## Converting starter hydrations: A Tutorial. Or through thick and thin and vice versa

Questions regarding how to convert one kind of starter into another are frequently asked on The Fresh Loaf. The easy answer is to just take "a little bit" of seed starter and add enough flour and water to make a mixture of the desired thickness. This is fine and it generally works very well. However, sometimes a recipe calls for a precise hydration level levain and changing this, even a few percentage points, will make the dough consistency quite different from that intended by the formula's author. For those times, one needs to be more precise in making up the levain.

To convert a starter of one hydration to a starter of another hydration - *For example*, if you have a 50% hydration starter and want to build a 100% hydration starter from it.

Here's a general method for a precise conversion:

**First**, you need to know four things:

1. What is the hydration of your seed starter?

2. What is the hydration of your final starter?

3. How much of the total flour in your final starter comes from your seed starter?

4. How much (weight) final starter will you be making?

**Second**, you need to calculate the total amount of flour and the total amount of water in your final starter.

**Third**, you need to calculate the amount of flour and the amount of water in the seed starter.

**Fourth**, you can now calculate the ingredients of your final starter. They will be:

1. Seed starter

2. Flour (from seed starter plus additional)

3. Water (from seed starter plus additional)

So, let's see how this method works with some specific assumptions.

*The four things you need to know:*

Assume you have a **50% hydration seed starter** that you want to use. Assume you want** to make 100 g** of a **100% hydration starter**. And assume you want **the seed starter to provide 25% of the total flour in the final starter**.

Note: Using "Baker's Math," Flour is always 100%, and all other ingredients are proportionate to the flour. So, in a 50% hydration mix, the water is 50% (of the flour, by weight). If hydration is 125%, the water is 125% (or 1.25 times) the flour.

*To calculate the total amount of flour and water in your final starter**:*

Flour (100 parts) + Water (100 parts) = 100 g

So, the 100 g of starter is made up of 200 "parts." The weight of each part is calculated by dividing the total weight by the number of parts. So, 100 g /200 parts = 0.50 g. This number is sometimes called "the conversion factor."

Then, since there are 100 parts of flour, its weight is 100 parts x 0.5 g = 50 g.

The total water in the final dough is 100 parts x 0.5 g = 50 g.

*To calculate how much flour will come from the seed starter and how much will be added to make the final starter:*

We now know that the total flour in the final starter will be 50 g. But we decided that 25% of this flour is going to come from the seed starter. This means that the seed starter must contain 50 g x 0.25 = 12.5 g of flour, and the flour added to this to make the final starter will be 50 g - 12.5 g = 37.5 g.

*To calculate the total weight of the seed starter and the weight of water in the seed starter:*

We now need to calculate how much seed starter it takes to provide 12.5 g of flour, and how much water is in this amount of seed starter.

If the seed starter is 50% hydration, it contains 100 parts of flour and 50 parts of water. We know then that the amount of water is 50 parts water/100 parts flour = 0.5 parts of the flour. Since we already know that the flour has to weigh 12.5 g, then the water must weigh 12.5 x 0.5 = 6.25 g and the total weight of the seed starter is the sum of the water and flour or 12.5 g of flour + 6.25 g of water = 18.75 g.

*To calculate the weight of water that must be added to the seed starter to make the final starter:*

Now we can calculate how much water must be added to the seed starter to make the final starter. It is the total water in the final starter minus the water in the seed starter or 50 g - 6.25 g = 43.75 g.

Now we know "everything!" To make 100 g of 100% hydration starter, beginning with a 50% hydration seed starter, we would mix:

1. 18.75 g Seed Starter.

2. 37.5 g Flour

3. 43. 75 g water

This method can be used to build any amount of starter of any hydration using a seed starter of any (known) hydration.

David

## Comments

To Evangelical Carbotarianism.

David, I expect someday soon to be precise enough with Sourdough hydration percentages to find this tutorial extremely useful.

Glenn

David,

I liked this, but realize some people don't like doing the math.

If one prefers a spreadsheet this might help. First is a picture of the spreadsheet with David's example. After that is the text from a .csv file that seemed to work for me when opened with openoffice. (Formatting is lost, but easily added by hand and then save file in a .xls or .ods format).

Note that I added an extra column to show the formulas used in Column B. Let me know if you have problems with the csv file.

One other thing to note is that the weights can be any units as long as they are all the same!

Here is text from csv file, highlight all the lines and the copy and paste this into a .csv text file on your computer, then open it (double-click for many), then "save as" a spreadsheet.

"First, you need to know four things: ",,,"Formula"

"hydration of your seed starter? ",50,"%","<user enters>"

"hydration of your final starter? ",100,"%","<user enters>"

"How much (%) of the total flour in your final starter comes from your seed starter? ",25,"%","<user enters>"

"How much (weight) final starter will you be making?",100,,"<user enters>"

,,,

"Second, calculate the total amount of flour and the total amount of water in your final starter.",,,

"Flour (weight)","=B5*100/(100+B3)",,"'=B5*100/(100+B3)"

"Water (weight)","=B5*B3/(100+B3)",,"'=B5*B3/(100+B3)"

,,,

"Third, calculate the amount of flour and the amount of water in the seed starter.",,,

"Flour from seed starter","=B8*(B4/100)",,"'=B8*(B4/100)"

"Weight of water in seed starter","=B12*(B2/100)",,"'=B12*(B2/100)"

,,,

"Fourth, calculate the ingredients of your final starter. They will be:",,,

"1. Seed starter","=B12+B13",,"'=B12+B13"

"2. Flour to be added","=B8-B12",,"'=B8-B12"

"3. Weight of water to be added","=B9-B13",,"'=B9-B13"

"Total weight of final starter","=SUM(B16:B18)",,"'=SUM(B16:B18)"

Let me know if you find any errors, wayne

That was my project for this evening! You beat me to it! :-)

I like the way you formatted the spreadsheet.

David

There's also a nice one on the forum at http://northwestsourdough.com it was made posted by 'ice'.

You've got to be kidding me!

Actually, not.

David

I wonder how the French village women, not to mention those folks back in ancient Egypt, managed to bake sourdough breads in centuries past, without spreadsheets, calculators and super scales...

Quite humbling to think about, especially when you consider all the gadgets and parts of technology we "just can't do without".

With an abacus? :>)

SteveB

www.breadcetera.com

French village women were actually quite adept at solving multi-variate simultaneous equations.

However, in order not to make the village men feel threatened, they kept the secrets to themselves and passed it down to their daughters, and their daughters daughters...

No stinkin' spreadsheets required :>)

My impression is that, traditionally, the levain was preserved by saving a portion of each day's dough to leaven the next batch. Thus, the levain hydration would be the same as the final dough hydration. No calculations would be necessary.

And, I want to reiterate that the kind of precise calculation I went through is necessary only when the closest possible reproduction of a bread is the goal. It is by no means necessary to make "good" bread.

David

Could there be, I wonder, a tendency among home bakers - the hardcore ones - towards obsessive (if not compulsive) personality traits...?

I have no choice, twere I to be completely honest about it, than to shoot my hand up as fitting this basic profile, and I venture to suggest that you, Dr David Snyder, and you, Wayne, have demonstrated in this very thread that you are not out of place under this same umbrella - no need to bother about a show of hands!

Without expanding further and pointing to evidence in previous threads that might well tar others with this obsessive brush (not mentioning any names, Hans, Sylvia or Mini), I humbly put forward this theory for due consideration...

Yours,

Ross (OB)

Speaking for myself, this methodology is just a tool, to be used when needed. My intent is to describe, not to prescribe.

David

I understand what your intent was.

Mine was a flippant remark. Although... I do think there's some support for the theory I proposed. Whatever, it's not a criticism - just an observation.

It's okay. I didn't take your comment as a criticism.

My one compulsion is to explain clearly.

David

And yes, your VERY clear VERY detailed directions on the many recipes of yours I have dutifully filed away in my kitchen 'bread' file informed my observation as much as the Excel sheet in this thread!

Maybe I shoulda used a phrase like 'meticulous attention to detail' instead of tossing off a term like 'obsessive'!

Anyway, there is a great side to obsession - it is a pre-requisite of excellence in performance, art...and top quality bread!

BTW, I have a compulsion to reply to replies!

Cheers

R

I will freely confess to a certain anal compulsivity, however, at my age, thinking things through in a computer spreadsheet is the best way I've found to remember tomorrow what I thought of today... ;-)

Ron

Great postings and nice work on both your parts, David and Wayne. At least IMHO

Ron

If I had an emulsion compulsion, it would only be because it rhymes...kinda like my discretion obsession.

Glenn

After having read the first few comments on this forum with interest in the whole conversion process, I very much enjoyed the hilarious banter at the end. You guys are better than a comedy show! Thanks for the morning cackle! : )

Yes, if you can make someone smile, that goes in the positive side of the ledger. (º¿º)

Ron

Hi David - I'm digging into this formula to convert my 100% levain into Dan Leader's "stiff dough levain" at 45%. One question: for point #3 of the First step ("How much of the total flour in your final starter comes from your seed starter?") you say:

Assume you have a

50% hydration seed starterthat you want to use. Assume you wantto make 100 gof a100% hydration starter. And assume you wantthe seed starter to provide 25% of the total flour in the final starter.My question: how do you come by the 25%? How do you determine the % of flour you want the seed starter to provide?

thanks,

Dave

Hi,

The percentage of pre-fermented flour to have in a formula is entirely your choice, but you should have a feel for how to make the decision. It is going to impact the flavor profile, the degree of sourness, dough structure, etc. That choice might be associated with choices for other variables, such as length of bulk fermentation, temperature of fermentation and whether or not to retard the dough.

22 to 25% pre-fermented flour is a common amount for mostly wheat flour breads. Many rye breads have a higher percentage of pre-fermented rye flour because of the improved digestibility and avoidance of a gummy crumb from pentosan degradation. There are negative effects as well as positive effects of pre-ferments in general (not just sourdough starters), so the conventional amounts used are those found to strike a good balance.

That's a general answer. If you want more detail, I'd suggest you read about it in a book for professional bakers such as Michel Suas'

Advanced Bread and Pastry.Happy Baking!

David

Would it also work to calculate the amount of flour/water in the x% starter on hand and the y% starter in the recipe and then adjust the flour/water used in the "main" dough accordingly (rather than building a starter to y%)? I found this thread because it seems to me this should work, but I can't quite figure it out.

Hi,

If I understand your question, your point is correct. However, the issue was the

choiceof how much flour to pre-ferment. Choices such as the proportion of pre-fermented flour and the type of pre-ferment (poolish, firm levain, pâte fermentée, etc) make a difference in dough physical characteristics and the character of the final product.David

Thanks...I was just checking that I (kind of) understand what is happening! For the moment I am converting and adding/subtracting from the rest of the flour/water because it's simpler and--at this stage in my learning and with the small amounts of starter I am using--I don't think it's a significant enough difference for me to obsess over. Yet.

Since I found myself with bonus time today (afternoon off unexpectedly) I spent the afternoon trying to understand hydration conversions. I finally get it thanks to your explanation way back when. For whatever reason the way you presented it works for me. I used to look at this 1st build, 2nd build and think "what in the world are they talking about". Now it all makes sense. With the before amount and hydration I can go to any amount and hydration. Honestly today that's pretty exciting!

Thank you for your clear and concise explanation.

Now if I could just learn to manage my time...

If you found free time and learned bakers' math, I'd say you know something about good time management!

If you can stand a bit more excitement, Baker's Math: A tutorial might also be of interest.

David

I found your tutorial on Baker's Math very early on. I didn't have trouble with that concept at all. I understood fairly easily that the %'s all relate back to the flour at 100% and everything flows from that figure.

Your tutorials are invaluable. Thank you for taking the time to share.

My next mind bending lesson will be to read/research levains and why we would choose one percentage of the flour weight over another for a levain and the impact overall. That should keep me busy for a while.