Learn the science behind:
How long do muffins remain fresh? When does sausage start to spoil? How long can you store that cheese for?
As a consumer, you’d use the dates on the product, and your common sense to determine whether something is still good. However, as a manufacturer, you have to know your product well enough to be able to make those calls.
If you’re scaling up your food production, it’s one of the crucial parameters to figure out: how long can your product be stored for? For some products it’s easy, for others it can be very complex. How you pack and store the product impact shelf life. But so do its composition, the process its undergone, and local legislation.
- Shelf life = quality + safety
- How to determine a product's shelf life
- Determine how your product will spoil
- How to design a shelf life test
- Use your experience
Shelf life = quality + safety
For most* food products you will need to know how long the product can be stored for, under the conditions given. The period of time that you can store the product for is called the shelf life. This is crucial for your customers since they’ll then know when the product is still good to consume.
The shelf life of a product is determined by two factors:
- Food Safety: is there a time period within which the product will be unsafe to eat? For example, due to growth of bacteria?
- Food Quality: when has the quality of the product deteriorated too much. In other words, its flavor, color, etc. might have changed and become unappealing, but it might still be perfectly safe to eat.
Shelf life legislation
Legislation around determining and setting the shelf life for food products varies around the world. Terminologies differ, requirements differ, and so in this article, we will not focus on any legal requirements around shelf life.
That said, it is wise to look up your local applicable legislation for your product since in some cases the maximum shelf life of your product category is already given.
As a producer, you’re almost always responsible for determining the shelf life of your product.
As an example, in Europe, regulation no. 1169/2011 states which products need to contain a ‘use by’ date.
How to determine a product’s shelf life
When determining the shelf life of a product there are several steps and considerations that you should take into account.
Determine how your product will spoil
Whenever you’re trying to determine the shelf life of a product, you need to know how the product will spoil. If you don’t, it will be hard to design appropriate tests. For instance, if you know a loss of color will be an issue, you’ll have to make sure to monitor that. On the other hand, if you know certain bacteria might make the food unsafe, you’ll need to monitor those.
Ask yourself the following questions:
Can microorganisms grow in your product?
Whether or not microorganisms can grow in a product depends on the composition of that product. Important factors to know are:
- Water activity (aw): a measure for the amount of available water in a product. The higher the water activity, the more likely it is microorganisms can grow on/in the product.
- pH-value: a measure for the acidity of a product. Under a certain pH value most microorganisms can no longer grow, or only those that don’t make you sick.
- Temperature: most microorganisms grow more slowly at low temperatures, or stop growing completely in a freezer at -18°C (0°F).
- Packaging material: the gases surrounding your product will impact whether or not microorganisms can grow. For example, vacuum packaging does not contain any air. The lack of oxygen prohibits the growth of certain microorganisms. Modified gas atmospheres can also slow down or eliminate growth.
A lot of information is available online and in books about these factors. Also, in a lot of countries, those products most susceptible to the growth of harmful microorganisms are tightly regulated. As such, regulations will tell you what to do in quite some detail. This is often the case for meat products for instance.
How does the sensory quality change?
The sensory quality of a food describes how you experience eating a food. It’s about the color, taste, texture, flavors, etc. It is important to note that these changes do not make a product unsafe to eat. It’s merely less appealing.
How does this change over time for your product? For instance, chips can become soggy if not stored well, and certain products such as broccoli may lose their color.
Sensory quality is a more subjective parameter than the growth of microorganisms. To determine it, you might need to set up panels of taste testers or appoint experts in your company who can make the call whether a product is still good or not.
Which is the limiting factor?
Once you’ve gathered data on these two parameters, it’s time to find out which of the two is the limiting factor. Which is the one that doesn’t meet your minimum criteria fastest?
Once you know this, you can start to design your shelf life tests.
How to design a shelf life test
Decide on your parameters
If microbial spoilage is the limiting factor you will need to set up a microbiological piece of research. At regular time intervals you will need to check how many microorganisms are present on your product. This will likely need to be done at an (external) microbiological laboratory.
How often you need to test strongly depends on the expected shelf life, the type of product, the storage conditions, and generally speaking the risks involved.
If sensorial spoilage is your limiting factor, tests tend to be a little less complicated. You can test the product by looking at it, tasting it, etc. Design a simple, but effective grading system for the parameters that are important.
Use representative storage conditions
When doing a shelf life test it is important to use those conditions under which the product will be stored for in real life. Choosing the correct temperature is especially important.
Try using a ‘worst case’ scenario. So if your product should be stored in the fridge, don’t assume it’s stored at 2°C (35°F). Instead, assume it’s stored at 7°C (45°F).
Keep in mind that a few degrees difference can make a huge impact on shelf life. For some products with a shelf life of several days, the difference can easily be a few days.
Use the final packaging
During the development of your product, you may have just stored your product in whichever materials you had available. However, the packaging material can have a huge impact on the shelf life of your product. So, when designing a test, make sure you use the final actual packaging.
How to accelerate shelf life tests
Some products have a very long shelf life, months, or even years. It might be hard to design a good shelf life study for these products. In some cases, you may be able to accelerate the shelf life by storing the product at a higher temperature. However, this is not always possible. If a product would melt, for instance, it will no longer give a representative result.
Also, the results aren’t always representative. At higher than normal temperatures your product might spoil in a different way than it normally would. Doing the test under real actual conditions will almost always give the best results.
Use your experience
The good thing about shelf life determination, is that you can truly build up your expertise. Once you’ve done the process a few times for your products, you’ll get a better sense for what impacts the shelf life and which are your most important limiting factors.
Disclaimer: This article is written for informational purposes only and is no official advice regarding legislation and food safety. Always consult a (local) expert for advice where appropriate.