June 29, 2017 - 9:04am
Baker's Math
I need to change the hydration of my culture. It is now 87%. How would I figure out the flour and water needed to decrease the hydration to 75%?
So if I took 10g of 87% starter and I wanted to triple the new starter to 30g @ 75% how much flour and water would I use?
I'm not only looking for the answer, I'd like to learn how I can compute this in the future.
Thanks,
Dan
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OK. You've got 10g of 87% starter. If you let "x" equal the amount of flour in that 10g, and 0.87x is the amount of water in that 10g, then ...
1.87x = 10g
so x=5.35g (which is your flour weight) and 0.87x=4.65g (which is your water weight). So you have 5.35g of flour and 4.65g of water.
You want 30g of 75% hydration starter. So let's let "y" equal the amount of flour, and 0.75y equal the amount of water. Then ...
1.75y = 30g
so y=17.14g (which is the total amount of flour) and 0.75y=12.86g (which is your water weight).
You have 5.35g of flour, so you need to add 11.79g of flour (17.14-5.35=11.79).
You have 4.35g of water, so you need to add 8.21g of water (12.86-4.65=8.21).
First, read through the tutorial at King Arthur Flour on baker's percentage. If you are clever with spreadsheets, build a table with all ingredients and base the calculations on the formulas in the tutorial. That works for me; otherwise I get completely lost in the calculations!
of your existing culture would be:
flour = 1 (100%)
water = 0.87 (87% of the flour)
culture = 1.87 (187% of combined flour + water)
So - 10g of your existing culture would break down to 10g divided by 1.87 = 5.35g of flour + 4.65g of water
What you want to get to is 30g total with hydration of 75%, so it would break down to:
flour = 1 (100%)
Water = 0.75 (75% of flour)
culture = 1.75 (175% is combined flour and water)
So, 30g divided by 1.75 breaks down to: 17.14g of flour (100%) plus 12.86g of water (75%)
To get from what you have to what you want, you would need to:
Take 5.35g of flour and add 11.79g to reach 17.14g
Take 4.65g of water and add 8.21g to reach 12.86g
I hope this helps!
EDIT TO ADD: obviously others type faster than I do --- but we got the same results!
I'm working to learn the math above, but I've never been good with formulas. I'm 65 and up until now I've relied on common sense. But I'm going to persevere.
Does anyone have a good link to a spreadsheet that I could plug numbers into?
I've read the above post a dozen times or so and used a calculator while learning the principle. I THINK, I'm starting to make sense of it.
I appreciate your help!
The KAF tutorial is good. On the theory that different approaches work better for different folks, here's a tutorial that I wrote some time ago.
Baker's Math: A tutorial
That's a general baker's math tutorial. Here's one specific to your question about changing starter hydration.
Converting starter hydrations: A Tutorial. Or through thick and thin and vice versa
Hope these help.
Happy baking!
David