Bread recipes for the home baker usually list ingredients measured by volume: cups, tablespoons etc. A recipe for a 1 lb. loaf of bread typically requires 2 cups of white bread flour or whole wheat flour.
A cup may mean the amount that fits in the cup used by the recipe writer and tester. Usually, recipes refer to a standard measuring cup, but standards are different. A US cup is .87 of an Imperial (U.K., many other English speaking countries) cup. An Imperial cup is 1.2 US cups. A metric cup is a quarter liter (250 millilitres) which is .88 Imperial cups or 1.06 US cups.
The amount of flour in a cup also depends on how the cup is scooped or filled.
Measuring by weight is more exact – but converting volume to weight is fuzzy. The Bread Lover’s Bread Machine Cookbook suggests 1 cup of bread flour or whole wheat flour converts at 5 oz. Panasonic suggests, in its bread machine recipes, measuring bread flour and whole wheat flour by weight at the conversion rate of 1 cup = 4.9 oz. There is a range of uncertainty in how the weigh of cup of flour:
- 4.875 (4 and 7/8) oz. = 138 g.
- 4.9 oz. = 139 g.
- 5 oz. = 141 g.
Reinhart (The Bread Baker’s Apprentice, and other books) say 4.5 oz.; he measures differently. 4 and 7/8 oz. (4.875) or 4.9 reconciles to recipes in BLBMC and other recipes that use flour as scooped into a measuring cup. The volume to mass conversion for other flours varies. Millers have conversions for their products – e.g. King Arthur. There are generic conversion calculators and tables but these have to used with care.
The point is to be consistent in measuring. I weigh white bread flour (Canadian All Purpose) and whole wheat flour at 139 g. per cup in a recipe. Scales in ounces go down to 1/8 oz, but not necessarily to decimal fractions. Metric kitchen scales go to the nearest gram. That is close enough for measuring a cup of flour.
Books for home bakers may refer to baker percentage (B%), a method of managing the production of bread. For instance Peter Reinhardt devotes pages 40-45 of The Bread Baker’s Apprentice to this topic. It is a tool taught to professional bakers, and addressed in culinary texts such as Daniel T. DiMuzio’s Bread Baking; An Artisan’s Perspective. For the baker-manager, it is a calculation to scale inputs up or down to create 2, 10, 100 or 1,000 consistent loaves of bread. The assumptions are consistency of ingredients, equipment, energy, working space, and time. For managing production, every ingredient is put into the formula. The formula can be used to build dashboard indicator of the use of a bakery. It is as precise as it needs to be, for how it is used. B% is explained:
- Bread Bakers Guild of America;
- The Fresh Loaf;
- King Arthur Flour;
- Bakers Percentage Revised – The Artisan Net article
- Baker Percentage – Wikipedia Article.
Flour has plant proteins and starch. Water and protein make dough sticky and stretchy. Starch feeds yeast – some is fermented. Starch is the carbohydrate in bread – the thing that makes it food. Flour is the ground product of grains, including flour and meal. All flour is counted to determine Total flour weight, even when flours differ in density and protein content. It is conventional to express the relative amounts of flour as a percentage of the total flour weight (e.g. 50% bread flour and 50% whole wheat; or 90% bread flour and 10% rye flour). It is conventional to count all dry ingredients – which works better for a bakery manager than for a home baker.
The weight of every other ingredient is expressed as a percentage of the Total flour weight. The fluid percentage is called the hydration rate, a scale of how wet, sticky and messy the dough is. Conventionally, only the main fluid counts for the hydration rate. Water or milk.
Milk is nearly all water. Butter has water. Maple syrup, honey and other syrups have some water. Eggs have water. ingredients that contain water are not necessarily counted directly – it involves conversions and extra math. Wet ingredients that containe water may be noted to see if a dough has a higher real hydration rate than a simple calculation implies.
A cup of water is 236.6 grams (in the metric system one milliliter of water is one gram). (An Imperial cup of water reliably converts to 284 grams. A Canadian cup is 224 grams. A metric cup of water is 250 grams.) Engineers may deal with variation of the density of water with temperature, Bakers are not as precise.
A cup of fluid cow’s milk is 244-245 grams according to USDA averages. Whole milk should be 3.25% butter fat. Reduced fat milk products: 2%, 1% and non-fat (or skim) milk. In grams, the water/total weights, per cup:
- Skim 223/245
- 1% 219/244
- 2% 218/244
- Whole 215/244
- Buttermilk (whole) 215/245
1 + 1/4 cups of skim milk has 1 + 3/16 cups (1 cup + 3 tbsp) of water.
The home baker’s trick is reduce water in a recipe by 1/4 cup for 1 cup of honey, when honey is used to replace sugar). The average for honey in the US and Canada is 17 g water per 100 g of honey. A typical pure maple syrup for sale in the US or Canada is 32 grams of water per 100 grams of syrup. A large egg, in the Canadian egg grading system is about 57 g. A large egg contributes 40 g. to hydration – nearly 3/16 of a cup of water.
Water can be calculated by referring the USDA Food Composition Databases. For a Canadian product, the Canadian Nutrient File may have the value. Using the databases takes some practice. not all of the water reported in the data is released from the source ingredient and incorporated into dough. It may be necessary, if the dough is just too dry, to use a teaspoon or two more water to get the hydration right for 2 cups of flour in bread machine.
Yeast means, normally, one of the strains of yeast commercially grown and distributed as a leaving agent. Salt is a chemical control on yeast. B% descriptions of a recipe may have 2% salt and 1% yeast. For 2-3 cups of flour, this means fractions of an ounce of salt and yeast. These ingredients seem to standard commodities – close enough that the brand does not matter for calculating for conversion from a recipe teaspoon to weight:
Table salt 1 tsp = 5.7; but some table salts are fine-grained and more dense
Instant dry yeast 1 tsp = 2.8 g.