June 27, 2014 - 10:02am
Lactobacillus versus Acetobacter
Which one gives the sour flavor? I've read that less hydration in the starter produces more acetobacter giving a more sour flavor. Please keep replies short. 8) I'm very very confused with conflicting information I've been given. Would Hamelman's explanation on pg 58 of Bread, first edition, be accurate?
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Lactic: yogurty, sweet twang
Acetic: lemony vinegar sharp twang
Yes a stiffer dough/starter promotes more acetic than a liquid and vice versa. But there is always more lactic than acetic in dough. Also cooler temps tend to promote the development of acetic acid indirectly.
There is a great deal of info on this if you are interested. I suggest looking at some of Debra Wink's posts here at TFL. They seem a bit complex (which they are) but she does an excellent job of explaining it.
Josh
I thought you were referring to acetic acid. I assumed that was what you were referring too.
Josh
Forget Acetobacter. Lactobacillus produce the acetic acid found in sourdough. In a healthy SD starter acetobacter play an insignificant role. They can be found on the surface of the SD starter where oxygen is present. So if you keep a firm starter discarding the crust / skin makes sense.
you state: "So if you keep a firm starter discarding the crust / skin makes sense." Please elaborate.
If you visualise a firm starter you can see there are two consistencies. The inner pure "heart" of the dough and the outer skin / crust. So you have two different environments / habitats. The skin will allow for a different micro flora to develop. So for best results only use the heart.
Is thiis practiced? That is to discard the exposed portion of a stiff levain?
I feel like I've read this somewhere way back when but the opposite. To use just the skin. Maybe to develop a more acetic starter??? Can't recall but it's banging in my brain as I read this.
Josh
I watched a tutorial on making a stiff Starter * that was made with equal amounts of Flour and Jogurt * for the initial mix, later Flour and Water, to discard the skin and use the moist heart of it for baking and refreshing.
exactly what Michael says.. I skim off the hard crust and go for the good stuff below. I also use the hard crust too, especially at the end of an 8 week fridge retard but it isn't as vigorous or produce as sour a bread for some reason..
Lactobacillus has a very simple metabolic pathway. One glucose becomes two lactic acid, or if the lactobacillus is heterofermentive it can also make alcohol with CO2. Lactobacillus cannot make acetic acid.
I know Bob wants to put a lid on this thread, so I'll keep it short. The most common SD species is l.sanfranciscensis a hetero-fermenter which does indeed produce acetic acid along with lactic. Look it up...
The "best known" would be a by far better moniker.
Doesn't lactobacillus produce lactic acid?
Produces both kinds of acid depending on the environment. Manipulating that is a way to a tangier loaf.
Acetobacter is type of bacteria that converts ethanol to acetic acid in fairly oxygen-rich environments. It's what turns wine into vinegar. Acetic acid in starters is produced by lactic acid bacteria and has nothing to do with the former type.
It appears a lot of people are under the impression that lactobacillus or more generally lactic acid bacteria (pediococcus maybe?) create acetic acid. As a homebrewer with an interest in sour beers, I'm certain that lactobacillus does not create acetic acid and can track down sources to that effect. Pediococcus maybe makes acetic, and there are other lactic acid bacteria that I don't know very well either. However, I know for certain that both acetobacter and brettanomyces make acetic acid, and are very likely to be part of the microflora in our starters. I'm wondering where this idea that LAB and saccharomyces are responsible for everything in sourdough starter comes from, and that other genuses don't contribute.
Okay I really appreciate all of the replies and I've gone most of the way thru Hamelman's book, Bread, 1st edition. For sourdough, e best explains the production of lactic acid versus acetic acid on page 354. It's a very easy read with a few fluorishes.
Warm envt + lactobacillus ------> lactic acid
Cool envt + lactobacillus ------> acetic acid
Google "heterolactic fermentation acetic" and choose a source you deem trustworthy.