Bread alert: chemical engineers reveal worst sandwiches for the climate

DO you want to do your bit for the climate at lunchtime? If so, chemical engineers say you should avoid ready-made sandwiches and go green by making your own.

A new study analysing the carbon footprint of the 11.5bn sandwiches eaten in the UK each year has found that the average impact from homemade sandwiches is around two-times lower than the ready-made equivalent.

The team from University of Manchester looked at the lifecycles of 40 different sandwich recipes including the production of the ingredients, the sandwiches and their packaging, their retail, transport and waste management. They found that the carbon footprints of pre-packaged sandwiches are larger because of the additional energy required for refrigerated storage, the resulting leakage of refrigerants, and the higher food losses that occur throughout the supply chain.

Biggest offender

The team also ranked the worst offenders and found that Mother Nature’s least favourite sandwich is the ready-made ‘all-day breakfast’ at 1441g of CO₂ equivalent. This equates to driving a car 19 km. The most responsible is an egg mayo and cress ready-made sandwich, which has 739g of CO₂ equivalent.

The results show the largest contributor is the farming and processing of their ingredients, which account for 37%-67% of the carbon footprint for ready-made sandwiches. Preparation and refrigeration can account for up to a quarter of emissions. The packaging material comes in at up to 8.5 % and, finally, transport adds around a further 4%.

Study author and IChemE Fellow Adisa Azapagic said: "Given that sandwiches are a staple of the British diet as well as their significant market share in the food sector, it is important to understand the contribution from this sector to the emissions of greenhouse gases.”

“For example, consuming 11.5bn sandwiches annually in the UK generates, on average, 9.5m t of CO₂…equivalent to the annual use of 8.6m cars.”

A greener lunch

Seeking to make our sandwiches greener, the authors recommend reducing or omitting ingredients that have a higher carbon footprint, like lettuce, tomato, cheese and meat. Reducing ingredients, such as cheese and meat, would also reduce the number of calories eaten, contributing towards healthier lifestyles.

Furthermore, the study finds that the carbon footprint could be cut as much as 50% if a combination of changes were made to the recipes, packaging and waste disposal. The researchers also suggest extending sell-by and use-by dates to reduce waste.

“We need to change the labelling of food to increase the use-by date as these are usually quite conservative,” said Azapagic. “Commercial sandwiches undergo rigorous shelf-life testing and are normally safe for consumption beyond the use-by date stated on the label.”

Sustainable Production and Consumption: http://doi.org/cjt5