What flours do you use and where do they come from?
The predominant flour is King Arthur Unbleached All-Purpose White. At around 11.7% protein it provides a pleasant chewiness and the gluten development is very predictable. KAF grains are usually grown and milled in the mid-western US where the different varieties are blended together to produce a uniform and consistent product.
For our minor flours, namely spelt and rye, we purchase organic whole grain berries from different distributors and mill our own. Using sieving screens of different sizes we mill to fine, high-extraction and whole grain standards. The grains are grown in the US. Spelt adds a mild nutty flavor, a creaminess to the color, and at around 14.5% protein increases the chewiness. Rye, on the other hand, adds it own unique flavor components but at around 10% protein it does not provide much structure.
What is sourdough?
Commercial bakers use fast-acting yeast that cause fast fermentation, so that they can produce a lot of bread loaves on a daily schedule. Fast fermentation turns starches into sugars and those sugars are responsible for the quick browning (caramelization) that you see. Check the label and you will likely see that sugars are also added to the mix.
Artisan breads are developed through slow fermentation - sometimes over days instead of hours. This slow fermentation also converts starches into sugars but then goes a step further, turning the sugars into volatile alcohols, acids, other flavoring agents and carbon dioxide. These byproducts provide the unique flavors found in artisan breads, and the carbon dioxide slowly produces the open crumb (bubbles) that so many bread lovers desire. Since the sugars are converted into other compounds they are no longer available for caramelization.
Our bread will brown when toasted but it takes a bit longer.
When I make toast, why does it take so long for your bread to brown?
If bakers didn't use leavening agents all bread would be flat. Some breads are leavened predominantly with yeast and other breads are leavened with what is called a sourdough starter. Yeast is a fungi and most baker's yeasts are highly-refined. Very specific strains are developed into the yeasts we now commonly find on our grocery store shelves.
Sourdough is another way of creating a leavening agent. Simply speaking flour and water are mixed together to create a wet paste, then set aside in a warm space to encourage bacterial and fungal growth. Over a period of days this "starter" is divided, some is tossed out, and the remainder is fed again with water and flour. On about day 3 a full-blown war begins to rage in the starter jar and if everything goes as planned, very specific strains of lactobacillus (LAB) and yeast win out. This becomes the "mother" from which small samples are used to make a levain. The levain is used as a leavening agent instead of commercial yeast. The mother is refreshed from time to time, depending on how rapidly it is depleted.
A starter's ratio of LAB to yeast is about 100:1 and the LAB convert the sugars in the flour into volatile alcohols, other flavoring agents and a little bit of carbon dioxide gas. A byproduct of the LAB's digestion of the sugars is acid which gives the bread its sour flavor, and seasoned bakers know how to coax more or less acid from the LAB using time and temperature variations. So as not to ignore the yeast in the starter they too are responsible for flavoring agents and a lot of carbon dioxide gas. It's a win - win for everyone in this process, especially those who enjoy traditional sourdough breads.