It’s a crucial step of any new product development journey: determining the shelf life of the product. Does the product last days, weeks, months, or years? And, most importantly, does it last as long as you need it to?
You want to make sure your consumer gets a safe product, but also one that tastes delicious and looks just how you meant it to be. You don’t want complaints about stale, rancid, or moldy products. Or, even worse, hear that people got sick of your product.
But, it can be tricky to determine shelf life, especially for a brand-new product. You don’t have the time, or budget, to wait months, or even years, or test for every single possible parameter.
Luckily, for most products, you don’t need years. Just focus on the one or two most important ‘failure mechanisms’. We’ll lay out the steps for you.
Step 0: How long should your shelf life be
It is best to think about the shelf life of your product from the get-go, as opposed to it being an afterthought. How long do you need?
If you’ve been running your business for a while, you probably have a decent idea of the time frame you’re looking. But, if you’re completely new, it can be challenging. Here’s a few things to keep in mind:
- If you’re not selling to consumers directly, your customers will need time to sell the product. They might want to keep some stock for weeks or even months, to prevent having to throw out unsold products.
- Your consumer will need enough time to use the product. Is it a portion they can eat in one go (think a single portion candy bar)? Or is it a product that will take days (think hummus) or weeks (think peanut butter) to finish?
- You’ll need time to transport your products. Are you selling locally, or nationally? In a small country (such as the Netherlands) or a big one (like the USA)? Fast, next-day delivery will be more expensive than slow, several-day delivery?
- This also brings in the next question, how expensive will your product be? That can impact the type of transport you can use.
- A shorter shelf life often results in more food waste than a longer shelf life. You simply have more time to sell your product. A fresh cob of corn spoils in a couple of days. A can of corn remains good for years. It’s a lot easier to plan for selling those cans than it is for selling the fresh cobs of corn.
Once you’ve got an initial idea of the shelf life you’re aiming for, it’s a matter of determining whether your product meet it. Though, of course, in an ideal case, you’d design your product such that it will get close to that shelf life.
Step 1: How does your product spoil?
Next up, it’s time to look at your actual product. The first question to figure out is to find out how the product spoils. Again, if you’ve made similar products before, you likely know how this works. If not, you will want to do some simple tests early on in development to get a grasp for what’s going on.
When looking at how products spoil consider the two main categories first:
- does a product become unsafe to eat AND/OR
- does it simply become less appetizing.
A product needs to be safe to eat
Of course, your product needs to be safe to eat when it leaves your premises. But, it should also remain safe to eat during its entire shelf life. One of the most important parameters to look at here is whether (pathogenic) microorganisms can grow in your product. If they can, you need to make sure they can’t grow to specified thresholds.
Whether microorganisms can grow depends on a lot of different factors:
- Storage temperature: does your product need to be stored in the fridge, freezer, or simply on the shelf? High temperatures result in faster growth of microorganisms and thus a shorter shelf life.
- Packaging conditions: how well does packaging protect your product from new microorganisms, but also, how does it prevent growth of pre-existing microorganisms (e.g. MAP slows down growth of certain microorganisms).
- Water activity (aw): when a product contains very little available water, microorganisms can no longer grow. More water enables the growth of a larger group of microorganisms.
- Acidity of your product (pH-value): most microorganisms can’t grow under very acidic conditions.
In some cases, such as a low enough water activity, or a low enough acidity, you will know quite sure on forehand that your product won’t spoil because of growth of microorganisms. Unfortunately, many products fall somewhere in between, and you will need to do some more in-depth analyses.
Keep in mind your local legislation
For certain product categories, such as fresh meat, cheeses, and babyfood governments all around the world have set criteria on food safety during shelf life. For instance, the growth of certain microorganisms may not extend above a certain value during shelf life. Or you may find requirements on the type of shelf life date you should use (e.g. a ‘use by’ vs. a ‘best by’ date).
A product needs to be nice to eat
Stale potato chips, rancid olive oil, yellow broccoli, bloomed chocolate, soggy crackers. They can all be perfectly safe to eat. However, still, most of us won’t buy or eat them anymore. In this case, your shelf life is not limited by the safety of your product, but by the quality of the product. Color, taste, texture, flavor, they’re all mostly quality defects.
This is great from a safety perspective, but, it can also be more challenging to determine shelf life for these products. When are potato chips too stale? When has olive oil turned too rancid? When are the crackers actually soggy? These are more subjective parameters. When you’re developing your product you will want to specify the ideal state, but also define from which point a product no longer meets the requirements.
Step 2: Design a shelf-life test
In step 1 you’ve determined what is the limiting factor for your product. Is it color, texture, growth of Salmonella, or growth of molds? Whichever the limiting factor is, that’s what you’ll be focusing on in the remainder of your research.
It is time to design a shelf life test.
These tests can be very simple. As an example, take a fresh salad with a shelf life of a couple of days. Wilting salad leaves are the limiting factor. Simply store a couple of salads under the actual storage conditions and note when you start to see wilting leaves. Ideally do this a few times, and you’ll have a good idea of the number of days you can store your product.
But, they can also be pretty complicated. Take a chocolate cookie with an expected shelf life of 12 months. The limiting factor is the loss of crunchiness of the cookie and blooming of the chocolate layer. You may need to store this cookie for months to see when exactly the cookies turn soft.
When designing these tests, here’s a few things to keep in mind.
1. Use actual storage conditions
When doing a shelf life test store the product as you would in real life. Use the actual packaging materials, temperature, humidity, etc. Don’t underestimate the importance of using the final packaging. That can make a huge difference.
In some cases you may want to add some additional scenarios. For instance, you might do tests at both 2°C (35°F) and 7°C (45°F) if testing a refrigerated product. Or, you may store a product at room temperature (20°C, 68°F) and 30°C (86°F) to imitate warmer days. If your product will be sold in a hot climate, you’ll need to adjust your temperatures.
2. Decide what to test for
If microbial spoilage is the limiting factor, you will need to analyze the amount of microorganisms on your product. If color is your limiting factor, ensure you have a way to measure color. That is, determine what you need to measure and how you’re going to measure it. You may need to use an external laboratory for these analyses. If you do, they’ll often be able to help you set up the work.
Some parameters are more subjective than others. Is the texture still good? Is the color still appealing? Sometimes you may be able to analyze these with a piece of equipment. However, in many cases you may need actual people to tell you what they think. You need a sensorial panel. These can be trained or untrained people who’d evaluate your products to determine whether it still meets your requirements or not.
3. Decide when to test
Lastly, you will want to determine when to test and how often to test your product. The more you test, the more expensive it becomes. For instance, if you expect your chicken to last for 7 days, you could test at just 6 and 7 days. If it passes those tests, you’re good to go. However, you could also decide to test at 5, 6, 7, 8 and 9 days. This will give you more information for how to chicken behaves during storage. Also, you might find that actually, you can store the chicken a little longer than you thought you could.
Scientists will like to test more as opposed to less. It helps to understand a product, and possibly also learn how to further improve the product. But, additional tests always come at a cost and don’t always actually give additional useful information.
How to accelerate shelf life tests
If products have a very long shelf life of months or even years it can be hard to design a decent shelf life study. In some cases, you can do an accelerated shelf life study. For instance, you can store the product at a slightly higher temperature to imitate a longer shelf life. Or, you can store it at a more disadvantageous humidity.
Whether this is possible depends on the product and the type of failure mechanism you’re looking for. For instance, you can’t store chocolate at high temperature, it will simply melt and not give representative data anymore. And you shouldn’t store icing sugar in a very humid environment or it will clump immediately, regardless of its shelf life.
Also, results of these accelerated 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.
Step 3: Evaluate and tweak
Once you’ve got your results in, it’s time to evaluate. Does your product meet the shelf life you were aiming for? If so, great, you’re done. If not, it’s time to take another look at your product again.
If the shelf life is too short, you will need to make some changes. Maybe you can use a packaging material that protects the product from oxygen? Or use a slightly different production process to lower the initial microbial load? Or, you may need to add a little more sugar to lower the water activity? Whatever it is, start tweaking as soon as you notice that you won’t make shelf life.
On the contrary, if your product stays good for a lot longer than you need it to, you might also want to make some changes. Could you use a cheaper, more sustainable packaging material? Could you leave out certain ingredients to make the product cheaper? Of course, you don’t have to change anything, but there might be ways to do things more efficiently.
Step 4: Launch and learn
Once you’ve met your target shelf life, your product is good to go. But, don’t stop learning. You will notice that your product is stored and treated differently than you expected. Maybe the supermarket stores it at lower temperatures. Or your customer might not have a sufficiently dry space to store the product. Keep an eye out and continue learning about your product.
Determining shelf life will become easier once you’ve already got some similar products in the market. If all you’re changing is the flavor of your product, you might not have to do a full blown study anymore. You’ll already know how it behaves. Use your past experience to continuously improve your shelf life study skills.
Determing shelf life is crucial for any (new) food product. If you’ve just developed a new product, you’ll also need to make sure your product can be stored safely and without losing quality. If not, your consumers might be disappointed and never return for another purchase.
But, determining shelf life can seem daunting and overly complicated. It’s why you want to design a smart and as simple as possible test.
Not sure what the shelf life of your new product should be? Reach out and we’ll discuss what options you might have.
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.