This is part 2 of a three-part series examining the flavor of sourdough bread, and how to adjust it to taste. For this all to make sense, please be sure you've read part 1 (on ensuring a healthy starter) before proceeding to this article, and then to part 3.  

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As covered in part 1, you’ve built a healthy sourdough starter, it’s been fed, and now you have an active workforce of both wild yeast and lactic acid bacteria (LAB) that’s ripe and ready to rock your bread-baking — great job!  

Because our “mother” starter has been nurtured in a way that keeps both the yeast and LAB active, we're now able to focus on flavor. Remember that when focusing on the starter culture, we have to be a little more cautious about how we tip the balance between yeast and LAB in order to keep our starter rising properly. Now we can make some choices that will encourage more LAB growth, and consequently more acid production (which is the key to developing sourness). Or, if we prefer to minimize sourness, we can aim to discourage LAB growth and limit acid concentrations.

In this article we'll examine the flavor components in a typical sourdough bread recipe, Pain au Levain, so that in the concluding article of this series we can actually make adjustments to direct the development of the bread's flavor. But first, let’s revisit those factors we talked about earlier, now focusing more fully on how they influence flavor development.

Flavor development Milder: less acid Tangier: more acid
Consistency Firmer Looser
Temperature Cooler Warmer
Ripeness Less ripe More ripe
Feeding / frequency Smaller / more frequent Larger / less frequent
Flour White Whole grain

What’s your next step? Making dough that optimizes conditions for your preferred flavor: super-sour, mild, or something in between. Higher acid concentrations can produce assertively sour bread; lower concentrations, a milder loaf. 

Sounds like a simple answer, right? But if you’ve been baking with sourdough long enough you know that nothing is truly straightforward; sourdough is a continually evolving balance of all the factors above. And there are an endless number of ways to tweak these factors to achieve different results.

It’s also important to recognize that the tanginess under discussion here is just one aspect of sourdough flavor development. There’s so much more to flavor (sugars, amino acids, acetate esters, aldehydes, etc.) that varies from starter to starter, flour to flour, and process to process, and science is still trying to figure out exactly how these elements contribute to the ultimate flavor in your sourdough bread.

Let’s look at one recipe in particular to see how everything comes together to produce the flavor in a loaf. 

Evaluating a recipe: Pain au Levain 

This naturally leavened loaf is a great example of using your starter to make bread with rich flavor and mild (rather than assertive) sourdough tang.

We realize many of you are looking for more, not less sour flavor. But by understanding how everything works in this particular recipe, you’ll be able to take your own favorite recipe and tweak it to taste. (We’ll also tell you how to increase Pain au Levain’s tanginess in part 3 of this series, so stay tuned!)  

Building a preferment Lee Clark
The preferment stage builds populations of yeast and LAB, and also provides an opportunity to begin steering these organisms toward the level of tanginess you desire.

Step 1: The preferment 

Preferment (say PRE-ferment) is kind of an "interim" starter, a portion of the flour that’s fermented prior to mixing the rest of the dough ingredients; it’s the bridge between your ripe sourdough starter and the dough it eventually leavens. Preferment is the broad term for many iterations, including biga, sponge, levain, poolish, and sourdough starter.   

Made from flour, water, and ripe sourdough starter, the preferment (aka levain) for our Pain au Levain recipe ferments overnight, building populations of yeast and LAB. The preferment is the first step in this bread’s flavor development. Let’s take a closer look at how it works. 

Consistency and flour type: The recipe calls for a stiff overnight levain made with all-purpose flour. Stiffer conditions in the preferment won’t encourage as much total acid production, but will increase the formation of acetic in proportion to lactic acid. Fewer acids = less overall sourness, but the increase in acetic acid will subtly alter our perception of the bread’s flavor.

How does this work? Acetic acid isn’t more sour than lactic acid (despite what many assume); but since it has a stronger aroma, we often perceive acetic acid as contributing increased sour flavor. In reality, there will always be much more lactic than acetic acid in your bread dough; and the bulk of your bread's “sourness” is going to come from lactic acid.

Which is not to say acetic acid doesn't play a part in flavor development. Shifting the balance of acetic acid and lactic acid can still change the flavor profile of your bread, providing more depth of flavor (if not necessarily more sourness).

Temperature of preferment: The original recipe’s preferment calls for 70°F water and an overnight rise with room temperature between 65°F and 75°F. This range will encourage milder-flavored bread, especially if we opt for the cooler end of the spectrum. Keep in mind, however, that the cooler the temperature, the longer it will take for this stiff levain to ripen.

Size of feeding: The recipe’s preferment includes a relatively small amount of starter compared to water and flour (28g:74g:149g). Ordinarily, this large meal of water and flour should lead to more LAB production — and thus to higher acid concentrations later on, which should shift the bread’s flavor toward tangy. However, in this case cooler temperatures and stiff conditions are likely to outweigh this factor.

Ripe or more ripe? Typically you want to add a perfectly ripened preferment to bread dough, one at its peak of activity. Doing so will ensure that the preferment’s yeast population has grown enough to do its primary job: raising bread. However, to encourage more sour flavor it’s OK to wait until it’s a bit farther along in the window of ripeness (just beginning to fall): adding preferment to bread dough when that preferment is slightly past its peak encourages higher concentrations of LAB (and a more sour loaf).

Conversely, if you're looking for a reduction in sourness, add your preferment to the dough when it's just at its peak of ripeness, rather than waiting until it's past it.

See how flavor is beginning to take shape in the preferment? Three of the five factors above (firm consistency, white flour, and cool temperature) favor a milder loaf. Let’s see what happens when we use that preferment to make dough. 

Hands kneading dough on a table with the aid of a bench knife. Maurizio Leo
Once salt is added to the dough, population growth slows, and metabolic activity holds sway.

Step 2: The dough 

Once the preferment is combined with the recipe’s remaining dough ingredients, the salt in the dough slows down the activity of both yeast and LAB, effectively slowing or delaying any further increase in these populations. So from this point on, it’s mainly the metabolic activity of those two components we’ll focus on: what happens when enzymes break down starch and free the sugars that yeast and LAB then turn into carbon dioxide, alcohol, and organic acids.

Adding whole grain flour: Whole grain flour, particularly whole rye flour (pumpernickel), tends to promote more sour flavor in bread for two reasons.  

First, the type of sugars available in whole rye (or whole wheat) flour encourage a shift toward acetic acid production.  

The second and more significant impact of whole grains on flavor development has to do with the fact that whole grain flours contain relatively high amounts of mineral-containing compounds, which serve as buffering agents. Thanks to these mineral compounds, higher acid concentrations are able to build before the pH finally shifts lower, restricting further acid growth. More acid means increased sour flavor.

The small amount of whole rye flour (5%) in the Pain au Levain recipe will promote flavor, while not increasing acidity too much. 

Thermometer probe placed into the center of a bowl of just-kneaded dough showing a dough temperature of 75°F. Barb Alpern
The ideal dough temperature for most breads, post-kneading, is in the 75°F to 78°F range.

Water temperature: The higher the temperature of fully kneaded dough, the more likely your resulting bread will be more (rather than less) sour. The principal way bakers can influence the temperature of fully kneaded dough is through the temperature of the water used to mix the dough. 

Our Pain au Levain recipe calls for water between 75°F and 80°F. If you're mixing your dough in a stand mixer and your kitchen is in the 70s, this will most likely lead to dough that’s quite a bit warmer than our optimum range — which may translate to an uptick in sour flavor down the road.  

If it’s not more tang you’re after, lower your water temperature to produce a cooler dough. For more on how to determine optimum dough temperature, see this post on desired dough temperature

Bread dough in a covered round brotform resting in the refrigerator. Barb Alpern
While refrigerating your loaf overnight won't guarantee more sour flavor, it does shift the balance of lactic acid and acetic acid produced, which can add more depth of flavor to your loaf.

Step 3: Refrigeration 

Many of you have been taught that refrigerating a loaf of sourdough bread for 12 to 24 hours (or even longer) before baking will increase its sour flavor.  

This may or may not happen; none of the flavor-influencing factors in sourdough baking work in a vacuum, so while refrigeration will often increase sour flavor, there are times when it may not. This is especially possible if your dough hasn’t had sufficient time to ferment at room temperature prior to refrigeration: cooler conditions can slow down LAB activity, leading to lower acid concentrations (read: less sour flavor).  

I decided to do a series of casual tests, baking half the Pain au Levain dough the same day and the other half after a 24-hour rest in the refrigerator. I performed this test several times, and while most of the time my taste-testers did identify the refrigerated loaves as more sour, in one test six out of eight tapped the unrefrigerated loaf as exhibiting stronger sour flavor. 

In addition, my work on the Baker’s Hotline allows me to speak with sourdough bakers around the country on a daily basis. More than a few of these bakers lament that refrigeration does nothing to enhance the sourness of their bread. This anecdotal evidence seems to point to the fact that refrigeration (or indeed, one factor alone) can’t guarantee a sour loaf.  

Next time: Taking charge of flavor

Now that we've examined the flavor components of a recipe as written, you may be wondering: Is there, in fact, any proactive way you can make your sourdough bread more sour?  

Well, you’ve learned how a healthy starter is the basis for all great sourdough bread; and how the flavor of that bread is shaped by a myriad of factors all along the way, from starter to preferment to dough to final loaf.  

To loaves of sourdough bread on a cooling rack, one labeled more sour, one labeled less sour. Barb Alpern
Are you looking for an extra tangy loaf, or something much milder? The next post in this series will show you what steps you can take during the dough stage to influence the flavor in your sourdough bread.

Using Pain au Levain as an example, the final post in this series will show you exactly how to make sourdough bread that meets your desired level of sourness: barely tangy, assertively sour, or anything in between. 

Read more:
How to make your sourdough bread more (or less) sour: part 1
How to make your sourdough bread more (or less) sour: part 3

Our thanks to microbiologist and sourdough scientist Debra Wink, without whose generous sharing of her knowledge and insight this article wouldn’t have been possible.  

Cover photo by Lee Clark.

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Barbara Alpern in her kitchen with loaves of sourdough bread
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About Barb Alpern

Barb began baking when she was assigned the job of baker at her co-op house in college. Whole wheat challah and granola were her specialties. This led to two years at Wildflour Bakery, a wholegrain collective bakery that existed in Ann Arbor, Michigan back in the day.   Four sons and a ma...
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