::  Using Sourdough starters to create flavorful Breads
     by Stuart Cantor, Bakery Management Magazine Editor

 Americans have expressed renewed interest in the traditional tastes of the old world. Consumption of flavorful specialty breads is on the rise, as consumers discover yet another comfort food.

 Although these foods were once only seen in artisan bakeries, they are now showing up in mainstream supermarkets throughout the country. At almost any supermarket, consumers can purchase brioche, panettone, pain au levain (French leavened bread), pizza doughs, ciabatta and sourdoughs.

 To obtain the appealing aromas, golden crusts and hearty textures of these bakery foods, bakers rely on special bacterial cultures known as sourdough starters. Bakeries can opt for two methods when flavoring bread with sourdough starters: a natural sourdough process or a prepared sourdough starter system.

 The natural sourdough process dates back to the mid-1800s, and involves a complicated, step-oriented process of combining flour, water and yeast. Over time, this combination of ingredients grows into a starter that is incorporated into a dough system. Although this process produces uniquely flavored bread, the time, equipment and space constraints required to us this process makes it difficult for high-volume bakeries to use.

 On the other hand, bakers can use a prepared sourdough starter system, which gives them the benefit of flavorful bread, while reducing production times. When using the prepared sourdough starter system, bakeries add a prepared sour starter to the dough. There are various types of sours, including liquid sours, powdered sours, sour concentrates and chemical sours.


GETTING CULTURED

 Sour starter cultures consist of lactic acid-producing bacteria, predominantly from the Lactobacillus or Pediococcus species. Some lactic cultures, especially those from Europe, may contain as many as 15 separate strains of bacteria. The strain, Lactobacillus sanfrancisco, is used to duplicate the famous tangy sourdough breads from the West Coast. The optimum pH for lactobacilli is 5.0 to 5.5, which is the initial pH of a sourdough with 5% to 50% inoculum. Most sourdoughs have a pH at the end of the fermentation process of around 3.6 to 4.2 (L.sanfrancisco does not grow below pH 3.6).

 There are two main types of lactic acid bacteria: Homofermentative and heterofermentative. Homofermentative bacteria, such as L. plantarum produce lactic acid under anaerobic conditions from maltose or glucose in the dough. These bacteria also produce an elastic crumb in bread. Because homofermentative bacteria do not produce carbon dioxide, yeast must be added to ensure leavening of the dough. On the other hand, heterofermentative lactobacilli, such as L. brevis or L. sanfrancisco, produce a variety of organic acids, including lactic aid, ethanol and carbon dioxide gas.


GETTING STARTED

 A very important aspect of making sourdough is the amount of starter used, and the amount of time that has passed since the starter matured. Typically, about 20% to 40% of the total flour should come from the starter. The higher the percentage of starter, the less proofing time it will stand. In other words, if 40% of the flour comes from the starter, proofing for more than four hours may flatten the loaves. Using an old starter also causes reduced loaf volume.

 When a starter is fed, the smallest amount of old starter should be used to achieve a very active ferment when the dough is mixed. If the old starter is very active, it is best to use only 5% to 10% by weight as an inoculum. Starters that are not fresh produce extremely slack dough, which will lead to machine-ability problems.

 Generally, a strain of conventional baker's yeast, such as Saccharomyces cerevisiae, is used with a blend of lactic acid -producing bacteria, such as Lactobacillus plantarum and Lactobacillus brevis in cultures in a ratio of 1:100. The role of yeast in a sourdough starter is to leaven the bread. Increasing salt concentrations inhibit the growth of lactobacilli, but yeast is generally more salt tolerant. However, yeast is strongly inhibited by acetic acid, and to a much lesser extent by lactic acid. Although the acid sensitivity can be overcome by proofing longer or adding more yeast, bakers need to be cautious not to add too much yeast, which will cause the bread to be overwhelmingly yeasty in flavor.

 The temperature used to maintain the starter will dramatically affect the kind of bacteria that survive. As a rule of thumb, higher temperatures (above 90º F) will favor acid production by the bacteria, and cooler temperatures (below 75ºF) will favor the more aromatic compounds produced by the yeast. A good compromise is between 80ºF and 85ºF. One exception to the rule is the heterofermentative bacteria, L. brevis and L. sanfrancisco. Both of these organisms prefer cooler temperatures between 80ºF and 90ºF. Fermenting at cooler temperatures favors the production of acetic acid, or vinegar. "A good balance of acetic to lactic acid in a 1:3 ratio is essential for a clean sourdough taste", Clifford Caron, Lallemand/American Yeast's vice president of bakery product development, says.


FEEDING FRENZY

 Prepared sour starters come in a variety of forms, including liquids, powders and sour concentrates. Rye and wheat lour are the two main sources of sour cultures. Rye will give more flavor and a darker curst color, and wheat will give a lighter color, which is typical of French breads. A powdered sour is produced by taking flour and allowing it to ferment with selected lactic acid bacteria strains until ripe. After this multi-stage fermentation process is complete, the culture is then carefully sprayed or drum dried to produce a powder with about 5% moisture content.

 Dried cultures are easier to use than liquids, and are more stable - they can be stored for one year. "Use levels for powdered cultures are generally between 0.05% to 15% based on flour weight in the sour", Caron says. "This means that if 50% of the flour in the final dough comes from the sour, then the starter usage would be only between 0.025% to 0.075% of the total flour weight. Sour concentrates are usually used between 4% to 10% depending on the product."

 To produce breads, a powdered culture is added to water and flour. The mixture ferments for 18 to 24 hours. At this point, the dough will have increased from two to four times its original size. After 24 hours, this leavened mass, called a levain or sponge, can either be fermented or cooled. To make a batch of dough, the baker mixes flour, salt, and baker's yeast with a portion of the sponge and the dough. Fermentation times vary with temperature, from about six hours at 86ºF to 12 hours at 68ºF.

 Liquid sours are used between 10% to 30%, based on the flour weight, but only have a shelf-life of one week when refrigerated. The main advantage of using a liquid starter over a powdered starter is faster flavor development. Because these ready-to-use cultures have already been alive for several days, a full-bodied fermentation flavor will develop much quicker in a no-time dough, resulting in less expensive production costs.

 "The great benefit of liquid sours over their dry counterparts is that the more volatile and flavorful products of yeast fermentation have not been stripped out by the drying process," Caron states. "Also, the secondary benefits of crumb modification are present. The acid environment produces a softer crumb, which retains moisture and thus prolongs shelf life. The drawback, however, is that the sour needs to be used quickly, as the good bacteria die fairly rapidly."


ENHANCING FLAVOR

 In some cases, bakers can use powdered or liquid mixes, which contain additional acids, to augment the flavor of breads. "For example, while lactic acid tastes sour, it does not smell sour. Acetic acid, on the other hand, is more volatile than lactic acid, and thus, its impact on flavor is more pronounced. Additionally, acetic acid is important as an inhibitor of spoilage organisms such as molds or rope-causing bacilli." "Some San Francisco-type sourdough breads show the blending of both worlds of natural and chemical sours to obtain a product with a nice acidic bite and impact."

 And, higher production throughput does not always have to mean lower quality taste. "For those bakeries using no-time doughs, adding powdered fermentation flavors is a natural way to enhance product appeal and gain the effects of a long-time natural fermentation process". Spray dried or drum dried fermentation flavors can be added to multigrain, whole wheat or artisan breads to give them a more rounded and complex flavor.

 Many bakers usually add high levels of sugar and/or sugar derivatives (honey, molasses) to whole wheat breads to mask the taste of the bland, somewhat bitterly flavored high bran content. "However, adding fermented sour flavors to whole wheat-containing products at 1.5% to 3% (flour basis) gives a better rounded flavor and improved aroma. The flavor is added with the other ingredients at scaling, so it' easy to use and can e labeled as all natural", Sausville explains.

 The combination of bacteria and yeast create complex aromatic flavors using acids, alcohols, ketones, and esters that react with the amino acids in flour during baking to produce more that 200 different flavor compounds. These flavor compounds contribute to the subtle and distinctive taste and aroma of fresh baked bread. Because the consistency and quality of prepared sour starter cultures has improved markedly over the last five years, volume bakers should be poised to take advantage of the growing trend towards specialty flavored breads.