The Fresh Loaf

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How to calculate hydration %

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Tam1024's picture

How to calculate hydration %

How do I figure out what the hydration % is of my starter.  This is what I do.  To 1/4 c. of active starter, I add 1/2 c. of water and 1 c. of bread flour.    If I wanted to have a starter at 100% hydration, how would I adjust my feeding?

dmsnyder's picture

Hi, Tam1024. 

Baker's percentages are always calculated according to the weight of ingredients, not volume. Volume of dry ingredients, in particular, is much less precise. In making your calculations, the flour is always 100%. So, a 100% hydration starter (or dough) would have the same weight of water as of flour.  

 A 100% hydration starter is generally like a medium-thick batter, depending on the flour you use and how much water it absorbs. 


susanfnp's picture

Hi Tam,

Hydration is ratio of water to flour by weight, so it's harder to calculate if you measure by volume. But assuming a cup of your flour weighs around 130 g, and water is 227 g per cup, your hydration at current feeding amounts is around 87%. (113.5 g water / 130 g flour).

To get to 100% hydration, just start feeding with equal weights of flour and water. Assuming weight of flour as above, you can do this by keeping everything the same except adding an additional 17 g or so of water at each feeding. This is about 3.5 teaspoons. Because you're starting with lower than 100% hydration starter it will not be 100% hydration right away but will settle out to this over a few feedings.


sphealey's picture

Over a moderate period of time - say, 5 feedings - the hydration percent of the starter will be the hydration percent of what you feed it with. So we can ignore the seed starter and just look at the feed.

I will use Rose Levy's chart which puts 1 cup of bread flour at ~150 g. If you find that a different chart is more consistent for you change the 150 number.

1/2 cup of water = 238 g/2 = 119 g

1 cup of bread flour = 150 g

Hydration percent = (water / flour) * 100

= (119/150) * 100

= 79.33

Say 80%.

To convert to a 100% hydration starter, begin feeding with a 100% hydration mix:

150 g flour = 1 cup

150 g water = .63 cup = 5 oz

and in a week or two if you make the charts... oops, wrong theme. In a week or two your starter will be 100% hydration.

Even if you prefer to bake by feel and cups, managing starters is one place where it is much easier and better to use a digital scale.


Yumarama's picture

Because the term "cup" is not standard across the board, nor is how well packed is is even remotely predictable, grams are the way to go. And considering that board members here aren't all American, a cup's volume capacity, transfered to ml (a more precise and universal volume measure) shows a remarkable difference:

USA: 236.6ml
FDA*: 240ml
Australia: 250ml
UK: 285ml
(* Food and Drug Admin. <-- even in the US, you have two conflicting measures)

As you see, there's up to almost 50ml differences in official "cup" measures or about 20%. So even with something as supposedly "standard" as "a cup of water", there will be different amounts. If your dough has 20% more water, even if you added "a cup" as per your local standard, that's going to throw off any attempts at getting an accurate hydration percentage; 80% or 120% hydration is not 100%, obviously. This also means that how many grams per cup you should have will differ based on what size cup you're talking about and who you listen to as to what is standard even for the same cup. My Canadian flour bag/manufacturers (Duncan Hines Whole Wheat, Robin Hood Bread, President's Choice UAP, Oak Manor Organic Rye) all tell me that a cup is 120g but as stated above, Rose Levi says it's 150g. Same North American cup size here, different weights.

Then there's the inconsistency of how much flour you're scooping in that cup: is it packed or fluffy? Ask ten people to scoop a cup and weigh it, you'll get ten different weights. Ask them to scoop five of them, you'll get 50 different weights. If you were to weigh a few of your own scoop, you'd likely find a change in the numbers from scoop to scoop. However, if you weight 120g of flour, it doesn't matter how you scoop. Adding 12, 83 or 271g of water to 12, 83 or 271g of flour will always be 100% hydration, whether that's a spoon, a cup, a can or a shoe-full.

Now that it's past it's starting stage, my starter gets regular feedings of:

30g of old starter, 60g of water and 60g of flour.

This gives me a total of 150g starter or approximately a half cup of starter once all mixed up. This fits nicely in a half litre (half quart) mason jar with plenty of room for it to expand while not using up too much counter or fridge space or needing larger amounts of flour that just gets tossed at each feeding.


gnowetan's picture

this helps immensely.  I've been reading everywhere about hydration levels and didn't quite know how to calculate.  I even came across a recipe that called for 116%!  I guess that means 1.16:1 ratio water:flour, correct? 

How many times do you have to feed it at a particular ratio to make sure that you get your target hydration (or is it more of a "ballpark" kind of deal)?

-Nate (