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Hydration Math

January 9, 2013 - 8:14pm
shoshanna673's picture
shoshanna673

Hydration Math

Hi

I am new to sourdough and am struggling with hydration math!  Can any kind poster help me with a few dumb questions?  I have an established white starter at 65% hydration.  I have not yet baked with it and am now ready to take the plunge.  For my chosen recipe (Emmanuel Hadjiandreou's Seeded Sourdough) I require 160g of starter.  Can someone tell me how to build some starter for baking at 65% hydration (2 feeds at 12 hour intervals?) to arrive at this 160g.  I know, I'm dumb!!  The recipe does not specify a particular starter hydration.  Also, is it possible to change the hydration of my mother starter, and if so, how would I do this?  Or can I just bring the hydration up as necessary for different recipes?  I have a new rye starter currently under way, which is 100% hydration.  Don't want to end up with a frig full of different starters.

I am boning up on hydration, having just come to grips with bakers %s.  I will get there.

Thanks to anyone who is willing to help

Sondra

 

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cranbo's picture
cranbo
Jan 9 2013 - 11:11pm

Here's the formula to solve:

flourAmount + (hydration% * flourAmount) = starterAmount

(remember, hydration% * flourAmount represents how much water you need.)

Expressed in alegbra:

x + .65x = 160

1.65x = 160

Thus, x = 97g.

So, 97g of flour. Then 97g * 65% = 63g, meaning 63g of water. 

97g of flour + 63g of water = 160g starter. 

David Mackie's picture
David Mackie
Jun 3 2019 - 8:58am

Here are more formulae that will help.  I actually created an excel spreadsheet (I call it my BreadSheet) to calculate amounts.  For example if I have a 100% hydration starter how much flour and water do I need to get to an 80% final hydration bread.

formulae:  where h=hydration, f=flour weight, w=water weight, t=total weight

(1) h=w/f 

(2) f+w=t,

so therefore from (1) w=fh,  then substitude fh for w  in (2) and we get  f+fh=t

which can be expressed as  f(1+h)=t,

rearranging to calculate the amount of flour we get

f=t/(1+h)

This will calculate the weight of flour required given a total weight and a required hydration.

For example if you need 300g of 80% hydration starter the amount of flour in that starter will be

f = 300/(1+.8) = 300/1.8 = 167 g of flour.  

The amount of water is simply 300-167 = 133.

 

 
cranbo's picture
cranbo
Jan 9 2013 - 11:20pm

Also, is it possible to change the hydration of my mother starter, and if so, how would I do this?  Or can I just bring the hydration up as necessary for different recipes?

Changing hydration of any starter is easy: 

Just reserve 1 heaping tbsp of starter, and then feed by weight according to the hydration you want:

  • 100% hydration will be equal parts flour & water by weight (e.g., 100g flour, 100g water)
  • 65% hydration means that for every 100g of flour, you will need 65g of water. 

etc. Only 1 feed should be enough to change the hydration of the starter. 

You'll need to pay attention to the starter hydration specified in the recipes you use. You have a choice of the following:

  1. create a starter according to the hydration specified using the method described above; or
  2. adjust the overall liquid in the finished dough of the recipe by increasing or decreasing for the kind of starter that you have. You can use Joshua Cronemeyer's hydration calculator to do this. 



David Mackie's picture
David Mackie
Jun 22 2019 - 7:10am