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By Andy Coghlan

As well as saving money, making your sandwiches at home will help save the planet.

Adisa Azapagic of the University of Manchester, UK and her colleagues have studied the carbon footprint of the 11.5 billion sandwiches eaten in the UK each year. They worked out how much greenhouse gas is released by making 40 types of sandwich. Overall, they found that the UK sandwich industry releases the equivalent of 9.5 million tonnes of carbon dioxide.

However, homemade is better. “The main reason is that in commercial sandwiches you have longer refrigeration chains, plus packaging, and waste tends to be higher from bought sandwiches,” says Azapagic.

The most climate-friendly sandwich studied is a plain, homemade cheese and ham sandwich. On average, depending on quantities in in the sandwich, it generates 550 grams of carbon dioxide equivalent, the same as driving a car for 6 kilometres.

The worst is a commercial egg, bacon and sausage “all-day-breakfast” sandwich, with corresponding values of 1440g and 19km. The least harmful commercial sandwich was egg mayonnaise with cress, with carbon footprint figure of 740g, equivalent to driving 10km.

The editor regrets his breakfast choice

The largest contributors are the farming and processing of ingredients, which account for 37 to 67 per cent of the footprints for ready-made sandwiches. Refrigeration in stores accounts for 25 per cent, and packaging 8.5 per cent.

Meat, especially red meats like beef, had the biggest impacts, because of the methane in burps from cattle, and the need to grow food for livestock. This same factor also gave cheese a high impact. “It’s made from milk, which comes from cows, and cows burp methane,” says Azapagic.

For unrepentant carnivores, chicken is the least harmful meat studied. Its impact is five times smaller than beef, because chickens don’t burp.

Azapagic says people shouldn’t ditch sandwiches, as eating them probably has less impact than a full restaurant meal. “You must take the results in context, and this was looking at sandwiches simply to create awareness of their potential impact.”

Journal reference: Journal of Sustainable Production and Consumption, DOI: 10.1016/j.spc.2017.12.002