Only one was allowed in, and rightly so. Although the two common types look similar, they are about as closely related as birds and bats (not very). Sweet chestnuts, Castanea sativa, are delicious and nutritious while the horse chestnuts, Aesculus hippocastanum, will give you diarrhoea or worse.
But don’t fear, they are easy to tell apart. The good variety have a distinct spike on top, while the ones to avoid are bulbous and misshapen.
In any case, you’ll know you’ve got it wrong if your chestnuts taste distinctly bitter, making it unlikely you’ll eat enough to get too sick. The perception of bitter taste is an adaptation specially to help us to avoid toxic compounds which might be naturally occurring in a food, or a byproduct of rotting. Unfortunately the system is not perfect – some bitter foods like spinach and grapefruit are good for you, while some really nasty ones like the death cap mushroom taste fine – but it will at least help you pick the right chestnuts.
Gathering these was made memorable by two kids who were completely intrigued by what I was doing. They left, and a few minutes later came whizzing down the hill with some nuts they had found, asking how to cook them. I have added the trees I found to the Food and Fruit Share Map, but I may have got the last ones for the season.
To prepare them, cut crosses in the skin of the chestnut then roast on a tray for 30 minutes at 200°. Piercing the skin allows water vapour to escape as the nut warms up, and making a cross shape makes them much easier to peel.
They went down a treat in my office, and were so easy. Well worth doing again.