Shelf Life and Packaging

Shelf life is more than just an expiration or best by date. Shelf life relates to how long a product complies with food guidelines and stays desirable, which can be affected by sensory characteristics and chemical, physical, and microbial properties. Predicting shelf life is essential to the success and safety of a product. Read on to troubleshoot common shelf life and packaging issues. 

What Ends Shelf Life?

Many factors can lead to the end of shelf life, including microbial growth, chemical changes due to oxidation, physical deterioration such as caking and clumping, other textural changes, vitamin degradation, changes in color, and other enzymatic reactions. The good news is that these can be predicted and even prevented by understanding the effect of water activity on the product, conducting accelerated shelf-life testing, choosing proper packaging, and understanding how adding ingredients will affect the product. 

Water Activity

Each product has a critical water activity level (known as the RHS) when undesirable changes that affect shelf life begin. The relationship between water activity and moisture content is represented by the moisture sorption isotherm, which can show you exactly which moisture level changes will occur in your product. It is also important to remember that the RHS of each product is temperature-dependent. As the temperature of the product increases, the critical water activity level goes down. This relationship is essential to understand since the product is most stable below the RHc. 

Accelerated Shelf-Life Testing

Accelerated shelf-life testing aims to gather empirical data about product failure due to temperature-dependent RHc. Although it is sometimes tempting to use shelf-life data from similar products, the best practice is to obtain precise shelf-life data for each specific product. Accelerated shelf-life tests can be completed by selecting three water activity levels and three temperatures and testing the product at a combination of these values. Then, as you track the progress of the mode of failure you are assessing, you can determine at which values shelf life are compromised. 

Packaging

It’s no surprise that shelf life and packaging go hand-in-hand. To fully understand how your packaging will affect the water activity level of your product, you need the water vapor transmission rate (WVTR) of the packaging, the testing conditions, the surface area of the packaging, and the mass of the product in the package. You will also need information about the packaged product's storage conditions, including the temperature, humidity, atmospheric pressure, and of course, the critical water activity level or RHc. Armed with this information, and through the correct shelf life calculations, you can identify which type of packaging properties and materials will extend the shelf life of your product. 

Additional Ingredients

Shelf life also needs to be reassessed when additional ingredients are added to a product. Creating a moisture sorption isotherm for each ingredient of a recipe will allow you to calculate the final water activity of the mixture or recipe without making and testing the final product. The same is true for adding additional ingredients, such as seasoning, to a product. By knowing the RHS of each product, you can calculate the final product's RHc and water activity level. 

In a Nutshell

Breaking it down into seven easy-to-follow steps, here’s a final overview of best practices when troubleshooting shelf life and packaging issues. 

• Identify the modes of failure that end shelf life

• Pinpoint critical water activity levels

• Perform accelerated shelf-life tests

• Determine desired shelf life

• Calculate proper packaging

• Reassess after formulation changes

• Prove shelf life predictions with empirical data

For specific examples of accelerated testing and walk-throughs of the calculations used to determine packaging and the final water activity when adding ingredients to a product, please watch the entire webinar above.