The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Sponge Hydration Question

doughooker's picture

Sponge Hydration Question

I need a check of my baker's math, please.

These come from the sponge formulae posted by doc.dough for Larraburu and for another SF bakery.


100 parts flour

50 parts water

50 parts previous sponge


100 parts flour

46 - 52 parts water

100 parts previous sponge

My question is, does the Larraburu sponge have a final hydration of 50%, or does the addition of 50 parts previous sponge alter the calculation?

Same with the "other" sponge: a final hydration of 46% - 52% depending on the amount of water used?

Thank you.

hreik's picture

Sponges alter the hydration, at least that's how I figure it:

Larraburu: If previous sponge is 50/50 (water flour): than the final result is Flour 125, water 75 so 60% hydration.

"Other": if sponge is 50/50 then assuming water is 46-52% then final is: 150 flour 100 water, so final is  64% -  68%

It's late though so maybe my calculations are off.


doughooker's picture

"Larraburu: If previous sponge is 50/50 (water flour): then"

Right, but previous sponge = 50f/50w/(50 previous sponge).

Confusing, isn't it?

doughooker's picture

According to doc.dough,

"the stored sponge is refreshed at ratio of 1:1:2 [sponge: water: flour] (which produces a new sponge at 50% hydration)."

mikedilger's picture

I think it would be odd if the current sponge hydration was different from the previous sponge hydration.  The hydration at which the current sponge would equal the hydration of the previous sponge is 50% (for Larraburu)

Equasion 1:

new_hydration = old_hydration

(50g + prior_sponge_water) / (100g + prior_sponge_flour) = prior_sponge_water / prior_sponge_flour

Equasion 2:

prior_sponge_water + prior_sponge_flour = 50


Two equations, two variables.  You do the math.

You don't actually have to make it this complicated though.  In cases where the hydration remains constant, you know that the incoming dough has the same hydration as the incoming starter, and that is 50/100.

doughooker's picture

"I think it would be odd if the current sponge hydration was different from the previous sponge hydration."

That about sums it up.

Abe's picture

But it makes more sense that extra sponge is made each time for the next batch and so on. In which case previous sponge is the same hydration as the current feed which would make it 50% hydrated.

In the second example you will get a small variation each time with the hydration changing by a small percentage each way depending on the previous sponge and what it's fed.