Last post, we talked about all about the science of starters. While you’re nurturing your culture, let’s take some time to talk about all the recipes you’re going to tackle once you’ve for a healthy starter going. Ladies and germs (or, I should say, lacto-bacteria), may I present: Baker’s Math.

If you’re a math person, get ready to learn a new kind of percentages that just might drive you crazy at first. If you hate math, consider this a chance to finally master something that wrecked your GPA in high school.

Recipes for bread (and beyond) are often written in “Baker’s Math,” “Baker’s Percentage,” or “Flour Weight.” While it initially looks baffling, it’s actually a great way to convert recipes between English and Metric mass systems (ounces and grams) and increase or reduce the amount of bread you’re making.

Before we get there, though, it’s important to clarifying that we’re working with mass, not volume. If you live in the U.S., you probably learned to cook using volume measurements: cups, tablespoons, and teaspoons. Baking in the U.S. can get absurd. Not only do you often have to wash somewhere between 3 and 17 measuring cups and spoons, you’re unlikely to get the same amount of flour when scoop directly from the bag as when you spoon flour into the cup. And don’t even get me started on dividing a recipe that calls for “⅜ cup of sugar” in half. Thanks, Fannie Farmer* (not). If you’re from anywhere else, you probably measure with a scale like a sane person.

Regardless of provenance, bakers tend to use mass for precision. As I mentioned before, you can come by a kitchen scales for as little as $10. If you’re going to do tons of baking and want to save some energy, solar-powered scales run $40 and up. I use a smart Drop Scale that was given to me by the Drop team when I worked for Autostraddle. I love it deeply (I can enter my own recipes into their app to make baking easier), but any scale you can get your hands on will work just fine as long as it measures to the nearest gram or tenth of an ounce.

In baker’s math, everything is expressed as a percentage of the flour. Let’s look at a simple bread recipe written out in terms of mass and baker’s percentage:

Huh? 193%? In baker’s math, the total percentage doesn’t matter. Not one bit. All we care about is how much of each ingredient we have relative to the flour. This means that flour is always always always ALWAYS 100% in a recipe. In this recipe, the amount of water you’ll use (490 g) is 70% of the mass of the flour. Bakers call the measure of liquid content “hydration” and a bread like this “70% hydration.” This means that tiny little blob of dough made with 10 grams of flour would have 7 grams of water. A giant swimming pool full of of dough made with 100 pounds of flour would have 70 pounds of water.

If you’re more of a visual person, take a look at the recipe as a little stack of boxes:

Each box holds the same mass. In the recipe above, each box holds 7 grams regardless of the ingredient that they hold. So 100 boxes of flour is 700 grams and 3 boxes of salt is 21 grams. With me so far?

Baker’s percentage is easier to use than recipes written down as regular percentage or as mass a few reasons. First, it makes it really easy to compare doughs. Written in baker’s percentage, you can tell if one dough is wetter or drier, saltier or sweeter than another.

If I tell you that focaccia dough has a higher hydration than bagel dough, can you tell which of the below recipes is which?

Probably not. But when I write the same recipes in baker’s math, it becomes totally clear that Dough 1 is for a bagel and Dough 2 is for focaccia.

Second, it allows you to adjust recipes to suit your taste, available ingredients, or creativity. Let’s say you really want to make the first recipe we looked at but only have 200 g of flour left at home. When using baker’s math, it doesn’t matter if you’re almost out of an ingredient! Just plug the amount of flour you have into the recipe and calculate.

After making the recipe a few times, you realize that the dough is just a little too wet; you want to decrease the hydration to 65%. Using baker’s percentage, that’s not a problem.

Or maybe you decide it needs something extra: walnuts. After a little research, you notice that lots of recipes for walnut bread call for walnuts at 15% to 30%. This gives you a guideline that’ll let you do a little bit of guessing for this experimental loaf. Let’s say you settle on 25%. To find out how many walnuts you’ll need, just multiply the flour mass (200 g) by 25% (.25).

Now that you know how to translate a baker’s math recipe into a mass recipe, let’s go backwards. This is a good skill to have when you’re trying a new recipe and want to compare it to ones you’ve baked before or when you need to increase or decrease the size of the loaf you’re making. To convert, simply divide each ingredient mass by flour mass (910 g).

I am the queen of simplifying, which is why I use spreadsheets when I bake. Here’s one I’ve created for the recipe we’ve been playing with in this post. Try entering different amounts of flour in the pink box.

You can create your own spreadsheets using google sheets or excel. Column A should list the ingredients. Column B should list the Baker’s Math,expressed either as a percentage (70%) or a decimal (.7). Column C should be written to autocalculate the mass. Leave the flour mass box blank (and consider changing the color so that you remember that this is the most important box), and type formulas in the rest of the boxes in the column. Formulas always begin with an equal sign (=) so that the spreadsheet knows to calculate. Since we’re multiplying flour mass by the ingredient’s baker’s percentage, click or type the flour mass box (C2 in the example), the multiplication sign (*) and then the ingredient’s baker’s percentage box (from the B column in the example). Finally, Column D should list the unit (grams or ounces).

Creating shareable spreadsheets for recipes allows you to easily share recipes with friends who you give your sourdough starter to. It also makes it nearly impossible for you to forget what you baked so you can go back and tweak your recipe based on how each loaf turns out.