Sourdough - A Primer

What’s sourdough?

Sourdough bread is bread that has been leavened by a wild yeast and lactobacilli culture (typically referred to as a starter). It has a mild sour taste that isn’t typically present in bread leavened using baker’s yeast due to the lactic acid created by the lactobacilli. The lactic acid also improves it’s ability to keep for longer periods of time.

I’ve been baking sourdough for a while, but only recently started getting more into the science and art of it. There are some basic concepts that’ll be useful to know before I dive into the recipes.

All of my sourdough recipes will be in grams - sourdough (and breads in general) are fairly sensitive to changes in ratios, and so measuring ingredients by weight instead of by volume makes everything more consistent. These can be converted to ounces, but I would not recommend converting to volume.

This’ll be a bit of a long one, so here we go:

Temperature

When you decrease the temperature, the activity of yeast and bacteria slows down. This is sometimes referred to as retarding the dough or yeast. Commercial kitchens have specialty made dough retarders that hold the dough at 40 degrees Fareignheit, but the same thing can be accomplished by putting the dough in the fridge.

Conversly, increasing the temperature can increase the activity of the yeast, however the general consensus is that a long, slow rise is better for flavor development than a quick, hot rise. I’ve also heard that with a longer rise time, the yeast will break down the gluten proteins more, however I have not researched this at all.

Some general guidelines:

  • Below -4F, yeast cannot ferment
  • Between -4F and 68F, growth rate of yeast is significantly reduced
  • Between 68F and 81F, most favorable range for yeast to multiply
    • ~79F is the optimum temperature for multiplication
  • Between 81F and 104F, optimum fermentation range
    • ~95 is the optimum fermentation temperature
  • Above 104F, fermentation is significantly reduced
  • Above 140F, yeast cells die

Hydration

The hydration level of a dough is simply the weight of water divided by the weight of flour. When calculating the hydration level, don’t forget about the water and flour in your starter. For example, a dough with 500g flour, 160g starter (at 100% hydration), and 325g water has a hydration of (80 + 325) / (500 + 80) = ~70%.

Higher hydration doughs will be harder to shape, but generally have a more open crumb. Anything above 80% is very difficult to shape. I try to stay in the 70-76% range as I like how they come out, but you can modify any recipe to see what happens by increasing or decreasing the amount of water.

Flour

This is an extremely simplified explanation, so take it for what it’s worth. There are tons of different types of flours, even the same type of flour can differ between brands. For bread, we mainly care about the protein content. Some brands will actually give a number (for instance, King Arthur Flour advertises the protein content of most of their flours). In the US, all purpose flour is generally in the 9-12% range for protein; bread flour, durum flour, whole wheat flour, and semolina flours are in the 12-15%; pastry flour is in the 8-9% range, and cake flour is in the 7-8% range. Higher protein content generally allows more/stronger gluten to form.

All purpose flour will work, but is less than ideal. I usually use all purpose to feed my starter.

Bread flour, whole wheat, white whole wheat, etc. all work well for breads in terms of protein content. Different ratios of these flours will impart different flavors on the bread.

Rye flour is a very low protein flour (~7-8%), and so it is very difficult to make a 100% rye bread. However, it can easily be mixed with other flours to impart a bit of that rye flavor without going full rye.

Water

I don’t have experience with hard vs. soft water - it hasn’t been an issue anywhere I’ve lived. Use whatever water you drink - water is one of the main ingredients in bread, any off tastes will be transfered to anything you bake with it.

The only other thing to be cognizant of is your water temperature. It should be warmer than room temperature, but not hot. I haven’t measured the temperature of the water I use yet as I always just go by feel for this; but I think that it’s around 80-90F. Too cold and the yeast and bacteria will not be able to multiply, too warm and they will all die.

Starter

Starters are simply a mixture of flour and water which contain yeast and lactobacilli cultures. It takes about a week to make one (I’ll put instructions for doing this later), and it requires regular feeding to keep it alive.

You can keep a sourdough starter either at room temperature (~70F), or in the fridge. If you keep it at room temperature, then you’ll need to feed the starter every day. If you keep it in the fridge, then you’ll need to feed about once a week. Starters are relatively hardy, and so if you miss a feeding or two just pick back up and it’ll recover.

Feeding your starter

Feeding your starter is simply adding flour and water to give the yeast and bacteria nutrients. You want to add enough so that the yeast doesn’t consume all of the nutrients before the next feeding, but not so much that there’s a significant amount still left over by the next feeding. A good rule of thumb is to double the weight of the starter at each feeding. You’ll also want to maintain the hydration level of the starter (typically they are at about 100% hydration). This means that if you have 100g of starter, then you’ll want to add 50g water and 50g flour.

Keeping the size under control

Now if you keep following this advice and doing nothing else, then your starter will experience exponential growth. Let’s say you start with 100g of starter, then you’d have over 1.5 kilos of starter after just 4 feedings. Within 6 feedings, you’d need to add an entire 5lb bag of flour to keep up with it. That’s not realistic for a home baker.

That’s where discard comes in - each time you feed the starter you discard any excess before adding in the flour and water. You have two choices for this discard - either throw it away, or bake something with it. I personally hate throwing away discard as it’s a complete waste of flour.

No one has done a ton of research (or at least they haven’t posted online anywhere I’ve been able to find) about how small a starter you can safely keep. The one article I’ve found about this recommends maintaining 2oz (~50-60g) starters. I try to keep my starter around the right size where 2 feedings will bulk it up to the correct size for my recipes. That way I don’t have to waste any of my starter, and I keep the amount of flour somewhat under control.

My feeding schedule

I currently only have a single starter that I keep mostly in the fridge, and I bake bread about once a week. I try to take my starter out a day or two before I plan on making bread (so Thursday or Friday) to increase it’s activity back to normal levels. I feed it on that day, then on the next day, and finally use it and put it back in the fridge the following day. If I don’t remember to take it out a day or two early, I’ll take it out in the morning; feed it; and wait until the afternoon to use it.

Taking it out a couple days early definitely improves the result; but it’s not required.

Salt

Finally salt - it’s gotten a bad reputation recently; however it’s absolutely essential to bread making. Salt helps to enhance the flavors in your bread; without it your bread will be somewhat bland. You can reduce the quantity; however I wouldn’t recommend removing it entirely. However each of us has different dietary needs/restrictions so do what you will ;-).

Kneading

The purpose of kneading is to develop gluten in the dough. Typically recipes will tell you to knead for X minutes, or similar; however everyone kneads differently. A good way to tell if the dough is ready is the window pane test. At some point I’ll find some YouTube videos and post a link, but the basic idea is to take some dough and try to stretch it out as thing as possible - if you can get it thin enough to see shadows through (kind of like a window pane), then the dough is ready. If it breaks, then the dough needs more kneading. After a while you’ll start to figure out how long it takes for you to finish kneading.

If you google around you’ll find tons of recommendations for kneading techniques, find one that works best for you and go for it. My favorite technique is the lazy persons approach. It takes a bit longer, but requires much less effort.

Repeat these steps until the dough passes the window pane test:

  • knead for 30 seconds (focus on folding and pushing the dough)
  • rest the dough for 10 minutes

My favorite part about this is that you can even do the 30 second kneadings in the bowl that the dough is resting in (as long as it’s large enough). It usually takes 3-4 rounds until the dough is ready for me, which is much longer than the 10 minutes of constant kneading; but I can be doing other things while I’m waiting.

Resist the urge to add more flour

Most of these recipes are very high hydration doughs, which lead to a much more open crumb. If you add flour, the dough will happily accept it and keep absorbing it. The more flour you add, the denser the bread will become.

If your dough starts sticking to your work surface, then use a bench scraper or dough scraper to clear it off.

Useful tools

These are useful tools for making sourdough bread. You can certainly achieve success without them; but they’re helpful. They’re ordered by what I feel is from what I’d consider essential to what I’d consider nice to haves.

  • large mixing bowl
  • kitchen scale
  • pizza stone
  • cast iron pan
  • digital instant read thermometer
  • bowl scraper
  • bench knife
  • proofing baskets
  • lame (pronounced lahm)

Mixing bowls and a kitchen scale are extremely useful, and allow you to more accurately measure out the ingredients for your breads (and other recipes). They aren’t very expensive and make your life significantly easier.

I bake my bread on a pre warmed pizza stone and use the cast iron to generate steam in my oven. I have heard that you can use a dutch oven instead of the pizza stone and cast iron, but I have not played around with that yet.

The next couple of items are in the same family; and instant read thermometer takes all of the guesswork out of determining if bread is finished cooking, and bowl scrapers and bench knives make turning dough out and scraping down your work surface much easier.

The purpose of proofing baskets is to give the bread something to rise and still keep its shape. Anything of the right shape will work for this - just line it with a kitchen towl and dust it with flour.

A lame is used to score the loaf. It uses a razor blade instead of a knife, and goes through the dough more cleanly than most knives do; however the same effect can be achieved using a knife. Additionally, scoring the loaves is purely for aesthetics.