By Melissa Johnson
This past week, I experimented with making challah using various sourdough starter builds or “levains” to test the outcome, particularly from the standpoint of crust browning. When I use my sourdough starter at 100% hydration to leaven enriched dough, the color of the fully baked bread is often very pale compared with the same recipe made with yeast instead. Moreover, the dough is often floppy rather than spongy even though the ingredients are the same apart from a few grams of instant yeast versus wild yeast and bacteria. After reading years ago that browning (aka Maillard reaction) could be encouraged by using a sweet stiff levain, that is what I’ve done: the night before mixing an enriched dough, I feed some of my sourdough starter with sugar, flour, and relatively less water. Below is my research into the why of this and some side-by-side experiments. It’s worth noting that sourdough starters have diverse microbial composition, and while many people have similar pale-crust results using their starter without sugar and at 100% hydration, other people’s sourdough starter already seems to favor yeast and only needs a lower hydration feed or no change at all.
What is the role of the sugar in a sweet stiff levain?
The sugar encourages the flourishing of yeast relative to lactobacillus bacteria. The sugar puts stress on both the yeast and the bacteria, but the stress is less severe for the yeast. Therefore, the microbial population in the ripe sweet starter is skewed more toward yeast and also sugar tolerance, which is helpful if you happen to be making a sweet enriched dough. This all means that the subsequent dough fermentation should result in relatively fewer acid-producing lactobacillus bacteria in the microbial population and the dough that goes into the oven will be less acidic (all other things equal).
Why does the starter have to be stiff?
Could a sugary liquid levain also work well? Most bakers agree that a dryer starter favors yeast over bacteria and produces less sour bread, even though this contradicts what we know about aerobic and anaerobic fermentation. Dryer starter promotes aerobic fermentation and thus acetic acid production (sharp vinegar flavor), while wetter starter promotes anaerobic fermentation and thus lactic acid production (softer yogurt flavor).
How is it that people perceive bread with more acetic acid as milder in sourness?
One possible explanation for this contradiction is that the overall yeast presence is higher in dry starter, overpowering any lactic acid to acetic acid shift. I looked for an explanation for why yeast would be favored and didn’t find one. The theory I came up with is that the “extra” flour in dryer starter increases the buffering capacity of the starter, allowing the pH to stay in a yeast favoring range longer. Another possibility is in the fact that acetic acid is weaker per gram than lactic acid. More acetic acid than lactic acid would be needed to drive the pH of a solution down by the same amount.
Far less doming of the dough on the left (100% hydration sourdough levain) compared with the right (sweet stiff levain). This indicates a breakdown of gluten due to higher dough acidity. I stopped the bulk fermentation of the dough on the left earlier because of this gluten breakdown.
Why does the acidity of the dough impact the crust color?
In my research, I learned that the optimal pH for the Maillard reaction is between 6 and 10. The amino acids and sugars combine into the new aromatic brown molecules at the fastest rate in this pH range. In retrospect, this makes sense because people dip pretzel and bagel dough in boiling high pH solutions (water mixed with lye or baking soda) to make them bake up a deep caramel color. But how do we reconcile this pH preference with the fact that artisan-style sourdough breads also have low pH, likely less than 5 and yet they brown nicely? More reading yielded another optimal condition for Maillard reaction to occur: temperature between 212-266°F. Baked at or over 450°F (rather than 350°F), artisan-style sourdough crusts are exposed to higher oven heat, so they’re near that ideal temperature range sooner and often for longer.
Test Bakes
The most successful bread was #4, leavened with a stiff sweet levain built from unrefreshed cold 100% hydration starter. This bread retained its shape during the final proof, neither flattening nor bursting, and it had the best Maillard reaction.
The recipe for this challah along with a round braiding video can be found here: Sourdough Challah and the starter/levain feeding ratios for the test bakes are given at the end of this article.
From left to right:
1) 100% hydration sourdough levain, fed once, fermented to 85% expansion. This dough was clearly very acidic, losing definition in the braid from gluten degradation and showing almost no Maillard reaction.
2) 60% hydration sourdough levain, fermented to 50% expansion. This dough was significantly under-fermented (under-proofed) which caused the braid rupture. It is darker than the first bread, but not as dark as the third bread — likely because the under-proofing resulted in less conversion of starches to sugars.
3) 60% hydration sourdough levain, fermented to 85% expansion. This dough was slightly under-fermented (under-proofed) which caused the braid rupture, though not as badly as the second bread. The Maillaird reaction was better than the second bread even though the starter was the same, likely because of the greater degree of fermentation.
4) Sweet stiff levain, approx 52% hydration (the water in sugar is not included in the calc), built with cold 100% hydration starter, fermented to double / 100% expansion. This dough doubled and still felt spongy and strong. The shape didn’t burst and the Maillard reaction was robust.
Conclusion
My challah test bakes indicate that a sweet stiff levain makes a nicely browned enriched sourdough with enough gluten strength to braid and survive the final proof. The presence of sugar and the low hydration of the levain favor yeast growth over bacteria, resulting in a less acidic dough that allows more Maillard reaction to take place. The testing also showed that in a less acidic dough (#2 above), underfermenting can also reduce the Maillard reaction.
Stiff Levain Builds (60% hydration) in this experiment
First levain feed with wetter starter
100% flour
50% water
50% starter at 100% hydration
Subsequent levain feeds with 60% hydration starter
100% flour
60% water
Any starter amount at or less than the flour amount
Sweet Stiff Levain Builds (52% hydration) in this experiment
Ingredient percentages
100% flour
44% water
33% sugar
33% starter
Percentages with starter as part of the flour and water amounts
100% flour
52% water
28.5% sugar
