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create excessive acidity and inhibit the wild yeast. In contrast, using quart (liter) jars means you must discard part of the activating culture at each feeding or the mixture will overflow the jar. This dilutes the acidity slightly at each feeding. In addition, with glass jars you can see activity inside the developing culture. The jar lid should not be tightened, but put on loosely.
    “Washing” a Culture
    During the first step of activation, the amount of flour added to the culture is almost three times the amount in the dried culture. It is at this point that contamination by nonsourdough organisms present in most flour sometimes, though rarely, occurs. Contamination is more likely when the initial activating temperature is not high enough, causing slow acidification by the lactobacilli. Evidence of contamination usually appears in the first 24 hours: the culture may produce sufficient bubbles and foam to suggest that the culture is activating prematurely, and it may give off an unpleasant odor. Contamination can usually be corrected by “washing” the culture to dilute the contaminating organisms (as well as the good ones) and starting the 90°F (32°C) proof again, giving the lactobacilli another opportunity to acidify the culture.
    To “wash” a culture, mix thoroughly and discard all but about 1 cup (240 ml) of the culture. Then fill the jar almost to the top with warm (75° to 85°F/24° to 29°C)water while stirring vigorously. Again discard all but about 1 cup (240 ml). Now feed it ⅔ cup (90 g) of flour and enough water to maintain the consistency of thick pancake batter. Proof at 90°F (32°C) for 24 hours. There should be a marked reduction in activity as contamination is reduced. After 24 hours, feed ⅔ cup (90 g) of flour and enough water (about ½ cup/120 ml) to maintain the consistency. Reduce the proofing temperature to about 70°F (21°C) and continue discarding and feeding as above every 12 hours at this lower temperature. When normal fermentation takes over and the culture becomes fully active, the layer of foam and bubbles will reach almost to the jar top 2 to 4 hours after the last feeding. The culture is then ready to use or refrigerate. If the culture does not begin to revive in 2 to 3 days, the washing process should be repeated.
FULLY ACTIVE CULTURE
    One of the most critical factors for success with sourdoughs is the fully active culture. For well over a hundred years, commercial sourdough bakers rebuilt their cultures several times each day. Some still do. However, many home bakers bake less than once a week, and their refrigerated cultures are always partially dormant, depending on how long they have been in the refrigerator. But the lactobacilli always remain somewhat active, and the culture becomes increasingly acidic the longer it rests. When a refrigerated culture is warmed and fed flour and water, the organisms begin to reactivate, but the activity of the wild yeast is often inhibited by the increased acidity of the culture.
    To reduce a culture’s acidity, when you take it out of the refrigerator, fill the culture jar with warm water while stirring vigorously. Leave slightly more than 1 cup (240 ml) in the jar and discard the excess. (If you will be baking more than one loaf and so anticipate needing more than one jar of culture, use the excess to build additional culture in the following steps.)
    Feed the culture in the jar ⅔ cup (90 g) of flour and sufficient water to restore the consistency of thick pancake batter. The jar should now be slightly more than half full (we are assuming a 1-quart/1 liter jar).
    Proof at 70° to 75°F (21° to 24°C). If the culture has been in the refrigerator for less than 2 weeks, it is only mildly dormant and will usually become fully active in approximately 2 to 4 hours when proofed at room temperature. If it does not respond well, an additional feeding may be necessary. As soon as it forms foam and bubblesthat increase the total volume by about