Hydrations hydrations




A simple question/confirmation, must have been asked many times before, I think I did a lousy search. Sorry! :)


I keep my starter at 75% hydration, some recipes call for 75% starter some 100%... for example if I wanted to bake a recipe that called for 200g of 100% hydration starter, and I have around 30g flour - 22g water starter weighing about 55g (give or take with the bits left at the bottom) and I take 40g of this out and refresh it with 80g water and 80g flour to achieve 200g.. I don't get 100% hydration right? and I need to add some more water  or take away some flour? 






95 users have voted.


Paul Zwick 2012 February 20



Based on your info, you will need 8g added to your current starter to bring it to 100% hydration level.


Then add 70g flour + 70g water and this will bring to 200g in total.


Current starter 30g flour       22g water

Add                                          8g water

Add                  70g flour         70g water


TOTAL:           100g flour   +   100g water = 200g  of 100% Starter

farinam's picture
farinam 2012 February 20

Hello olionel and Paul,

As I read it, olionel was asking for the result starting with 40g of his starter so the answer is more like 83g water and 77g flour if you want to be pedantic about the starting weight to use.

Fundamentally, Paul is right, the best way to do the calculation is to work out how much water you have to add to your starter to bring it to the required hydration and then the balance to get to the final weight required.  This is easy for 100% hydration but a little more brain taxing for other target hydrations.

If you want you could check out the spreadsheets that I posted in some earlier blogs.  They don't do exactly this calc but could easily be used to get the answer that you want with a bit of trial and error.

Keep on bakin'


chazzone 2012 February 26

The way I would figure this, would be to start by figuring out the fraction of the starter to be used from your base.  Do this by dividing the starter portion by the base.  40/52=.769  You can then take the known amounts of ingredients to find how much of which is in the starter portion.

So by multiplying 30gx.769 we get our flour and by multiplying 22x.769, we get the amount of water. 40g of this starter has approximately 23g flour and 17g water.

A 200g sponge @ 100% hydration would have totals of 100g flour and 100g water, so we simply subtract each amount from the total, and we have our numbers to add.


100-23g flour=77g flour and 100-17g water=83g water

Hope this helps,






Gene 2012 February 27

Thanks for the challenge, Olionel. That has allowed me to tweak my levain calculations. Up to now, I've always worked with the amount of levain that I had so that I did not have to work towards a targeted levain weight. I adjusted my fermentation period depending on whether I had more or less levain than a particular recipe required. Having encountered no particular problem up to now, I have not felt the need to change the way I calculated my levain builds. Your enquiry threw me back to the drawing board so to speak. I have now tweaked my calculations.

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