Accelerated shelf-life testing (ASLT): what it is, and what it is not

Nobody wants to wait a year to find out whether a product keeps for a year. Accelerated shelf-life testing (ASLT) is the industry’s way of getting an early read. It is a good tool, provided you understand what it measures and what it does not.

The idea

Expose the product to stress conditions that accelerate a defined deterioration mechanism: higher temperature, controlled relative humidity, more oxygen, light, or temperature cycling. Measure the relevant marker (water activity, peroxide value, texture, colour, taste) at fixed time points, and use a kinetic model to translate the rate under stress into the rate under normal storage.

The most common rule is Q10: by how much the reaction rate multiplies for a 10 °C rise. For lipid oxidation and many chemical reactions Q10 is between 2 and 4. In other words, storing at 40 °C instead of 20 °C can accelerate things 4 to 16 times. Behind it stands the Arrhenius equation, which links reaction rate to temperature.

When it works

• When the failure mechanism is known and mainly chemical: oxidation, colour change, vitamin loss, Maillard browning.
• When the product does not change phase at the stress temperature (a fat that melts at 40 °C is a different product).
• When there is a marker you can measure objectively, with a defined failure limit.
• When you have data from at least two or three temperatures, to calibrate the model rather than guess a Q10.

When it misleads

• The mechanism switches. At high temperature a product can fail from something that never happens under refrigeration: starch crystallizing differently, a protein breaking down. The result is a “failed” test on a mechanism irrelevant to the shelf.
• Moisture. Temperature acceleration does not simulate moisture uptake. For crisp products you need to control relative humidity, not only temperature.
• Microbiology. Microbial growth cannot be “accelerated” in a way that translates to shelf conditions. Here you are left with challenge tests and real-time testing.
• Packaging. Film barrier changes with temperature and humidity. What is measured at 40 °C does not always represent the barrier at 20 °C.

What you need before you start

1. A clear definition of the failure: the marker, and the value at which the product is unacceptable (fracture force below X newtons, or a taste score below Y).
2. A precise day-zero measurement, including aw, pH, moisture and texture.
3. Two or three temperatures (or humidities) and sampling intervals chosen in advance.
4. A real-time validation plan running in parallel, even if it takes longer.

How we do it

At Foodlab we start from a shelf-life simulation that shows which mechanisms are likely to dominate, and then choose the acceleration conditions for that mechanism rather than “40 °C because that is what people do”. Where the mechanism and the data allow, an Arrhenius model is translated into an estimate for normal storage. And always: accelerated testing complements real-time testing, it does not replace it.

More on the service at The Whole Package, and on the mechanisms themselves in Why does my snack go soft.