4% of 568 is 22.72. Hold on to that thought.
A ‘unit’ of alcohol is actually 10 ml; if you’re a man, your recommended weekly dosage amounts to a bit less than a pint of gin, or rather more than half a pint of cask strength whisky, or rather less than half a pint of pure alcohol. Don’t drink it all at once.
But what, I hear you ask, what about beer? I refer the honourable reader to the answer previously supplied. A pint of bitter at 4% alcohol by volume will contain 22.72 ml of alcohol, or slightly more than two and a quarter units. Two and a quarter isn’t all that handy as figures go, but it’s a lot handier than 2.272. Apart from anything else, two and a quarter translates nicely to the improper fraction 9/4, which is handy. Say, for the sake of argument, that you want to know the strength (in ‘units’) of a pint of something at 4.5% a.b.v. (e.g. the Marble Brewery’s renowned Ginger Marble), or indeed something at 6% (e.g. the Marble Brewery’s hard-to-find Special Ginger Marble, which I tasted last Friday). Simple: all you need is fractions. First you calculate the ratio of 4.5% to 4%, which is (9/2) / 4; invert the second term to get 9/2 * 1/4; multiply out to get 9/8. Then you just need to multiply that original 9/4 – the number of ‘units’ in a pint of 4% a.b.v., you’ll remember – by the 9/8 ratio; you end up with 81/32, which is as near as dammit 80/32 or 5/2. Two and a half units, in other words. (For the 6% the ratio is 6/4 or 3/2, meaning that when you multiply out you get 27/8, or nearly three and a half.)
This, I’m sure you’re saying at this point, is all very well, but what about situations when I may want to sample a wide variety of drinks of different strengths? What if I were to visit the Stockport Beer and Cider Festival, whose programme boasts an impressive 120 beers, a startling 34 ciders and a frankly alarming 18 perries? (This isn’t advertising – the festival was last weekend.) Oh, you might say, I can always carry on drinking while I’m feeling pleasantly drunk and stop when I start feeling unpleasantly drunk, but experience warns that this may not always be sufficient to ward off inebriation-related mishaps such as stopping for ghastly fast food on the way home, stopping for a drink on the way home (how could that have been a good idea?), falling asleep on the bus and ending up in Bolton, feeling thoroughly ill for the rest of the weekend, etc. To which I reply, think of the units. Let’s say, for the sake of argument, that you know from experience that three pints at 4.5% is a decent evening out, four pints is chancy for mid-week, five is a bit rocky the next day and six is definitely too much of a good thing. (I do remember managing seven once; I don’t remember how I got home, though.) Then multiply out by the units, two and a half per pint. So ten is fine, twelve is time to slow down and if you reach fifteen you should have stopped already.
Then – and this, frankly, is the clever bit – you work out what concentration of alcohol you’d have to be drinking to reach your selected limit in half a pint. We know that a pint at 4% contains 9/4 units, from which it follows that half a pint contains 9/8. So to get ten units in half a pint, the level of alcohol by volume would need to be (10 / (9/8)) * 4, or 10/1 * 8/9 * 4, or 80/9 * 4, or as near as dammit 9 * 4: 36%. Then all you need to do is tot up the percentages of the halves you drink (no shame in drinking halves at a beer festival; most of the people there were drinking from lined half-pint tankards), and stop when you hit 36. Or, if you’re aiming for 12, do the whole thing again and… stop at 42.
I worked all that out in the stands at Edgeley Park, gazing into the distance and vaguely trying to separate out crowd noise, traffic noise and aeroplane noise, between a half of the aforesaid Special Ginger Marble and one of something with the uncompromising name of Blackcurrant Stout. (Unfortunately, this tasted exactly like you’d expect, say, Murphy’s and black to taste. I can’t say I wasn’t warned.) In the event I was slightly disappointed by the beer range, although I can’t quite put my finger on why. On one hand, the range was just too big – you might not go in expecting to sample everything, but with 120 beers on offer over three days even the most dedicated ticker would have to leave the great majority untasted. And you’ve got to try a rarity like the Special Ginger Marble, and the odd novelty, and the odd strong beer like Phoenix Earthquake (7.3% and very nice indeed), not to mention the odd cider or perry – and how many bitters does that leave room for? At the same time, the mainstream ales were very big on the hoppy style and rather light on the darker, more malty bitters. All very Manchester – rather more Manchester than Stockport, in fact – but still a bit disappointing. I felt alternately spoilt for choice and stuck for choice. On the cider and perry front, on the other hand, spoilt was the word. I ended up skipping the cider and trying two perries, in one case because I was intrigued by the name: Stinking Bishop. All rapidly became clear: the taste is interesting – not unpleasant if you don’t mind being reminded of ripe Brie while you’re drinking your perry – but the smell… Yes, this is in fact a perry which stinks. Well done, Minchew’s. The Blakeney Red perry from Gwynt y Ddraig was rather fine, on the other hand, despite the name of the brewery translating as Dragon’s Fart. There must be something about growing pears that brings out a sophisticated sense of humour.
I worked all that out – and I stopped at 35.7, because I’d been feeling tired – but I only realised much later that most of the calculations had been completely wasted. Let’s say that I’m aiming for the equivalent of four pints at 4.5%; to find the half-pint equivalent, I just need to multiply 4.5% by the ratio of four to a half, or 8. So you can get to the same result with a lot less mental arithmetic. But really, where’s the fun in that?