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Wet Starter v. Firm Starter and Hydration Percentages

hydestone's picture

Wet Starter v. Firm Starter and Hydration Percentages

For the past month I've been working on a new sourdough starter and it is doing well.  I used the rye flour and pineapple juice method described in the handbook.  I've been mixing 1/4 cup starter, 1/4 cut of flour and 2 T of water each day for the past week or so.  I am going to make the San Francisco stlye sourdough in the lessons section.  It requires 300 g of starter and I don;t have that much.

I read in the starter maintenance section of the handbook to use 1/4 c starter, 1/2 c flour and 4 T water.  I wanted to make sure I had some left over to keep growing so today I mixed 1/2 c starter (everything I had) 1 c flour and 8 T of water.

I changed the ratio from 1/4 c starter:1/4 flour:2 T which I used to grow the starter.  Now I have 1/2c starter:1 c flour: 8 T water.

I am trying to figure out:

What ratios do I use when I want to produce larger quantities of starter to bake with?

How does % hydration work?  I thought 100 g flour with 50 g water = 50% hydration.  I am not sure how it works with a starter.

How can I take a wet starter and make a starter with 66% hydration?

I am going back to using a scale to bake and getting away from cups and T for a bit more accuracy.



dmsnyder's picture

Hi John.

First, do weigh ingredients, even when feeding your starter.

Second, you are correct regarding how hydration is calculated. In fact, the baker's percentage of any ingredient is represented by the formula:

(Ingredient weight/Total flour weight) x 100 = Baker's % of Ingredient

So, if Ingredient = water, then Hydration = (Water wt./Total flour wt.) x 100.

When changing the hydration of a starter for a particular recipe, usually the amount of your seed starter is small enough that the seed starter hydration need not be accounted for. (If you are computing everything to 3 decimal places, please don't let me stop you from factoring in the actual amount of water and flour in your seed starter.)

So, take the final starter feeding specified in the recipe you are using and ignore your seed starter hydration.

How can I take a wet starter and make a starter with 66% hydration?


10 g Active Starter (of any hydration between 50 and 125%)

30 g Flour

20 g Water

This will yield 60 g of 66% hydration starter.  Note that the difference in the water content between 10 g of a 50% hydration starter (very firm) and 10 g of a 125% hydration starter (very liquid) is approximately 1 g. (1 g/60 g) x 100 = 1.67% difference in your starter. Not enough to lose sleep over.

Hope this helps.


Candango's picture

David,  Yours was a great calculation, direct and easy to follow, (even in cubic inches).



hydestone's picture

Ok, let's take a specific example with no assumptions.


My seed starter is of an unknow hydration percentage.  Most recent feeding was 100g s + 100g f + 100g w.  Would this be roughly a 100% hydration seed starter?

So, assuming it is 100% hydration seed starter, 100g of seed starter contains 50g flour and 50g water.

I need 500g of 66% hydration seed starter for a recipe.

How do I figure out how much of the seed starter to use?  Once I determine this, I can calculate the rest...I am missing a step.

How did you come up seed starter accounting for 25% of total flour?

If I was using 80g of seed starter then I would have 40g flour and 40g water.  At 66% hydration does that ean I would use the following:

80g starter (40g flour and 40g water)

252g flour

168g water

500g total weight

dmsnyder's picture


How did you come up seed starter accounting for 25% of total flour?

You will find specification of the percent pre-fermented flour a conventional way of deciding the amount of pre-ferment (of any kind) to use in a formula. 25% is a common amount. That's all.

In scaling recipes made with pre-ferments, you need to think in terms of the total dough to calculate total ingredients. However, the ingredients you actually weigh are for the levain and for the "final dough," which is made from the levain  and the remaining ingredients.


For your specific example:

You want to make 500 g of dough at 66% hydration with 25% of the flour pre-fermented. Your seed starter is 100% hydration. Let's also assume 2% salt.

So, your formula in baker's percentage is:


Baker's %










One way of computing ingredient amounts is to calculate the "conversion factor." This is the total dough weight divided by the total baker's %.  So, 500/168 = 2.98 is the conversion factor for this formula.

To calculate the weight of each ingredient, you multiply the baker's percentage of each ingredient by the conversion factor. For your formula, the ingredient weights for the total dough would be:

Flour 100 x 2.98 = 298 g

Water 66 x 2.98 = 196.68 g

Salt 2 x 2.98 = 5.96 g

With rounding to 2 places, this adds up to 500.64 g.

Now, the final dough consists of the levain + the additional ingredients. The levain contains 0.25 x 298 = 74.5 g of flour and an equal weight of water for a total weight of 149 g. So, to mix the final dough, you need to subtract the water and flour in the levain from the amounts of flour and water in the total dough. Thus, to mix your final dough, you would use:

Flour 298 - 74.5 = 223 g

Water 196.68 - 74.5 = 122.18 g

Salt 5.96 g

Levain 149 g

With rounding, this adds up to 500.14 g of total dough.

This may seem unduly complicated, but it becomes pretty easy to work with, once you understand the underlying concepts and have run through the calculations a few times.



hydestone's picture

Thanks for the thorough explanations guys, I've got it.

What is the typical range for fermented flour?  15% to 35%?  I am sure there are many variables.


Are there any rules of thumb?