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The mathematics of milk

March 24, 2010

There are three people in this household who drink semi-skimmed milk: myself, J, and Graham. We all drink it, it goes into sauces and rice puddings, and also onto cereal. Yet it is a source of continuing fascination-cum-bemusement to the resident skimmed-drinker, Rhiannon, just how much of it we go through. Empty green-top bottles seem to appear basically from nowhere.

So in the interests of SCIENCE!, being the pathologically curious ex-physicist he is, J decided to start keeping track of how much milk appeared and disappeared in the fridge, and has now presented me with a result.

The three semi-drinkers have, between us, accounted for 20 pints of milk in the last week.

Now it turns out that 20/7 – as well as it being my birthday – has the interesting property that, if you stick it into Google, the first result you get is Revelation 20, verse 7:

And when the thousand years are expired, Satan shall be loosed. The earth shall have its golden age, but it shall not last forever.

Which threw me a little bit, shall we say. (We shall not have milk forever! Enjoy your protein- and calcium-rich luxury while you can!) But the Google also kindly informed me that 20pts/week works out to a considerable 2.86 pints per day, or 0.95 pints per person per day.

Naturally my first thought was ‘How many cows is that?’

The FAQ of Dairy Farming Today tells me that a cow gives 6-7 US gallons of milk every day. A US gallon, according to Wikipedia, is just under 3.79 litres. Multiplying this by 6.5 gives 24.61 litres per day. Now a litre is 1.76 pints, which makes the total output of a dairy cow a staggering 43.3 pints a day, or 303.09 pints a week!

So not very many cows at all, in fact. We are consuming between us a paltry 1/15th of a cow’s output (cowtput?), or 1/45th of a cow each.

Now the UK has ‘just over 2 million’ dairy cows, according to DEFRA, supporting a population of about 61.38m in mid-2008. Call it thirty people per cow, in any case. So it appears that we are consuming one-third less than we ought to be. (1/45 = 2/3 of 1/30). However! No doubt the UK exports. How much milk does your average Briton actually consume?

DEFRA once again provides, informing me that

Average liquid milk consumption for 2008 stands at 1,555mls per person per week

and that the trend is generally towards consuming less, which one might presume to have held over the last two years. But the curse of differing measurements strikes again – how much is 1,555ml, anyway? 1.555 litres is 2.74 pints.

Now 20pts a week between 3 people works out to 6.67pts each. It turns out that each of us is in fact consuming no less than 2.43 times the national average. Possibly a bit more, if average milk consumption has dropped since 2008.

That is a somewhat staggering figure, even to me. It is a strange and somewhat lonely feeling to know that I by myself have the weekly milk intake of 2.43 people.

This is, however, something I can blame on my parents, who took great pains to get myself and the assorted younger siblings drinking plenty of milk when we were small in the hopes of our avoiding osteoporosis when we age. (Sorted that one, surely. 2.43 times as much calcium intake must mean I have bones of PURE LIMESTONE.) And I never got out of the habit. Which means that I am probably set in my ways for the rest of my life now.

I was born in 1989, which according to National Statistics means I have a (conservatively estimated) life expectancy of around 78. Assuming for the sake of mathematics that I live to exactly 78 (I get to see Halley’s Comet! And throw my ‘1000 years of Not Being Invaded!’ party!), this means I have 2,980 weeks to live, counted from yesterday (my birthday this year is a Tuesday).

2,980 weeks of life at 6.67 pints of milk a week indicates that I will consume 19,866.67 pints of milk in my remaining lifetime. That is, for want of a better term, A STUPID AMOUNT.

A six-pint bottle of milk currently costs about £2.40, or 40p a pint. This makes that over the course of my remaining life I will spend at least £7946.66 on milk. This is also A STUPID AMOUNT.

On which note, I need a drink. Of milk, naturally.

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3 Comments leave one →
  1. knightofthedropdowntable permalink*
    March 24, 2010 4:44 pm

    For the purposes of SCIENCE!, I now feel that I should repeat my experiment, as many times as possible, and possibly keep a note of the results week by week. Which is mildly annoying, as it was only by accident that I noticed we had used 20 pints in a week. Probably should have kept it to myself!

  2. Paul Skinner permalink
    March 24, 2010 4:58 pm

    One final calculation:

    Given your calculations you will have used 15.9% of a single cow over the rest of your life.
    (Or 4/25ths)

    Cows (apparently) produce around 18,750 US gallons in their lifetimes.
    That’s 70,976.47 litres.

    19,866.67 pints = 11,289.46 litres

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