Thursday, 8 October 2015

More Trouble with Numbers

Many people seem still not to have completely adjusted to our change to metric measurements, so  recipes often give both metric and imperial quantities.

An ounce is about 28.35g, but decimal notation seems to induce involuntary bowel motions in many folk, and that would be most unhealthy in a kitchen, so the writers of recipes try to simplify the arithmetic.

30 grams per ounce is fairly near to the correct value, and its adoption would have been the generous choice, but menu writers often prefer the much meaner 25g per ounce. On the other hand a pound is 453.6 grams, which even the meanest of chefs are reluctant to round down to 400g, so they usually choose 450g. Thus is is possible to have recipes that convert 15 ounces to 375g, and convert a pound to 450g, making the sixteenth ounce worth 75g.

The National Trust recently published a recipe for Apple Raisin and Cider Tea Bread that used four different conversion ratios all in the same recipe, and all of them incorrect.

9 ounces of flour were converted to 225 grams (25g per ounce)
5 ounces of butter were converted to 120 grams (24g per ounce)
4 ounces of sugar were converted to 90 grams (22.5g per ounce)
2 ounces of sugar for the glaze were converted to 60 grams (30g per ounce)

 Note that the conversion of 9 oz to 225g treats 9 oz as slightly less than half a pound, while it is actually a full ounce more than that.

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