The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Firm starter acetic or lactic? Conflicting sources.

hokietoner's picture

Firm starter acetic or lactic? Conflicting sources.

I've seen several places on this forum say that a stiffer starter encourages the creation of acetic acid which causes a more sour sourdough. (particularly here:

However, in Reinhart's "Crust and Crumb" he says several times the opposite:

"[The starter] uses a firm mother rather than a sponge, which promotes the growth of the less sour lactic bacteria rather than the acetic bacteria that trive in the wetter medium..." (p79)

"What makes this a San Francisco-style bread is a sour rather than mild starter, a wet rather than firm mother sponge,..." (p76)

"The thicker sponge encourages more of the sweeter lactic acids, while still promoting sourness. As a rule, lactic acid-producing organisms prefer drier sponges and acetic acid (sour) producers like wetter, looser, more oxygen-rich sponges." (p73)

So you can see this isn't a typo as he says it many times. What do you all think?


Mini Oven's picture
Mini Oven

and yes, it is milder up to a point. That point has to do with how long I let refreshed starter ferment at room temperature. If I want it real sour, I let it ripen at room temp and give a good portion into a recipe. I also know to that to keep it mild, I drop the ripening temp or give it more food. The Sour seems to be a byproduct of the fermenting process. The faster it ferments, the more sour it seems to have.  I think liquid starters tend to ferment faster.

If my starter is a bit sluggish and it's already contributed to the flavor, and I don't want too much sour, or I can't wait to let it sit overnight in the fridge, I add some instant yeast to the dough to speed up the final rising or proof to have it in the oven within 3 hours. My starter at the moment is Rye. I'm very happy with it.

Yesterday I refreshed it, let it sit out about 8 hours room temperature then added a little more water and rye flour to that. (Set some aside and mixed in more flour for a new firm starter.) Then added more water to make a cup (pancake consistancy) for my muffin recipe. I didn't want it too sour so I popped it into the fridge overnight. It did not rise much but it was full of activity and bubbles this morning. My muffins came out wonderful (Thanks for the recipe Mike) and I'd be very surprised if MIL can figure out it's sourdough. She's muching on them now.

This same starter I use to make my very sour Rye loaves, very popular here in Austria and Germany. I then build up my starter, in steps, using different temps until most of my rye flour is thoroghly soured. This is not so tricky as it first seems. It works for me.

I don't see all the tips as conflicting because each tip is correct in its own way. The variables also vary, so do the habits of each baker. What works for one, might not, or then again may work for another. Each person needs to find what works for them. The more resources and tips available, the easier it is to figure out. There is no recipe that works for everyone, all the time, in every location, in exactly the same way.

Mini O

JERSK's picture

  I was always under the impression that the formation of acetic acid and lactic acids was more a function of temperature. I referenced RLB's Bread Bible and she states 40-55 degs. as ideal for acetic acid development and 55-90 degs for lactic acid development. I have also read this in other books. In my own personal experience. I have found that longer, cooler fermentations create a more sour flavor.

Larry Clark's picture
Larry Clark

There is a lot of conflicting advice from the experts. The San Francisco Baking Institute advises firm starters and cool temperatures for a more sour flavor. See Baker's Tips - "Trouble Shooting Your Sourdough"

Nothing I do to my starter seems to have much effect on the final result



breadnerd's picture

I was taught (a class with Didier Rosada from SFBI) that firmer = acedic = tangier, and it seems to hold true from my own experiences. As previously said there are other factors such as temperature feedings etc that affect the flavor and bacterial development.

Keep in mind too that crust and crumb was published in 1998-- as Larry said experts differ in their opinions and different research/schools of thought develop over the years I can't recall what Reinhart says in his later books--but I do know some of his other techniques have changed over the years.

Why don't you try some experiments for yourself--split your starter into two--make one firmer for several feedings and make two batches--let us know your results! :)


dmsnyder's picture

By 2001, when "The Bread Baker's Apprentice" was published, Reinhart had apparently changed his mind. See the "Grace Note" sidebar at the bottom of page 234 where he writes, "Acetic bacteria prefer the denser, less-aerated environment of the firm starter; lactic bacteria prefer the wetter sponge of the barm method." 

Perhaps the most exacting study of this issue has been done by the Germans. Although the "Detmolder 3-step method" they developed is specifically for rye breads, i think the principles apply to all sourdoughs.  

Each step is to optimize one dough component. The first step is to encourage yeast production. It uses a 150% hydration dough fermented at 78F for 5-6 hours. The second step encourages acetic acid production with a firmer (60-65% hydration) starter fermented for a long time (15-24 hours) at a cooler temperature. The third step encourages lactic acid production using a wetter (100% hydration) build at a warmer (85F) temperature for a relative short time (3-4 hours). (See Jeffrey Hamelman's "Bread," page 200.) 

Now, other protocols which vary from this will yield different results. For example, one would suppose a more hydrated dough fermented at a cool temperature would not be as sour as a firmer dough fermented for the same time at the same temperature. The balance of flavors would be different, and maybe better to your taste. Maybe not. 

Few of us exercise precise control over fermentation temperature in home baking, but, if you really want a very specific flavor profile, you must have this degree of control over hydration, time and temperature, it seems. 

That's the best information I could find on this subject. Use it at your own risk. 


Mike Avery's picture
Mike Avery

Reinhart tends to play fast and loose with established terminology. His use of barm, as quoted above, is way off base. Barm is NOT a sourdough technique. It is using the yeast collected from rapidly fermenting beer to raise bread.


In the whole grain book he talks about how a biga can be yeasted or a natural pre-ferment. ALL the other sources I have read say that a biga is made with bakers yeast. If a similar thing is made with sourdough it is called a biga naturale.


He is a great baker, and he generates lots of enthusiasam, both of which are good. However, at times I question his scholarship.  When different people use the same terms to mean different things, we begin to approach the tower of babel.


I tend to go along with SFBI, Jeff Hamelman and my own experience. Thicker starters, thicker doughs tend to promote more acetic acid formation.




foolishpoolish's picture

From my own experiences and experimentation I can't yet find a definite set of rules to apply to temperature and/or hydration.

Sometimes a long slow rise of a firmer starter at cooler  temperature will yield less sour results than that of a wetter one at room temp - for example.

Again, just from my own experience, I find that whole grain flours tend to give sourer results than white.

Also the percentage 'innoculation' seems to play a part...more than just affecting the time it takes to ferment. Since the balance of microorganisms seems to change throughout a feeding cycle of starter, I would think that the time at which you 'harvested' your mother starter for making the dough would also be important.  I've found that deliberately souring my starter can also give me a 'sweeter' 'yeastier' result....

 Well...that probably just serves to confuse the issue.  Sorry.  Wish I could offer more insight.... I'm still learning.

 I have a few ideas that I want to try out in the next few weeks to make a *less* sour starter (the 'feed a firm starter at short intervals and warm conditions' method does not seem to work as well as I hoped).