52 Loaves (9 page)

He sent colorful letters in layman’s language describing his observations of these sightless, wriggling microbes, “the most wretched creatures that I have ever seen,” to the Royal Society of London for the Improvement of Natural Knowledge (more commonly called simply the Royal Society), which is like my sending doodles of my garden to
Scientific American.
One can imagine the initial reception his letters must have received: a Dutch cloth merchant telling the London intelligentsia that he had discovered microorganisms and
bacteria under a microscope he made in his kitchen. Leeuwenhoek might have vanished into obscurity had not Hooke, after initially failing to substantiate the draper’s wild claims of microscopic life, gone back and built a better microscope, thus becoming the second man in history to view microorganisms.

Eventually, Leeuwenhoek got around to looking at a little brewer’s yeast under his microscope.
*
He described seeing clusters of “globules,” as he called them, and went so far as to make a wax model to play with. He squished it with his hands, tugged it, and twisted it, trying to understand the meaning and purpose behind the structure. His letter to the Royal Academy describing his findings included these sketches:

Most likely, Leeuwenhoek’s globules were yeast cells in the process of “budding.” Yeast reproduces asexually by growing a small bud that forms into a new yeast organism before breaking off, the process of cell division called mitosis.

I figured I should be able to easily observe yeast cells in the act, and I wondered if I would see anything close to what Leeuwenhoek drew three hundred years before. With the microscope set up in the kitchen, I smeared a drop of this week’s
poolish
onto a glass slide and called Katie into our impromptu kitchen laboratory. Silly me. All we could see were huge particles of flour obscuring the microscopic yeast. So we stirred about a teaspoon of instant yeast into warm water to which we’d added a pinch of sugar as a nutrient. Fift een minutes later, the mixture had turned almost creamy, frothing as small bubbles rose to the surface, and we prepared a new slide. Under the microscope, the drop of water seemed to contain a host of yeast cells, many clustered together, but at this magnification it was hard to see any detail. Yet when I moved to the highest power of the microscope, the field was too dark to see anything. I moaned to Katie.

“Let me see,” she said, nudging me out of the chair to take over the microscope just as her mother had done twenty years earlier. Katie reached under the microscope stage and turned a diaphragm I hadn’t seen, letting in more light and revealing the yeast. At high power now, several of the clusters looked similar to Leeuwenhoek’s sketches, but I couldn’t see anything that I could conclusively say was budding yeast. This was confusing. We should be seeing reproducing yeast in various forms of development. I kept searching across the field of view, moving the slide up, down, left, and right, and then I saw what I was looking for: budding yeast.

There was, however, surprisingly little of this budding going on. We prepared a few more slides but still couldn’t find much evidence. This bothered me. Had I overestimated the amount of reproduction taking place? But if the yeast wasn’t reproducing all that much, then where did all the gas that makes the dough swell come from? Just that tiny bit of yeast originally added? And I had another question: Carbon dioxide is odorless, but there were some strong, pungent smells coming out of that bubbling yeast. I wondered exactly what was going on in there.

As did Leeuwenhoek. Aside from the budding, something else puzzled him: “I saw a great number of gaseous bubbles rising from a blackish particle which was a thousand times smaller than a grain of sand,” he wrote, “but in spite of all my pains I was unable to arrive at their cause.”

In fact, it would be nearly two centuries before anyone would “arrive at their cause,” and it would happen almost by accident. In 1854 a young chemist named Louis Pasteur took a position at the new Faculty of Sciences in Lille, in northern France. This industrial city, home to a number of sugar beet distilleries, had recently underwritten the school in hopes of training its young men in practical industrial applications of science. Pasteur, though, seemed ill suited for that role, needing to be reminded by his dean to make sure his “applications adapt themselves to the real needs of the country.”

Pasteur griped about this privately but descended from his ivory tower long enough to help the father of one of his students, a distiller who was having a problem. A number of M. Bigo’s sugar beet vats were sick; rather than fermenting into alcohol, they were going sour. When Pasteur examined the contents of the healthy vats under his microscope, he saw, as expected, many yeast cells. But in the sick vats, the yeast was being crowded out
by something else—microorganisms far smaller than yeast cells and shaped like long rods.

Bacteria.

Chance favors the prepared mind.
—Louis Pasteur

Louis Pasteur claimed credit for being the first person to observe bacteria, but this life form had in fact been observed and described in some detail by that draper from Delft two hundred years earlier. Pasteur, equipped with knowledge and tools that Leeuwenhoek could only dream of, set about understanding the chemistry and biology of what was happening in both the sick and the healthy yeasty vats. One of his contemporaries, the famous German scientist Justus von Liebig, had for years loudly insisted that it was chemical decomposition of the yeast cells, not a living process, that was responsible for the bubbles in beer and dough and for the change that yeast brought to beer and wine. How could it be otherwise? Everyone knew that life required oxygen and could not possibly exist in the bottom of a beer vat.

Pasteur, however, didn’t “know.” Instead, he performed experiments in the laboratory, proving beyond a doubt that the
bubbles in the vats and the dough—the bubbles Leeuwenhoek had seen—were due to a living process:
Yeast, in the absence of oxygen, converts sugar into alcohol and carbon dioxide.
As for the bacteria, it was also feeding on the sugar but producing lactic acid, not alcohol, causing the vats to sour.

We have no record of what became of M. Bigo’s distillery business, but today, lesaffre, the largest yeast producer in the world, has a state-of-the-art plant in Lille, where sugar beets still go to be fermented. As for Pasteur, he was off and running on a career in practical science. He would continue to study bacteria and, after proving conclusively that microorganisms were not created through spontaneous generation (a fact Leeuwenhoek had pretty much established), go on to save the French silkworm industry, return to studying yeast in a patriotic mission to make French beer the equal of German (most would say he failed), and develop vaccinations for smallpox and rabies. Not to mention that, finally, Pasteur had discovered the secret of what makes bread rise, this action called fermentation, which he defined simply as “la vie sans air”—life without air—living yeast cells feeding on sugar and producing, as waste products, carbon dioxide and alcohol. Chemically speaking,

How simple and elegant. Notice how all the numbers add up on both sides of the equation, those six carbon, twelve hydrogen, and six oxygen atoms of a molecule of sugar rearranging almost in a divine plan to form two new, quite different substances.

This formula explained more than what makes dough rise. That pungent smell I’d detected in my fermenting
poolish
? Alcohol. But the left side of the equation still bothered me. Sugar is
obviously present in a vat of sugar beets, but where was the sugar in the dough coming from? My bread contained only flour, yeast, water, and salt.

I found the answer in “my Pyler,” as I’d started calling my two-volume reference book. Some of the starch granules in flour are inevitably damaged in the milling process. And it so happens that flour contains enzymes that, in the presence of water, convert these “broken” starch granules into the sugars glucose, fructose, and maltose. Not much of the flour is damaged (maybe 5 percent on average), but it’s enough to feed the yeast and to fuel fermentation, aided by a tiny amount of malt flour that is added at the mill to each bag.

What wonderful choreography of nature and man. Subtract any one dancer—the miller, for example, whose mill inadvertently damages the starch—and the ballet falls apart. Aesthetics aside, I felt I now had the full picture of what was happening with my bread. It wasn’t just rising; it was literally
fermenting
on the countertop, like wine and beer. Quite literally, in fact. A fully fermented
poolish
has an alcohol content of 3 percent—nearly the equivalent of a bottle of light beer.

Could understanding this process be key to baking exceptional bread? Surely fermentation must be as important to bread as it is to its alcoholic cousins, beer and wine. At dinner, eating another unsatisfactory loaf of peasant bread (made with a
poolish
that I’d fermented overnight, hoping to extract more flavor), I mentioned that I needed to know more about yeast.

“But why?” Katie asked. “How is this going to help you make the perfect loaf ?”

“You never know where basic science is going to lead. Look at Pasteur.” I pushed the gallon jug of milk across the table. “Read the label.”

“Pasteurized.”

After dinner, surprised at how little of the bread we’d eaten, I put the remainder of the loaf in the refrigerator, since it looked as if it was going to be around for a while.

The metric system is the tool of the devil! My car gets forty rods to the hogshead, and that’s the way I like it!
—
Grandpa Simpson,
The Simpsons

Water: 1 lb. 9.6 oz.
Salt: 0.3 oz.

I looked from the recipe to my digital kitchen scale and back again. The scale had two modes: imperial, which displayed pounds and ounces in increments of one-eighth of an ounce; and metric, which was calibrated to the nearest gram. But 0.3 ounces salt? How many eighths was that? I started scribbling on paper . . . ¼ was 0.25 . . . too little . . . and ⅜ was . . . let’s see . . . 3 divided by 8 . . . 30 divided by 8 is 3, leaving 60 divided by 8 . . .