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What is the role of water chemically?

Sean P's picture
Sean P

What is the role of water chemically?

why is the ratio of water to flour always 1:1 when feeding a starter? Whether it be 1:1:1 or 1:10:10 the flour and water are always the same, why? I mean what is the function of water, chemically? I accidently added about 10% more water than flour to my refreshment and it got me thinking about this.


Mini Oven's picture
Mini Oven

Flour to water ratios vary. A one to one ratio yields a 100% hydration and is easy math, half water half flour by weight. 

When making dough involving living tools like bacteria and yeast, water not only pulls the flour into dough (so it could be capable of trapping gases) it provides a way for the living cells to migrate in the dough and replicate.  Basically, flour is their food, water is their transportation. 

A basic starter ratio often uses equal water to flour. After a little experience with this ratio, many start to experiment with wetter or firmer ratios. Anywhere from super wet with twice or more times the flour weight  (good in cool temps) to a firm starter with barely enough water to make crumbs (as in starter storage or warm conditions.)  The timing of fermentation from feeding to maturity will vary with the amount of water and temperature.

There are many old formulas for feeding starters, many using volume amounts for instance: one cup flour to one cup water. Often used because a cup, not necessarily a measuring cup, is a common household object. Much more common than a weight scale.  And a one to one formula is easy to remember.  This volume ratio will give a starter hydration of over 200% as a cup of water weighs approximately twice as much as a cup of flour. The hitch comes when making the dough with such a starter as it can yield a very wet dough.  

This difference often pops up in trouble shooting starters and dough recipes. A 200% hydration starter cannot trap gas and is pretty much a liquid. Gas rising within the starter will stir the starter so that yeast can get quickly to the food. But it cannot be judged easily by eyeballing any volume rise as the gas quickly moves to the surface and is released.  Once in a thicker mix, the increase in gasses can raise the starter somewhat. Even a 100% hydration starter with equal weights of flour and water can sometimes be too thin to trap gasses and rise.  Flours vary and dropping the water amount, more in line with a dough recipe's hydration, is a better way to judge a starter's ability to raise the dough. 

When I look at a feeding ratio, I look at the starter to flour amount first. Ratios can be written  starter,water,flour  or starter,flour,water.  Note the difference.  When a ratio is listed 1:2:3 and no reference like (s:w:f) is also mentioned, it could be read 1:2:3 or 1:3:2.  When listed 1:2:2 there is no need to mention which one is water as both water and flour are the same.  This avoids a lot of confusion.  As you gain experience with your starter, you may find yourself changing the water (and flour) amounts to suit both the starter and your schedule.  

gavinc's picture

Great answer Mini.  I can add a bit more regarding the action of water in the dough.

  • It is the presence of water that gluten forms.
  • Water serves as a solvent and dispersing agent (for salt, sugar and yeast).
  • Water is necessary for yeast fermentation and reproduction (and softer doughs will ferment more quickly than dry doughs).

I've also noted that high protein flours absorb more water. 



troglodyte's picture

I learned about sourdough in the 1970s. My uncle taught me to feed sourdough by mixing 2-1/2 cups flour with 2 cups water. You mix one cup of "seed" starter from the refrigerator and let it ferment 4 or 6 or 8 hours. When it is done fermenting, you remove one cup of "seed", put it back in the refrigerator, and use the rest to make bread. With this method, you want to make sourdough starter at least every other week, more often if desired. The starter foams and bubbles but does not rise much because the consistency is like pancake batter. I have been doing it this same way all my life.

I joined TheFreshLoaf a few months ago, and learned that my starter is 148% hydration, a very wet starter compared with most here. It was a helpful lesson.

I am not saying that this is the best way or even a good way, but I hope it helps you with an example of how someone keeps a starter with a high hydration level.


Sean P's picture
Sean P

Thanks for the detailed answers.