The carbon footprint of your sandwich

If, like me, you wonder about the environmental impact of your food choices, you’ll be glad to know that some dedicated academics at the University of Manchester have recently published work on the carbon footprints of a whole range of sandwiches. [if you’re not like me, then I guess you won’t be reading this blog anyway].

We are a nation of sandwich eaters. Apparently we consume 11.5 billion of them each year, about 174 each. Around half of these are made at home, with the remainder bought pre-packaged. The authors of the study have looked at 24 of the most common filling choices for pre-packaged sandwiches, and 16 of the most common sandwiches made at home. I didn’t know there was a British Sandwich Association until today, but they seem to know a lot about what types of sandwiches we like.

sandwiches1

The first thing that struck me when reading the paper was how unhealthy our sandwich choices are; 70% of what we buy contain meat, cheese or fish. And we also seem to like mayonnaise; only 2 out of the top 20 eaten sandwiches didn’t have any mayo in.

The next thing of interest was the relative importance of the ingredients, compared to the impacts of preparation, refrigeration, packaging, transport and waste management. The carbon footprint of the ingredients ranged from around 250g CO2 equivalent (egg mayo and cress) up to 1kg (all day breakfast). The rest of the production-supply-disposal chain is around 400g CO2 equivalent per sandwich.

So what does a low carbon sandwich look like? The best five were egg mayo and cress (739g CO2 equivalents), chicken and sweetcorn (769g), tuna and sweetcorn (852g), egg and rocket (854g), chicken and mayo (887g). The worst sandwiches were the all-day breakfast (1441g CO2 equivalents), the ham and cheese (1350g), prawn and mayo (1255g).

It’s probably fair to say that as with all life cycle assessment studies, there is a risk of being misled by the precision. But the paper also includes a sensitivity analysis (which is a scientific way of working out how much it matters if some of your starting numbers were wrong), and for over 40 alternative scenarios, nothing changed the end result by more than 14%.

Turning to the homemade sandwiches. All but the worst 3 analysed had lower impacts than even the best performing pre-packaged sandwich. This is largely due to lower impacts in preparation, food waste and refrigeration. The amount of ingredients we use seemed to differ quite a lot from pre-packaged sandwiches (the data suggests we are much stingier than the retailer), and this also contributes to the lower impact of homemade sandwiches.

Take home messages from all of this are:

  • Don’t buy pre-packaged sandwiches if you can avoid it; almost all the homemade sandwiches had lower impacts than even the best performing pre-packaged.
  • If you’re going to buy a pre-packaged sandwich, the lowest impact main ingredients are egg, tuna, chicken and cheese, in that order.
  • Packaging waste doesn’t matter (0.8-1.3% of the total impact).
  • Food waste does matter. The major impact of most sandwiches is in the ingredients. Don’t buy a sandwich if you’re not going to eat it!
  • Vegetarian’s shouldn’t feel particularly smug. Chicken has a lower impact than cheese.

In case anybody was wondering, my favourite sandwich is cheese and gherkin. I also like hummus. Sadly, neither was analysed in this study.

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