David Lohrentz and his colleagues at Madison Sourdough spend an uncommon amount of time ruminating deeply about bread.

Bread is part of the wallpaper of most people’s diet that gets tossed into the grocery basket without a second thought. But for Lohrentz, who has co-owned Madison Sourdough with head baker Andrew Hutchison since 2009, the age-old combination of flour, water and yeast is both a subject of fascination and an agent for change.

While Madison Sourdough is well-established in grocery stores, restaurants and its Williamson Street cafe (open since 2010), Lohrentz and Hutchison are anything but complacent.

They’ve switched up the selection of breads they offer for sale at grocery stores all over Madison this month, eliminating an old standard and introducing some new loaves that incorporate a larger variety of grains.

Grocery stores that carry MSCo breads include Whole Foods, Willy Street Co-op East and West, Regent Market Co-op, Metcalfe's Market at Hilldale and the Jenifer Street Market.

For some time after the duo took over operation of Madison Sourdough from its founder, Cameron Ramsay, they maintained the original bread menu.

"We pretty much left things as they were for the first six months or so," said Lohrentz. "Then we started adding some new things and subtracting a few things, but the breads that we were sending to the area grocery stores have pretty much stayed the same."

The four grocery-store loaves available were a white, a wheat, a country and a sourdough baguette.

But Lohrentz and Hutchison noticed that their Farmer’s Market and café customers were both receptive of and excited by the wider selection of breads they were experimenting with.

"Our sales of the white and wheat were kind of dwindling at the same time all this other new stuff was really skyrocketing for us, "Lohrentz said. 

Now, Madison Sourdough has increased the grocery-store bread roster from four to five, eliminated the old white and wheat sandwich loaves and added new varieties that incorporate seeds, nuts, and low-gluten grains. 

The new lineup will still include country hearth and sourdough baguettes, as well as Poppyseed Millet, a seed and grain boule, and a rotating specialty loaf.

In place of the old sandwich loaves is the MSCo Sourdough, which Lohrentz described as "kind of in between where the white and the wheat were in the past.

"It’s not as wheaty as a normal wheat bread, but it’s grainier than a white bread."

Lohrentz feels passionate about expanding Madisonians’ concept of sourdough beyond the white-flour variety.

"Sourdough can be a super-grainy dense rye, or it can be a 100 percent whole wheat, or it can be a flavored loaf like our Pepitas Polenta. It’s all sourdough," he said. "There’s no commercial yeast in this bread."

That Pepitas Polenta, one of the specialty loaves that will rotate, contains pumpkin seeds, polenta and fresh sage with whole wheat from Lone Rock’s Lonesome Stone Mill, near Spring Green.

"It’s terrific toasted and dipped in olive oil or just made into toast in the morning," Lohrentz said.

Another new addition, Poppyseed Millet is soft in the middle, made from an ancient grain that contains no gluten. 

"It gives you a little bit of texture and flavor, and a lot of nutrition," Lohrentz said.

The eight ounce Seed and Grain Demi-Boule, shaped like a squashed ball, is the first smaller-sized bread Madison Sourdough has offered in grocery stores, made with flax, sesame and sunflower seeds.

Meanwhile, the Madison Sourdough café continues to serve as a laboratory for new breads and bread-based dishes.

Any of the sandwiches there can be made with the new breads for customers who want to sample, but the menu itself contains food-geek treats like a braised beef-cheek sandwich made with meltingly tender morsels of meat in a tomato-based stew ($10.00) and a breakfast "farrato" — like a risotto — made with spelt, bacon and eggs ($9.25).

Both the new breads and the café menu are part of Madison Sourdough’s determination not to rest on its culinary laurels and to keep innovating.

"We almost pull people along," said Lohrentz. "Try this other stuff, because we think it’s pretty cool."