The incubation of tempeh is a delicate balance of temperature, airflow, hole size on bags or trays, and relative humidity. Some common problems observed are as follows:
1. Hole size in incubation bags. This is an important feature and somewhat varies based on the incubator that the product is placed in. If the airflow, temperature, and humidity are all adequately controlled, it is possible to get away with a larger perforation than in an incubator with inadequate controls. As a rule, 1.5 mil polyethylene bags with size 7 sewing needle perforations every one-half inch will produce a quality product.
2. Incubation. During the first 12 hours, the inoculated beans are just heating up and no cooling is required, assuming the temperature of the incubator is around 88 °F (32°C). After 12 hr, a small amount of water begins to collect on the inside of the bags. At 14 hours, fermentation of the Rhizopus spores has begun in earnest and active cooling of the air must take place. If the inoculated beans reach a temperature above 92°F (33.3°C), conditions are no longer ideal for Rhizopus spores but are ripe for a different set of organisms such as those of the Bacillus group. Rhizopus can be severely damaged by heat of over 92°F ( 33.3°C).
At temperatures above 96°F (35.6°C), Rhizopus is killed and the product will be discarded. If internal temperatures don't reach 96°F (35.6°C), the tempeh can usually be saved. Heat-damaged tempeh may be taken out of the incubation room and kept out at room temperature (approximately 70° F or 21.1° C), and it will start to grow over the damaged areas with new white mycelium.
The ideal relative humidity for incubating tempeh is between 50% and 75%. Airflow should be kept in the 120-cfm range to prevent overdrying of the product, which can lead to premature sporulation. One design for a tempeh incubation room that we have loosely followed was presented by Chananyah Kronenberg in the Summer 1983 issue of Soyfoods Magazine. The incubation room suggested in the article is presented in Fig. 5 (15).
3. Premature Sporulation of Tempeh. During incubation, sometimes black spots will show up around the holes of the bag. These are actually the spores of the tempeh culture and are not harmful to eat though they often lead to the consumer discarding the product as inferior. In some parts of Indonesia, black, overripe tempeh is sold in the market and used as a spice in much the same way a well-aged cheese may be used. But by and large, the black spots are the bane of the commercial tempeh-maker and should be avoided who ever possible. An albino form of Rhizopus oligosporus spores to be refined and sold commercially is highly desirable.
Tempeh sporulates when a threat to the culture's existence arises. This can be from excessive drying due to too much airflow, heat, or lack of adequate humidity. When one of the above causes is to blame, the tempeh develops black spots around the perforations of the incubation bags. A pattern of black dots can be clearly seen on the wrapper.
Another kind of premature sporulation appears as a general blackness underlying the white mycelia on the product. This type of sporulation usually can be traced back to inadequate cooking times of the beans or the grains. If the beans or grains are undercooked too much, they will not fully hydrate and the product will blacken all over due to the inadequate moisture in all the beans.
4. Contamination. Whereas Rhizopus oligosporus is generally a very hardy mold that grows so strongly and quickly that other organisms are crowded out, there are three basic tempeh contaminants that can cause problems. The most severe contaminant facing tempeh makers are those from the Bacillus family. Bacillus contamination results from too much heat and too much moisture. It has a distinctive odor similar to a wet baby diaper. The cake will be dark brown and slimy to touch. Bacillus is a very virile bacteria and must be dealt with swiftly and thoroughly. Many tempeh makers have reported bacillus outbreaks in their plants that take weeks to resolve. The best move is to discard any Bacillus-contaminated cakes and immediately wash down floors, walls, and ceilings with a weak chlorine solution or quaternary ammonia. Bacillus problems seem to be most common in tempeh plants that share space with tofu-making operations.
Besides Bacillus, Pseudamonas (pink mold) and Aspergillus (green,''bread mold'') are the only other microorganisms that will grow on tempeh in one tempeh processing plant. It is a good manufacturing process to have tight control over the starter culture, which can also lead to contamination problems.
5. Tempeh Starter. Due to problems that can occur with contamination, the Indonesian practice of starting successive batches of tempeh from previous tempeh batches left to ripen in the incubator will post risks. Buying a good pure culture from a reputable lab and extending this on rice or other grains every month is a good manufacturing process. Basic instructions for producing your own tempeh starter can be found in the Book of Tempeh by William Shurtleff, Ten Speed Press, Berkeley, CA (16), and The Complete Book of Tempe published by the American Soybean Association (17).
6. Vacuum Packaging. About 85% of all tempeh sold in the United States today is sold vacuum-packaged. The first vacuum-packaged tempeh in the United States was introduced around 1980 by Pacific Soyfoods, a San Francisco company. At this writing, the four largest North American tempeh shops (Lightlife, Turtle Island Foods, White Wave, and Northern Soy) all vacuum-package their tempeh. After packaging, these tempeh cakes are pasteurized and sold with a 60- to 90-day refrigerated shelf life.
During vacuum-packaging of tempeh, several changes occur. First, and most obvious, is the disappearance of the white tempeh mycelium, which is surpressed into the substrate during vacuum-packaging. The result of this is a tempeh cake that appears brown and the individual beans are easily seen. Second, it is the belief of this author that the resulting tempeh often changes in flavor and texture, leaving the resulting product slightly more bitter and smoother in texture. The cause of this change in taste and texture needs to be studied further, especially the change in flavor.
The reason behind vacuum packaging is that the tempeh can now be sold refrigerated, alongside the tofu with a longer shelf life. Given the modern food distribution systems and enhanced movement of refrigerated products versus frozen products, it is hard to argue against the wisdom of vacuum-packaging tempeh. On the other hand, the changes brought on by this form of packaging create a different quality product, not necessarily for the better.
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