Sourdough Maths II

A while ago, I posted Note to Self … Sourdough Maths about how to calculate the quantities of ingredients to covert a yeast bread recipe to one that uses a sourdough starter. Of course, this is a very general guide, not a hard-and-fast rule since there are any number of factors that come into play when making bread that deal with ingredients and environmental conditions. Maree from Around the Mulberry Tree (who is a superb sourdough bread baker/teacher and the inspiration behind the Sourdough Baking Australia Facebook group) commented that she now uses baker percentages – also known as baker maths.

I’d remembered reading about baker percentages in a wonderful book by Daniel Leader, Local Breads, and got it back off the shelf and re-read the chapter. He discusses – in plain and understandable English – many other details involved in bread baking, so it was definitely worth reviewing.

But, for this post, I’m going to concentrate simply on Baker Percentage. Also, I have to stress that metric weights are used – not volume (like cups and tablespoons). I’ll start with this calculation from Wikipedia:

I know this might scare off a few of you who don’t feel comfortable with math, but it is simply a formula that shows the individual ingredients in a bread recipe in relation to any given weight of flour (which always equals 100%). I’ll take my sourdough focaccia recipe (converted from Richard Bertinet’s in his book Dough) and convert it to baker percentage.

Sourdough Focaccia Ingredients
(minus the additional olive oil,
rosemary sprigs and coarse salt)
Metric Measurements
(from my Recipe)
Converted to Baker Percentage
(based on 400g flour = 100%,
rounded to one decimal point)
Flour 400g 100%
Coarse semolina 20g 5%
Sourdough starter 225g 56.3%
Salt 10g 2.5%
EV olive oil 50g 12.5%
Water 200g 50%

Start with the an amount of flour – your 100%. Here, the advantage of using baker percentages comes into its own. It means that you can automatically calculate all the other ingredients by their percentage relating to the amount of flour. Note that the additional olive oil, rosemary sprigs and coarse salt in the original recipe are the finishing touches also need to be adjusted, but this is by eye, not measurement.

The following are two examples: first, if I had a kilogram (1000g) bag of flour and wanted to use the whole thing to make an extra-large focaccia or several smaller ones using the whole bag, or second, if you only had about 200g of flour and wanted to make a small focaccia.

Ingredient Baker Percentage Metric Weight: large Metric Weight: small
Flour 100% 1kg (= 1000g) 200g
Coarse semolina 5% 50g 10g
Sourdough starter 56.3% 563g 113g (rounded up from 112.6)
Salt 2.5% 25g 5g
EV olive oil 12.5% 125g 25g
Water 50% 500g 100g

The same proviso stated in my first post on sourdough maths applies here – variations in flour (such as protein content & absorbency which affect gluten-producing properties), other ingredients (which affect texture and consistency) and climate (hot, cold, moist, dry…) will come into play and affect the weights. These are simply guidelines.

A professional baker will know his or her ingredients and baking conditions and know how much flour to use to make a loaf or a basic number of other baked goods. So, Baker Percentages come in handy when calculating for the number of loaves, rolls etc. that are required.

It is really very simple once you grasp the concept that the weight of the flour is the key. And, a calculator helps.


  1. Yup, I’m definitely one of your readers who is uncomfortable with maths. I think I need a strong cup of coffee first – but I will get to grips with this. Thanks


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