This page includes information I have learned since publishing Bread Science.
In the quest to make the concept of baker’s percent logical, Jarkko Laine suggested thinking of it as a bar chart instead of a pie chart. His blog post, “Math for Bakers,” is here: https://bread-magazine.com/bakers-percentage/
I find the comparison of the two plots very helpful, and have created my own poster to use when I’m teaching. A traditional percent always adds up to 100%, which is represented by a pie chart. But in a recipe, the 100 applies to the flour weight, and the other ingredients are relative to it:
Jarkko’s brother suggested that the word “fraction” is more appropriate than “percent.” I’ve been thinking that “baker’s ratio” would be most correct. However, the % symbol is what appears in recipe books, so it seems we are stuck with baker’s percent.
Many different names are used for preferments: starter, sourdough starter, levain, starter sponge, mother sponge, biga, chef, poolish, and more. The names have histories that are often unknown. For example, many people claim that “poolish” originated from Polish immigrants in France teaching the concept of using a preferment.
You will find much disagreement about the “proper” use of these terms. In the bakery where I worked, for example, we used poolish for a soupy yeasted preferment; sponge for a drier yeasted preferment; and starter for the sourdough start, so these are the terms I usually use. That said, old versions of recipes at the bakery often had the other terms! I don’t argue that one term is proper; the important thing is that you don’t assume anything when you see one term used in a recipe.
Here are some fun examples that I found online for sourdough starter:
- “Levain” is the French term for starter
- “Sourdough starter” is specific to the starters created on the West Coast of the United States
- “Starter” is the part of the mixture that you keep, and “levain” is the part that you mix up to use in your dough
- “Storage leaven” is the part you keep and “starter sponge” is the part you use
- The starter mixture changes names throughout the bread-making process!
Sourdough microorganism origin
When I first published Bread Science in 2006, there seemed to be no consensus about the origin of the microorganisms. It had long been thought that location determined the mix of microorganisms, but a newer idea was that they came from the flour used.
Way back, sourdough enthusiast Mike Avery sent me a lot of interesting information about sourdough starters. He told me about experiments with irradiated flour (in which all the microorganisms were killed) and starters made with boiling water (which would also kill off microorganisms in the flour). These mixtures had a lot of trouble becoming sourdough starters. This implies that it is the microorganisms in the flour, more than the air, that result in a sourdough culture.
These days, it’s more accepted that the microorganisms come from the flour and not the location. Francisco Migoya of Modernist Bread agreed. The Rob Dunn lab at NC State University did a citizen science project in which people around the world sent in sourdough starters, which the lab characterized. You can see the results in a map at http://robdunnlab.com/projects/sourdough/map/. My takeaway from this map is that microorganism identity and location do not correlate. I made this simplified view of the map for teaching purposes:
Another question is, if a sourdough starter’s condition changes (for example, it changes location), does its flavor change? In my book, I mention evidence on both sides of the issue.
Mike Avery (in the “yes it can change” camp) suggested that starters may change flavor when a different flour is used for feeding, and that changing flour might often happen simultaneously when the starter changes location. So, it appears that the location change causes the flavor change, but really it is the flour change. This would mean that if you buy a starter, to keep it having the flavor as what you bought, you’d need to keep using whatever flour has been used.
More recently, Francisco Migoya, Head Chef of Modernist Cuisine and co-author of Modernist Bread, agreed that “using the same flour to feed [an old starter] will help maintain that particular culture to some degree.” He added that, “There are other important factors that influence how a starter develops, including holding temperature, feeding schedule, proportion of flour and water, contamination from nearby sources, and fermentation technology. Consistency in all of these factors is key if you want to preserve a SCOBY [that is, a symbiotic culture of bacteria and yeast].”
Sourdough and flavor
When I teach, students often wonder how to make their sourdough bread more or less sour. I’ve compiled this list of ways to control sourdough flavor:
- Use a different starter—different microorganisms produce different flavors
- Bake your bread the same day it is made for a less sour flavor, the next day for a more sour flavor, or two days later for even more sourness (but it might not rise as well on the third day)
- Use less starter to make the dough rise more slowly; this results in a longer rising time (stronger flavor) before the dough needs to be shaped and baked
- Use a colder rising temperature for your starter and/or dough for a harsher, more acidic behavior (via Francisco Migoya, *see below)
- Keep your starter at a wetter consistency for a more acidic bread (via Francisco Migoya)
- Feed your starter more or less often (**maybe; see below)
*I had the opportunity to ask Francisco Migoya, Head Chef of Modernist Cuisine and co-author of Modernist Bread, about rising temperature and flavor. He explained that there are two types of lactic acid bacteria (in sourdough starters): homofermentative bacteria create lactic acid (“a mellow acidic flavor”), while heterofermentative bacteria create lactic acid and acetic acid (“a much more acidic and harsh flavor”), as well as some carbon dioxide. Warmer temperatures favor homofermentative bacteria, while colder temperatures favor heterofermentative bacteria. To find your preferred method, you could try both or a mixture.
**I did a very-not-controlled-experiment blind taste test of two loaves of sourdough. Loaf B I bought at the bakery where I used to work; they feed their starter twice every day. Loaf E (for Emily) I made at home using my own starter. This started originally came from bakery B, and I buy my flour from the same mill (although I’m not 100% sure we use the same brand—not controlled, as I said). I’ve had the starter for years and feed it only once every month. We tested pieces of the crumb to avoid the different flavors of the crust. The four testers’ opinions were completely inconsistent, but they all noted some difference. So, if you are unhappy with your starter’s flavor, you could try feeding it more or less often.
Sourdough starter storage, “lazy” starter care, and starter overfeeding
In my book, I discuss freezing starter as a way to store it. I’ve now read of starter surviving a year of being frozen.
You can also store starter by drying it. Deb Bartlett wrote to me with this information about drying sourdough starter:
“One very effective way to keep starter over the long term is to dry it: simply spread some starter over parchment paper, as thin as possible (you might need to water it down a bit) and let it dry, either on the countertop or in a very low oven or a dehydrator. When it is completely dry, break it into little pieces and store it in an airtight container in a dry place, preferably out of the light.
“When you want to get a starter going again, take about 1/2 to 3/4 of a cup of ‘chips’ and pour about 1 1/2 cups of warm water over them. Soak and stir until they dissolve. You might need to add more warm water. Once that has happened, let it sit for a few hours, then feed as usual and leave out. It might need a bit longer to get to where you want it and maybe a re-feeding, but soon your starter will be alive and bubbling. You can keep a starter for a long time in the dried form, providing it stays dry in storage so that it doesn’t go moldy.”
I’ve read other accounts of successfully storing starter with this drying method, including some trials that lasted several years.
In regards to feeding a starter less often (to save time and flour), I got into the habit of feeding mine monthly, doing a double feeding with the starter out on the counter to nurse it back to health. I was scared to try any longer, but Andrew Whitley in his book, Do Sourdough: Slow Bread for Busy Lives, describes a starter living for five years with no feeding! I can report that I have now forgotten mine for three months, and it recovered the same as usual.
And finally, I’ve had an opposite situation come up repeatedly so I want to mention it: overfeeding starter. I’ve had people tell me “I don’t know what went wrong, I fed it so much and it completely stopped working!” Each time you feed starter, you dilute the supply of microorganisms. Then you have to wait for the starter to rise, and the microorganisms to reproduce. YOU MUST WAIT UNTIL IT IS FULLY RISEN BEFORE YOU FEED IT AGAIN. These well-intentioned folks were feeding their starter before it had fully risen, then feeding it again. Essentially, they were diluting the microorganisms until they were left with a mixture of flour and water, with no microorganisms.
If you’re not sure where your starter is at in its cycle, it’s better to let your starter be over-ready. In the bakery, our starter would be ready to go at 5 AM. We would use it in various recipes throughout the day. It did just fine at 11 AM or even in the afternoon.
Gluten, kneading, and no-knead bread
For the longest time, I didn’t know how to explain no-knead bread. If kneading developed the gluten, how did no-knead bread work?
I noticed that no-knead bread recipes seemed to have a few common characteristics: a wetter dough, a series of folds, a long fermentation time, and baking in a covered dish like a Dutch oven. The wetter recipe helps molecules move about and form bonds in the dough; the folds act as a bit of kneading; and the long fermentation time gives the gluten time to develop. I’d also heard the idea that as gas forms in a dough, the gas bubbles themselves stretch the gluten, enabling its bonds to rearrange—as if the gas itself is kneading the dough. The Dutch oven, as far as I can tell, is simply included because it’s the all-around best way to bake!
But still the explanation felt incomplete.
Finally, I had it explained by Francisco Migoya (Head Chef of Modernist Cuisine and co-author of Modernist Bread). He wrote that the key to gluten development is the flour becoming hydrated (not kneading!). In a no-knead recipe, that hydration happens during the long fermentation. Kneading can speed up the process, and kneading can create a different bread texture (mainly a tighter crumb).
An additional thought that I have had is that at the scale we are all used to (human-sized objects), we think of hydration as an instantaneous thing. If you turn a garden hose on your friend, they’ll be instantly wet all over. In dough, however, hydration means water molecules working their way through a mess of gluten and starches. Positive and negative charges pull at the water, and it might bump up against another molecule and not be able to keep moving for a bit. At this smaller scale, hydration takes time.
People often ask if a convection oven is good for bread-making, or if they should use the convection setting on their oven. I’ve witnessed good and bad results from convection, so it seems like it depends on the particular oven. My worry was that the oven fans would remove moisture from the oven air. At one house, we baked with a convection oven, and the bread had a lovely brown crust. The owner said he thought the fans recirculated the oven air without replacing it. This makes sense—why would the oven fan suck out the air (and heat)? But then, at another house, the “TRU Convection” setting produced terrible crust, and the brownness and shine improved when we turned it off! Try baking with and without convection in your oven and see which is better.
Steaming dough, baking stones, and more
When steaming dough, spritzing the oven doesn’t always work because if the oven is very dry, the steam will not be enough (I imagine it simply sticking to the walls, but I’m not sure if this is true). When teaching, I’ve often observed that the first loaves baked get terrible color, but after that, things improve; my guess is that the ovens are dry to start with, but after a batch of loaves have baked, the ovens are more humid. The steaming methods that work well either produce a lot of steam, or they produce steam over time so that the oven becomes a more-humid environment before the bread enters. If you use a method involving pre-steaming with a cup of water, remember that this water removes heat from the air as it warms up; don’t use a large reservoir of water, or you’ll be hurting your bread by ruining the oven’s heat.
I now think using a covered dish is the absolute best way to bake. It always produces the best height and crust, especially with sourdough loaves that have been in a fridge overnight and may have trouble recovering. Preheating the dish is key! I have my students remove the whole dish from the oven for ease and safety. It’s hot enough that you don’t need to rush getting your dough in. Another tip is to have your dough on parchment paper, which you can lower into the dish. (Make sure the parchment can heat to 450°F, or it might stick to your bread.)
I’ve become concerned about cracking pizza stones, casseroles, and even oven windows, and urge everyone to be careful when baking! Here are some things I’ve discovered:
- Cold water dripping on a pre-heated oven window can crack it! Be careful when you place a dripping loaf of dough into the oven, or when your nervous hand reaches over the oven door to pour water (for steam) onto a hot frying pan. Some people quickly place a towel over the oven window and then whisk it away before closing the door.
- The oven light can crack if hit with a spray of water.
- Pizza stones can also crack. The instructions say to preheat the stone with the oven, not put it in cold. This is to avoid the extreme temperature changes that crack it. But putting cold dough on the hot stone can also crack it. I used mine regularly, with no problems, and then it cracked during a class when it had been in the oven all day. It was a thin pizza stone. (Mom got it from the Pampered Chef.) If you want to do heavy duty baking on a stone, I’d recommend seeking out a heavy duty stone. Another suggestion (from a reader) is to use kiln shelves. You can get them from online pottery suppliers, and they “come in all sizes, shapes, thicknesses, and strengths. The higher fire varieties are harder to break, i.e. more resistant to shock, but more expensive.”
- If you’re using a casserole avoid using anything special. The material should be Pyrex or something designed to handle temperature changes. I use old Corningware casserole dishes, and they work great. They get brown marks on them after a while. You can often find them at thrift stores. I also use an old Creuset pot, and Dutch ovens work great. If your bread sticks to the bottom, try using parchment beneath it.
Internal temperature when bread is done
On page 201 of Bread Science, I describe using an internal temperature of 180 to 200°F to indicate that bread is done baking, because around this temperature the starch solidifies. For years, this test never let me down, and it has still never failed with a home oven. The one time I experienced unbaked bread over 180°F was when a friend tried to bake a loaf in a 700°F wood-fired oven. The loaf browned quickly, so we pulled it out and took a temperature. It was over 180°F inside but still doughy when we cut it.
A talk with Francisco Migoya (Head Chef of Modernist Cuisine and co-author of Modernist Bread) explained the situation: Bread’s “doneness” depends both on temperature and moisture. Usually the two go hand in hand. In the case of the super-hot oven, the temperature rose, but not enough moisture had left the dough for it to be fully baked. Francisco suggested 195 to 200°F as a safe temperature range for enriched doughs, and 208 to 212°F for doughs like French and sourdough. He also noted that denser, wetter dough, like rye doughs or doughs with whole grains, require higher internal temperatures to avoid a gummy crumb, because more water must evaporate; they have to sit at 212°F (the boiling temperature of water) for a bit.
Also note that bakers have varying opinions on the correct temperature. I like 190°F (the average of the range given above) because I like the idea of the starch solidifying as a determination that the bread is done. Some bakers give 200°F, 210°F, or a higher temperature as the “correct” temperature for a certain kind of bread (with different temperatures appropriate for different types), stating that a specific amount of moisture loss will give the best loaf. As always, I recommend taking data and finding the method that makes the bread you like best.
Doc Dougherty alerted me to this paper that examines tyrosine cross-links in gluten as an alternative to the usually accepted disulfide bonds. Basically, they make some dough and then run it through machines to analyze its amino acids, and they see that tyrosine cross-links are present. It seems likely to me that both types of bonds, tyrosine cross-links and disulfide bonds, could be at work!