Research at Campden BRI suggests that food should be delivered within 24 hours to ensure it remains chilled during non-chilled delivery.

The study investigated the impact of external temperature on ready meals prepared for courier to understand how the temperature would change during transit. The results will help food businesses keep their products chilled when out for delivery so that they are safe for the consumer.

The research comes as the total number of food delivery users in the UK rose to 22.5 million earlier this year – a 9.8% increase compared to the same period in 2019, according to Statista.

Campden BRI microbiologist Linda Everis, who led the study, said: “We’ve seen an explosion in food delivery this year. Meal-kit companies are growing ever popular while some supermarket retailers have teamed up with takeaway courier groups to meet demand. But with this rapid rise come concerns over food safety. We conducted this study to answer the question of how long food should be out for delivery until it exceeds 8°C.”

“Overall, this research highlights that certain factors…all play an important part in determining whether food remains chilled. For this reason, food businesses should undertake studies like this one before embarking on this type of delivery service.”

For products sold in the UK, 8°C is the maximum temperature that chilled products can be legally stored. Exceeding this temperature could make foods unsafe and susceptible to spoilage, impairing the quality of the delivered foods.

Food delivered via non-chilled courier is potentially vulnerable to fluctuations in temperature that occur throughout the day and night, according to Campden BRI. The study reflected these conditions, with chilled and frozen ready meals being packed into a cardboard box with ice packs and bubble wrap, and then stored at various temperatures.

The research showed that the rate at which a product reaches 8°C can depend heavily on the type of product it is and, sometimes, its placement within a box. For example, two salt and pepper chicken ready meals at the bottom of a box exceeded 8°C within 40 hours whereas the adjacent egg fried rice only peaked at around 5°C. This variation was also seen for products at different levels within the same box.

The external temperature played a pivotal role in determining how quickly the ready meals increased in temperature. For example, at an external temperature of 20°C, one of the salt and pepper chicken ready meals climbed 8°C from 0°C within nine hours, putting it directly on the cusp of exceeding the UK legal maximum storage temperature.

According to the study’s findings, there is potential to pack products strategically to help them remain under 8°C. For example, the researchers found that some chilled ready meals took longer to rise in temperature when placed between two frozen ones – a tactic that could be applied if a long delivery time is expected. However, an independent study would be required to ensure the chilled products were not freezing.

Craig Leadley, the head of strategic knowledge development at Campden BRI who oversees the research programme, said: “Overall, this research highlights that certain factors including the type of product, its placement in a box, how it’s packed, the time of day it’s in transit and how long it will take to reach the consumer all play an important part in determining whether food remains chilled. For this reason, food businesses should undertake studies like this one before embarking on this type of delivery service.”

Photograph: Campden BRI microbiologist Linda Everis.