food safety.
Minimizing available water (e.g., achieving a sufficiently low water activity) is necessary to achieve shelf stability, provided measures are taken to address mold growth.
As we mentioned at the beginning of this article, in order to achieve a shelf-stable product, water activity should be at:
- 0.85 or lower for products stored in an aerobic or oxygen-containing environment
- 0.91 or lower for products vacuum packaged in an oxygen-impervious packaging
Measuring water activity ensures that the product is within those critical limits and has achieved shelf-stable conditions.
Optimizing Production Processes
By understanding the water activity level at different stages of the production process, manufacturers can make adjustments to ensure that the final product has the desired water activity level.
For example, if the water activity level is too high during the drying process, manufacturers can adjust the temperature or humidity levels to achieve the desired water activity level.
How to Use a Water Activity Meter to Measure Water Activity
A water activity meter is a device that is used to measure the amount of water present in a sample and should be used in every beef jerky production plant.
We teach participants of our Marination and Thermal Processing Short Course how to use one after cooking their beef jerky.
Using one is pretty simple.
First, you need to prepare a sample of the beef jerky that you want to test. This sample should be small enough to fit into the water activity meter.
Next, you need to place the sample into the water activity meter and wait for the reading to stabilize. The water activity meter will measure the amount of water vapor present in the air surrounding the sample. This reading can then be converted into the water activity level.
It is important to note that using a water activity meter is not the only way to determine the ideal moisture content in beef jerky. Other methods, such as visual inspection and taste testing, can also be used. However, using a water activity meter is a more accurate and reliable method.
Finding the Ideal Water Activity Level
Once you have determined the water activity level of the beef jerky, you can use this information to calculate the ideal moisture content.
The ideal moisture content will depend on the water activity level, the type of beef jerky, and the desired texture of the final product.
We recommend working with a meat scientist to help determine the water activity level that is best suited for your beef jerky.
You will save time and money trying to figure it out on your own and get valuable insights into what makes for quality beef jerky.
Our team of meat scientists is able to set up testing in our Innovation Center to find the right recipe and water activity level for your beef jerky.