Converting Metric Weights for Cooking

Date: 12/16/2003 at 21:50:27
From: Brittany
Subject: converting grams

I'm trying to do a project for school and it's a recipe for baking 
cookies.  In the recipe it calls for 500 grams of flour, 250 grams 
of butter and so forth.  How do I know how much that is?  Since it's 
in grams I don't understand how to convert the measurements.  Can you
please help?  Thanks!

Date: 12/17/2003 at 15:02:33
From: Doctor Peterson
Subject: Re: converting grams

Hi, Brittany.

The best thing to do, especially if you want to actually learn how to 
use the metric system the way it is meant to be used, is to simply use
metric scales and measuring cups.  That's what whoever wrote the
recipe expected you to do!  Even in America most (or all?) ingredients 
are labeled in metric; a package of butter will tell you how many
grams it weighs, and you can figure out what fraction of the package 
you need.

If you need to convert to American units, you can weigh these items in
ounces, converting the 500 grams to ounces to know how much to weigh.
 We have information on conversions in our FAQ.

If you don't want to weigh at all, but to use volume measurements for 
flour, for instance, as we usually do in America, then you will have 
to find the density of flour.  There may be tables you can find that 
tell you how many cups it takes to make a kilogram of various kinds 
of flour.

I have often been curious about how European cooks actually measure 
something like this.  Do they put a bowl on a scale and pour in flour 
until it weighs the right amount, or do they know that a certain cup 
full weighs some number of grams (in effect knowing its density, or 
using a cup calibrated for that density)?  So I searched the Internet 
for information on metric cooking.  Here are some of the sites I found:

  Metric Recipes and Recipe Conversion
    http://www.jsward.com/cooking/index.shtml 

This site tells how to cook in metric.  On the "cooking with metric" 
page, it shows how to use a scale--you add solid ingredients, measured
by weight, directly into the bowl until the weight has increased the
right amount.  (It doesn't say what to do if you pour in too much!) 
Liquid ingredients are measured by volume in a separate cup, as usual.
 They also explain why cooking by weight is both more accurate and neater.

On the "conversion basics" page, they list the density of various 
ingredients.  A cup of flour weighs about 110 grams, so 500 grams is 
500/110 cups, or 4.5 cups.

  UK metric association
    http://www.ukma.org.uk/cookery/quickguide.html 

This also advises that you learn to cook in metric, and gives some
basic principles.  They also have recipes, which seem to be built 
around standard package sizes (avoiding the need to measure at all) 
and "mugs" for measuring liquids and flour--not so very metric after all!

  Converting Recipes from Volume to Weight
    http://www.ochef.com/895.htm 

Despite the title, this page advises you, again, NOT to try
converting, but to "get a scale and join the rest of the world.
Otherwise, you would have to have an endless conversion chart for the 
weight of a given volume of every ingredient on earth.  We do not have 
the patience to create such a chart."  It does mention in passing that 
"A cup of flour can weigh anywhere between 3.5 ounces and 6 ounces, 
depending on the type of flour and how it has been packed."

  Chef Rick: Weights and Measures
    http://erazo.org/chefrick/ingredients/weights.htm 

This page, which is not particularly positive on the metric system but
does point out the advantages of measuring by weight, says

  Bakeries, therefore, always measure dry ingredients by weight.  And
  in metric countries (just about the rest of the world), recipes
  usually call for solid ingredients by weight (g and kg) and liquid
  ingredients by volume (ml).  Even so, home cooks usually estimate
  by volume and adjust as they go along.  In Italy, where they make a
  lot of homemade pasta, cooks use a large measuring cup that has
  two graticules, one in grams (weight) for flour and the other in
  ml (volume) for liquids.

So it is possible to make assumptions about the density of an
ingredient and use a cup marked according to that density.  That
doesn't help you, though, if you can't find such a cup for your flour!

But he gives a rule of thumb:

  Flour, cornstarch, confectioners' sugar, and other powdered
  ingredients (such as dried spices) need a separate rule of thumb,
  which I call the 3/5 rule.  For these ingredients, the density is
  approximately 9 grams (1/3 ounce) per tablespoon, as opposed to
  15g (½ oz) per tablespoon for most other denser ingredients.  So
  for powdered ingredients, remember the 3/5 rule to convert dry to
  liquid volume (or the 5/3 rule to convert liquid to dry), and
  also keep a scale handy in case of large quantities (as in 
  bakeries and ships) or extreme days.

So your 500 g of flour would be about 5/3 of 500 mL (the volume of 
water that weighs 500 g), or 833 mL in a measuring cup.  He tells us 
this is 3 1/2 cups (which is correct).  But it disagrees with the 
information I found above.

The bottom line: if you possibly can, try to use a scale, so you 
don't have to decide whom to believe!

If you have any further questions, feel free to write back.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/