THIS BOOK WILL introduce you to the personal satisfaction and sense of accomplishment experienced by home bakers of traditional sourdough. If you are an experienced sourdough baker, it will guide you to the sourdoughs you seek.
Let’s start by defining what we really mean by “traditional” sourdoughs. We know the sourdough process results from the fermentation reactions of two quite different classes of microorganisms: wild yeast and beneficial bacteria. For well over five thousand years, all breads were produced by the fermentation of these two essential microorganisms acting together. The yeasts are primarily responsible for leavening and bread texture, the bacteria for the sourdough flavor. Thus the definition of “traditional” sourdough requires a “culture,” or “starter,” containing both of these organisms.
Delicious, nutritious breads of various kinds were produced for centuries by a process no one understood. Bakers believed there was “something” in dough that made it rise. They knew if they saved some old dough and added it to a new batch, the new dough would also rise. For eons, all new doughs required a bit of old dough to “start” the rising process. In villages and towns around the world, bread was the staff of life—it literally supported life. People baked it in their homes, and every town had a bakery where the people could take their dough to be baked in the baker’s oven, or buy bread from the baker himself. When people emigrated to the United States, they brought their dough starters with them. The California forty-niners and the Yukon and Alaskan miners get credit for the term “sourdoughs,” probably due to the extreme flavor of their breads (the crusty miners themselves subsequently became known as “sourdoughs”). Thus our definition of “traditional” sourdough also requires a culture with organisms that, with proper care, will survive and replicate themselves forever.
In the 1800s, Louis Pasteur looked into a microscope and saw what we now call wild yeast, discovering for the first time what really made bread dough rise. Within the next hundred years, researchers learned how to select, isolate, and grow single strains of yeast in pure cultures. They searched for and found species of Saccharomyces cerevisiae
, baker’s yeast, which leavened bread doughs with incredible speed. Then industry took bread out of the home and put it in factories that manufacture something labeled “bread,” which neither looks nor tastes like the staff of life. Breads began to be produced by mammoth machines. Sourdough starters were no longer used, small-town bakeries disappeared, people stopped baking in their homes, and the staff of life became neither delicious nor nutritious. Bakers thought the need for sourdough cultures was gone forever, but they were wrong. Baker’s yeast is totally incapable of producing sourdough flavor, and without the action of lactobacilli in concert with yeast, the quality of breads has never been the same—not even close.
Within just the last hundred years, there have been monumental changes to what we call bread, and these changes are mostly for the worse. Not only do huge baking machines now dominate the production of bread, the baking industry adds a plethora of chemicals to flour and dough to change their physical characteristics and improve their “machinability.” These include surface-active agents (surfactants) to help doughs go through machinery without sticking or tearing, other chemicals to soften the final bread texture or strengthen the dough by modifying the gluten, and a host of emulsifiers just to improve the mixing characteristics or increase shelf life. All of these additives have one thing in common: no, or very limited, nutritional value. At least one of them, potassium bromate, has been banned worldwide as a potential carcinogen.
In centralized industrial bakeries, large baking conglomerates produce packaged breads and refrigerated or frozen dough for distribution to retail stores and local bakeries. The distribution of industrial bread doughs means that even if a bread is baked fresh at a local bakery, it often still contains all the additives and chemicals included by the wholesale producers to grease its progress through the massive machinery—and none of the beneficial microflora that make bread taste like bread. And this is not only an American story: the deterioration of bread quality is a worldwide phenomenon, occurring even in the European heartlands of great bread.
In spite of these monumental changes, a small cadre of hardy souls have continued using the old-fashioned sourdough methods and today they are widely celebrated as “artisan” bakers. They have persisted in baking traditional sourdoughs, and in the past few decades, the market for their products has blossomed. Industrial bread still lumbers on, dominating the market, but it is easier now than it has been in many years to find real, old-fashioned sourdough breads—or to make them at home.
The best breads available today are being produced in the home or in artisan bakeries. But in our kitchens, the techniques are not the same as those used by the artisan bakers, or by the pioneers. Early home bakers used their starters to bake almost every day. Most of us now start with a culture that has become dormant between uses. The production capacity of the artisan baker requires masonry or special ovens and equipment beyond the scope of the individual home baker. For that reason, this book is designed specifically for and dedicated to the individual who bakes for him or herself or for a family and who deserves the thrill and joy of traditional sourdoughs.
The Birth and Life of Sourdough
It took uncounted centuries for wheat and other grains used for flour to evolve. Jarmo, in the uplands of Iraq, is one of the oldest archaeological excavations in the Middle East, dating to about 8000 BC. Here, archaeologists have identified carbonized kernels and clay imprints of plants that resemble wild and domesticated wheats. Historians believe that similar grains were established in Egypt by at least the same time, and perhaps as early as 10,000 to 15,000 BC. Rye existed in the Middle East as an unwanted weed and eventually spread across the Mediterranean to the Baltic countries, where it dominates bread making to this day. These wild grasses took millennia to progress to grain-producing plants, and it was many centuries before humans learned to cultivate and use them for food.
Grains like wheat and rye were probably first consumed as porridge. Eventually, this gruel evolved into a flat cake of baked cereal—baked perhaps on a hot rock in the fire. But how did these flat, hard cakes rise for the first time and become bread? An unbaked cake, perhaps forgotten on a warm summer evening, would be a perfect medium for contamination by an errant wild yeast. Imagine how many times that accident occurred before someone saw it and then baked it! It must have taken a thousand years, a thousand accidents, and finally a thousand experiments to produce a recognizable loaf of bread.
The Discovery of Yeast
In 1676, a Dutch lens grinder, Anton van Leeuwenhoek, first observed and described microscopic life, and in 1680, he produced the first sketches of yeast in beer. But for the next 170 years, nothing more happened to further our understanding of bread’s secrets. Then in 1857, Louis Pasteur proved that fermentation is caused by yeast, and a comprehensive system of yeast classification, which we still use, was published in 1896. With Pasteur’s work, a whole new field of yeast technology and cereal chemistry came to life. Microbiologists learned how to isolate single yeast cells and to select pure cultures. They selectively bred wild strains to develop yeast cells that leavened faster, were more tolerant to temperature change, and were easier to produce commercially. Modern mass-produced cakes of pressed yeast and packages of active dried yeast contain billions of cells that are all exactly alike. These purified strains are carefully guarded to prevent contamination by wild types.
Cereal chemists were at work, too, learning to control the texture and appearance of bread by bleaching and blending different types of flour. They found a host of chemical additives to improve the consistency of dough and change its flavor, and to increase the shelf life of the finished loaf and improve its nutritional value. Agronomists selected for and bred wheat varieties that resist disease, produce bigger yields per acre, contain more protein, and so on. These advances all contributed to the industrial production of bread, with huge machines producing thousands of loaves per day. Now a handful of very large bakeries produce more than three-fourths of all bread sold in the United States. These same “advances” have also resulted in the fact that most modern bread has the flavor of an edible napkin.
Yeasts are microfungi and are much larger than most bacteria. More than 350 different species exist, with countless additional strains and varieties. In the century and a half since Louis Pasteur discovered that yeast fermentation produces carbon dioxide, which leavens dough, yeasts have been studied in every conceivable light and harnessed to perform hundreds of different tasks, from cleaning up oil slicks to producing antibiotics. Many yeast strains are industrially produced for very specific functions, including commercial bread making. It is important to understand the basic differences between the wild yeasts of sourdough and the commercial baker’s yeast used in most other breads. First, sourdough yeasts grow best in acidic doughs, while baker’s yeast does better in neutral or slightly alkaline doughs. Baker’s yeast is a single species, Saccharomyces cerevisiae
, with hundreds of strains and varieties, while sourdoughs are usually leavened by one or more species in the same dough, none of them baker’s yeast. Baker’s yeast is a highly uniform product that produces an equally uniform texture in bread dough. The wild yeasts are anything but uniform, and they vary from region to region. But perhaps the most impressive difference between the two yeast types is that a single package of instant dried yeast produces just one batch of bread, while the same amount of wild sourdough culture produces loaf after loaf for the lifetimes of many bakers.
In one gram of commercial cake yeast, there are 20 to 24 billion individual yeast cells; in a package of dry yeast, there are 130 billion. By comparison, a cup of sourdough culture as it comes from the refrigerator contains far fewer cells. This book emphasizes repeatedly that you should never use baker’s yeast either in your sourdough culture or in the recipe of your sourdough bread. The addition of baker’s yeast to a culture may overwhelm the wild yeast and destroy the culture. In addition, you risk the introduction of a bacteriophage, or virus, to which the commercial cells are immune but which may kill wild yeast. Plus, if you leaven your dough with baker’s yeast, the open texture characteristic of sourdough may disappear.
The primary secret of sourdough success lies in the art of stimulating a wild culture, just before you use it in baking, into a burst of activity to equal the number of yeast cells found in commercial yeast. The steps we describe to prepare and proof a culture in this book lead to that burst of activity and ensure you will get all the leavening power your loaf needs without the addition of commercial yeast.
Research into Wild Sourdough Cultures
Bakers of every sort welcomed the introduction of commercial yeast in the late 1800s. It greatly simplified the baking process and made it much faster. But something happened to the sourdough flavor. It disappeared! In due time, researchers identified the problem. They found that sourdough bread is the product of not one microorganism but two: wild yeasts make it rise and beneficial bacteria provide the flavor. These bacteria are primarily lactobacilli, so named because they produce lactic acid, which contributes to the sour flavor. But what lactobacilli do, they don’t do very fast. It requires approximately twelve hours for the bacteria to develop fully the authentic taste of sourdough, depending on the temperature of the dough. Extremely fast commercial yeasts, particularly active dry yeast, have shortened the rising process to two hours or less, hardly giving the lactobacilli a chance to get started.
Lactobacilli produce the flavor of sourdough breads by fermentation, which is the primary reason sourdoughs are completely different from, and better than, most commercial breads. Fermentation is that process by which a variety of bacterial organisms act on food products to produce different flavors, textures, and aromas. Examples include the fermentation of milk to produce cheese, yogurt, sour cream, and buttermilk. Many types of sausage involve fermentation of various meats. Fermentation is also essential in the production of various vegetable preparations, including pickles, sauerkraut, olives, and a host of dishes from every corner of the earth. Finally, of course, wine and beer are made through the process of fermentation. But few of us are aware that fermentation is essential to the flavor of sourdoughs. Without sufficient time for that process to occur, the flavor will be lost.
Lactobacilli that produce the famous taste of San Francisco sourdough have been studied by Leo Kline and T. F. Sugihara, two food scientists working at the Western Regional Laboratory of the Department of Agriculture in Albany, California. They determined that many bakeries in the area were using sourdough colonized by identical strains of yeast and lactobacilli. The widespread occurrence of these organisms was not because the bakeries shared their starters with one another, but because these organisms are dominant throughout the San Francisco area. This led them to name this strain of bacteria Lactobacillus sanfrancisco
. In 1970 and 1971, they published the results of their studies on San Francisco sourdough in The Bakers Digest
and Applied Microbiology
Kline and Sugihara identified for the first time the wild yeast Torulopsis holmii
(later reclassified as Candida milleri
, now as Candida humilis
) as the wild yeast responsible for the sourdough process and provided instructions for producing it. The yeast also has an unusual characteristic: it is unable to utilize maltose, one of the carbohydrates found in flour. This assumes special significance, since the lactobacilli require the maltose unused by the yeast. Thus a symbiosis arises between the two organisms in the medium of hydrated flour. Further evidence indicates that the lactobacilli produce an antibiotic that protects the culture from contamination by harmful bacteria. This strong mutual dependence is thought to be responsible for the survival of the culture in San Francisco bakeries for more than one hundred years. It also explains why the culture successfully resists contamination when used in other areas. In 1973, Kline and Sugihara applied for and received a patent based on those studies so that, in the words of the patent, “the unique product (San Francisco sourdough) can be manufactured efficiently, economically and in any location regardless of climate or topography.”