Written by Louise Dann, a real actual scientist
Use by dates and the science behind them.

This actually isn’t scientific so much as a personal rant about injustices done to food in the name of health and safety. Having a quick squizz at the Food Standards Agency website causes anxiety that I am about to be litigious but my trusty caveat is that whilst I have a vague but old knowledge of the immune system my in depth knowledge of viruses will give me no expertise whatsoever with regard to food safety and I can happily pronounce I am therefore decidedly un-scientifically qualified in this field. NB viral spread via the sharing of a dodgy kebab of a Friday night probably has happened but not yet in a way as to define this a risk factor.

Use by dates on food wind me up, as does my flatmate’s religious belief in the rapid onset of decomposition and prompt breeding of bacteria come the midnight hour when the food has to be ‘used by’. Everything has, by law, to have a ‘use by date’, not to be confused with ‘sell by’, ‘display until’, ‘keep in the 3 for 2 offer by’, or any other shop orientated date. I presume this use by date is achieved by putting the designated food in a petri dish in the fridge (or most likely storage receptacle) and seeing what happens. I’m assuming then, at every juncture in time, some poor person has to check the food for various criteria, taste, touch, smell until it becomes apparent that something else has made its home in the food and then lab tests take over. Again presumably the average or even lowest time point at which the food reaches a noticeable change threshold, this must become the use by date.

I fully appreciate that some real nasty microbes can rapidly populate your leftovers, and once eaten can illicit some pretty toxic results. My main gripe comes with the foods that don’t need a use by date. A potato for instance. A potato will do many things to let you know of its off-ness. Obvious signs of a potato being a bit over the hill are the shrivelled-fingers-in-the-bath-look, the grey/white fungal coating, green discolouration (which also makes the spud a bit more turgid in my experience), wet brown rotting (least pleasant) and my own personal favourite, the growing of legs (tubers). Depending on the degree of the above the offending symptoms can be removed with judicious use of a knife and the rest of the spud eaten relatively freely. My one warning here is that the green potato has seen too much daylight and has started to photosynthesise. There are rumours that one of the products of a photosynthesising potato is slightly toxic. I dispute this rumour (from my great-Aunty-Muriel) but nevertheless have always peeled these more ferociously and removed the green. My point being that certain things you can happily eat till your own sense of smell, taste, sight etc tell you not to. It’s only when something (like meat) may be frequented by one of the ‘nasty invisibles’ that you need extra help, but surely the general populace have some sense and if not, then here’s a perfect example of Darwinian evolution in the form of a reheated curry and rice (say hello to the impressive rice bacteria Bacillus cereus, responsible for a fifth of the world’s food poisoning). Besides which, cold curry is just as nice as it is when hot.

Which finally brings me onto my gripe – finding that my flatmates have binned entire packs of tomatoes, apples, mushrooms (it’s a bloody fungus already), yoghurt (ditto on the bacteria, really it’s just got more tang), just because their use by date has passed. And yes I have fished these out of the bin to eat (if packaging was still intact).