Up front admission: I use the metric system in the kitchen whenever I can. I also weight as many of the ingredients as I can. I realize that there are still good and valid uses for volume measurement in baking, as noted below, I just prefer to do as much of the large- and medium-scale measurement in most recipes in metric weight units.
Bakers in the United States need to know about two different measurement systems: English and Metric. The English system is the familiar system of ounces, pints, gallons, yards, pounds and miles. The metric system is grams, meters, hectares and liters.
The English system of weights and measures grew over time. The surviving examples of the system all trace their origin back either to a traditional way of measuring something or to an edict of the king. There are several systems, one for weights, one for liquid measure, one for dry measure and one for distance. The relationships between the various units are ad hoc, they just grew up that way, if you will. The real problem with the English system is that it is a mess. It is very hard to scale recipes up or down and units with the same name can mean different things. For example, one ounce seems simple enough. It's a stingy shot of Scotch, it's the standard unit of gold, it's what toothpaste is sold by. But these are all different units and weigh different amounts. One is a fluid ounce, one is a Troy ounce and one is an avoirdupois ounce. Add in things like teaspoons, tablespoons, pints and pecks and one can become hopelessly confused in no time at all.
The metric system arose in the 1790s in Revolutionary France. The people in charge thought that everything should be rational and logical. They changed the names of the months and rearranged the calendar. They rationalized the king's head and the heads of 50,000 of his former subjects. They looked at the chaotic state of weights and measures in France and decided that there had to be a better way to do things. They came up with a "scientific" system based on units in powers of ten, so that every weight unit, for example, was 10 times or one-tenth the value of the one next to it. The three main units were grams, meters and liters. They used standard prefixes to indicate relative scale and devised a simple, elegant system that has stood the test of time, with only a few variations in the "scientific" standards. Today, most of the world has had the metric system imposed on it, and things seem to function pretty well. One can travel from one end of the earth to the other and be assured that 200 grams of cheese, 500 grams of bread and a liter of wine is exactly what you think it is: a good start to a picnic.
All well and good, I hear you say. What the blazes do I do with my Elizabeth David bread book when she cites soup spoons, teacups and dashes? Or with just about any cookbook from the US that cites cups, teaspoons, ounces, etc.? The question really is should the baker continue to use volume or should everyone use weight? How can one convert from volume to weight?From English to metric?
Here are some places to start.
You can use these conversions to change a recipe from one system to the other, change from English to metric, and scale a recipe up or down correctly.
But a cup of flour defies all logic. A recipe may call for 6 cups of flour, or 4 1/2 cups of flour, or some other number of cups of flour without telling anyone what they mean. The truth is that a cup of flour can weigh anywhere from 4 ounces to 8 ounces, depending on how it's packed and what kind of flour it is. As a result, the baker is left in the dark as to what he should do. Here's what I do: Forget cups and do everything by weight. I've gone a step further and now use the metric system as much as possible. Whenever I start a recipe that specifies flour in cups, I assume that a cup of flour weighs 4.5 ounces. If I have an idea of what the hydration of the dough should be, I make any corrections to my assumption. All in all, I've found that 4 1/2 ounces is a good starting point for a cup of flour. When I get the recipe where it works for me, I note the metric units and go with them the next time I make that recipe.
The small ingredients, salt, yeast, sugar, malt syrup, spices and herbs, are usually better measured by volume. It's very difficult to get these things to weigh accurately on most scales, and most cooks and bakers are more used to thinking in terms of teaspoons and milliliters for these things. If you want a little grin, weigh a tablespoon of sugar and a tablespoon of salt. Then weigh a tablespoon of yeast. My scale isn't accurate enough to get these things right, so I use volume, unless I'm making auch a large enough batch that the scale will work properly.
So the answer to the question of whether or not a baker should abandon volume measure in favor of weight measure is a resounding "maybe."
Also called "How to Make Sense of a Poorly Written Recipe"
Let's look at a very simple recipe, one for French Bread. The recipe is made to 60% hydration and is a 60-2-1 formula. This is a measure of flour, 60% as much water by weight as flour, and 2% and 1%, respectively of salt and yeast as there is flour. I admit, this is a bit of a straw man, in that this is a very easy example, but bear with me, the principles apply to any recipe and to any change in batch size.
| Ingredient | English Amount |
|---|---|
| HK Flour | 7 cups |
| Water | 2 1/2 cups |
| Salt | 1 Tablespoon |
| Dry Yeast | 1 packet |
The first place to start is to note that 20 ounces of water by weight will hydrate a little over 33 ounces of flour. (33 X .6 = 20) If we figure 4.5 ounces per cup, then 7 cups is 31.5 ounces, a little under the 60% number. If the recipe makes sense, then the author is telling you that a cup of flour weighs 33.3 / 7 = 4.75 ounces. This isn't a huge difference, but it is worth noting, especially if you will be making other breads from the book.
Salt and yeast are fairly easy. If you weigh a tablespoon (15 milliliters) of table salt, you'll get about 3/4 ounce. 3/4 ounce is about 21 grams. A packet of yeast weighs 1/4 ounces or 7 grams. (It says so on the packet.)
If we convert the 33.3 ounces of flour to grams, we get 33.3 X 28.4 = 945.72 grams, or 945 grams.
The 20 ounces of water converts to 20 X 28.4 = 568 grams, or 570 grams.
The hydration is 570 / 945 = 60.3%, which is close enough to 60% to be workable.
The salt is 21 / 945 = 2.2%, again, close enough, although if your scale is accurate enough, you could go to 20 grams. It's worth noting that "sea salt" frequently has larger grains than table salt, so that a tablespoon of "sea salt" may weigh slightly less than a tablespoon of table salt. The funny part of this is that all salt is sea salt. Including the stuff they spread on the roads in the winter. As The Yogi would say, "You could look it up."
The yeast is 7 / 945 = 0.75%, which will work in just about any recipe. Again, if your scale is accurate at these levels, you could go to 9 grams and be really close to 1%.
Here's what we've come up with:
| Ingredient | English | Metric | Percent |
|---|---|---|---|
| Flour | 7 cups | 945 grams | 100% |
| Water | 2 1/2 cups | 570 grams | 60% |
| Salt | 1 Tbsp | 20 grams | 2% |
| Dry Yeast | 1 packet | 7 grams | 1% |
Which method do you find easier to work with?
Suppose that you wanted to make a small batch, say half this amount. All you would have to do is cut each amount in half. With the metric system, this is easy, if you accept a bit of rounding.
| Ingredient | English | Metric | Percent | 1/2 English | 1/2 Metric |
|---|---|---|---|---|---|
| Flour | 7 cups | 945 grams | 100% | 3 1/2 cups | 475 grams |
| Water | 2 1/2 cups | 570 grams | 60% | 1 1/4 cups | 285 grams |
| Salt | 1 Tbsp | 20 grams | 2% | 1/2 Tbsp | 10 grams |
| Dry Yeast | 1 packet | 8 grams | 1% | 1/2 packet | 4 grams |
Since this is a simple recipe, it's almost trivial to convert and expand. If the recipe were more complex and you wanted to do some other multiple, the English system would quickly drive you to drink. (That's not all bad, especially after a lot of time in the kitchen.)
The bottom line here is that the metric system is easier to work with and more accurate. I prefer the romance and history of the English Traditional system, but it makes life in the kitchen much more difficult than the metric system.