This is all based around an excellent video by Fandabi Dosi, aka Tom Langhorne, who specialises in actually living the survival techniques and equipment of Scotland in the 16th Century or so. Multiple uses of the plaid (“the great kilt”), starting fires in a notoriously wet country, that sort of thing.

This particular video is about his take on a Highland survival food. He comes up with his own recipe, which as far as I’m aware doesn’t actually exist historically, but it could well have done, or at least a close variant.

So I tried it…and yeah, it pretty much works as advertised. It isn’t, as he points out, going to win any baking awards, but it’s calorifically dense (my sums say about 1,000 calories a biscuit, so three biscuits a day is a reasonable claim), and they’re definitely edible. More than that, they are one of these foods that feel calorie dense when you’re eating them, if I was massively hungry in the hills this would be a very welcome snack. Not as good as firing the stove up and cooking something substantial, but easily enough to fill me up a bit.

But about that shelf life claim – how long will these things stay edible without refrigeration? Given the ingredients I’m willing to bet on months, and wouldn’t be surprised if it was into the years. Not necessarily “best before”, I can imagine they’ll continue to dry out and may get a little more challenging to eat, maybe needing a soak in water first, as with hard tack / ship’s biscuit, but I’m looking more at the bacterial side: will they be safe to eat, rather than pleasant.

So I cooked some up, have them stored in a cool (not refrigerated) dry place, wrapped in greaseproof paper tied with string (the modern equivalent of Tom’s beeswax impregnated cloth), and I’m going to take a bacterial swab every six months, both from the surface and from the inside of a broken open biscuit, and I’ll see what I can get to grow on an agar plate.

Note for the microbiologists: this isn’t entirely rigorous. I’ll be using standard nutrient agar in aerobic conditions, because that’s the limit of my training and the kit I have access to.

Note for the non-microbiologists: the stuff I’ll be using to grow any bacteria I find is not set up to favour stuff that is particularly harmful to humans, specifically anaerobic food poisoning stuff like botulism. This is entirely on purpose, I’m not trained to mess with stuff like that.

What I’ll be looking at is whether bacteria grow on them more generally. I’ll also be able to pick up moulds and fungi etc, which may or may not be harmful if eaten. See, for example, the blue mould found in many cheeses, and is entirely harmless. Or ergot, a fungus that grows in rye and has similar effects to LSD, but in a far more unpleasant way.