Last revised February 15, 2010
Bean, alfalfa, or broccoli sprouts, and other vegetable sprouts grown for food purposes, are simply miniature plants, harvested just after seed germination. Production practices are those techniques that provide the optimum germination conditions, moisture, temperature and oxygen in an environment that allows the "harvest" of the sprouts at their optimum eating quality, while at the same time allowing efficient cleaning and packaging. This guide discusses primarily the production of bean sprouts, but the principles of bean sprout production described below may be applied to other sprout crops.
Note: Various other crop seeds may be sprouted. The most common are alfalfa, radish, cress, lentils and several cereals. See University of Idaho circular number 852 for more information. For information on commercial equipment for sprout production, other technical information, and seed for sprouting, contact:
International Specialty Supply
820 E. 20th St.
Cookeville, TN 38501.
An additional source of information on sprout production is: Sprout Publications, POB 62, Ashland, OR 97520.
MICROBIAL CONTAMINATION ISSUES
As sprouts have become more popular, some food safely issues have emerged. Some outbreaks of foodborne illnesses have been traced to E. coli 0157:H7 and Salmonella on lettuce, muskmelon, and sprouts; Shigella on parsley and lettuce; and Cyclospora on raspberries.
Chemical sanitizers have been tested to reduce surface contamination of seed by some of these organisms. Internal seed infections must be dealt with in other ways. This work is still in progress. Decontamination procedures are not simple and have a number of important implications. The USDA National Institute of Food and Agriculture has a Food Safety site. The Guide to Minimize Microbial Food Safety Hazards for Fresh Fruit and Vegetables is available from the FDA.
Bean sprouts are produced primarily from mung bean seeds. Some soybean and adzuki bean sprouts are also used. Preferred varieties are those that have small seed size. With small sizes the cotyledons and seed coats are less objectionable, or are more easily removed from the finished product.
Mung Bean: Smallest seeded varieties are Oklahoma 12 and Oriental. Larger seeded types are Jumbo and Berken.
Adzuki Bean: any small seeded adzuki. A variety called Chinese Red or Chinese Red Adzuki is sometimes substituted for adzuki bean even though it is not an adzuki.
Any container that provides drainage and aeration, is rustproof, and is easy to sanitize is adequate. Stainless steel and plastic are most commonly used. Size depends on the scale of the sprout operation and the amount of bean seed to be sprouted. Mung beans increase in size about 6-fold when sprouting is completed. This can be used to determine the volume or pounds of seed needed and the size of sprouting container required.
When using round sprouting containers such as 2.5 to 5-gallon plastic pails equipped with drains, use about 3-4 lb of seed in a 2.5 to 3-gallon pail or about 5 to 7 lb seed in a 3 to 5-gallon pail.
Some sprouting operations will use perforated-bottom plastic trays in which the sprouts are to be marketed. This is preferred or even required by some buyers.
Under proper conditions 4-5 days are required from the start of the sprouting process until the sprouts are ready for consumption.
Use only untreated seed, not seed treated for planting purposes. Treated seed is usually dyed, but may not be. Be sure to check if this is not known.
Wash seed thoroughly, picking out any foreign material, and obviously blemished seeds.
Soak seed in lukewarm water (90-95 F) for 2 to 4 hours, or at room temperature (68-72 F) overnight. This is to bring all the seed to a uniform moisture content, and to begin the germination processes in the seed. Drain and rinse. Place in sprouting containers if different from the soaking container.
For thicker, yet tender sprouts, which are preferred, apply a weight of about 0.5 ounce per square inch of surface area across the seed (a 2-lb weight would be needed over the seed for an 18-inch diameter pail). Weights should be cushioned. This can be done by placing a porous pad between the seed and a perforated piece of rigid plastic (for ease of cleaning) or board on top of which the necessary weights are set. Air and rinse water temperature manipulations may also be used to manipulate sprout characteristics.
Maintain a sprouting temperature of 70-80 F during the entire sprouting period (about 5 days) for best quality sprouts. Temperatures of between 80 and 85 F result in slightly quicker growth but produce more elongated sprouts. Sprinkle thoroughly with lukewarm water (70 F) every 4 to 6 hours, allowing the water to drain completely each time, for maximum flushing of accumulated carbon dioxide and metabolic wastes and to provide adequate aeration and oxygen flow. Watering frequency may be reduced to 6-8 hour intervals per day during the fourth and fifth days. Water temperature and frequency of watering are particularly important during the second day of sprouting to maintain the desired temperature, since this is the time at which the greatest amount of heat is generated by the sprouting seeds. Sprouting seed must not be allowed to overheat or stand in water since anaerobic conditions will develop, the seed may die or decay, and bacterial contamination may result.
Light is not necessary in the germination process. Light will cause some green color to develop in the primary leaf. Greening is considered a defect in many types of sprouts.
Sprouts are ready to harvest after 4-5 days. If used, remove the weights and rinse the seed coats out of the seed as much as possible. Removing excess water just before packaging, using a centrifuge or other means, enhances keeping quality if care is exercised to avoid damaging the sprouts. The sprouts are then ready to use, process, or package for sale.
Presently, sprout production and use has increased. An endless variety of seeds are used. In general, sprouting requirements are similar to those described above. Variations in production include the use of small amounts of light for the greening of leaves of some sprouts such as cress, and the obvious lack of need for weights for others such as radish. Temperature is the most important variable with different types of sprouts. Keep in mind whether the vegetable is a cool or warm season crop when experimenting with different sprouting temperatures.
Sprouts are grown from peas, chickpeas (garbanzo), lentils, alfalfa, radish, cress, buckwheat, rye and wheat, but the market generally handles primarily mung, alfalfa, radish and cress sprouts, and in some cases mixes of some of these.
Sprouts of broccoli and other brassicas have recently been found to contain large quantities of inducers of enzymes that protect against carcinogens. Levels of these inducers are 10-100 times larger than found in broccoli heads. The title of this research, published in Proceedings of the National Academy of Sciences (94:10367-10372), is "Broccoli sprouts: An exceptionally rich source of inducers of enzymes that protect against chemical carcinogens." Other brassica sprouts containing large quantities of the inducers include arugula, brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, crambe, daikon, kale, kohlrabi, mustard, red radish, turnip, and watercress.
POSTHARVEST HANDLING AND STORAGE (Quoted or adapted from USDA Ag Handbook 66 and other sources)
Mung bean plants are classified as being chilling sensitive; however, the sprouts are highly perishable and store best at 32 F and 95 to 100 percent relative humidity. The respiration rate of mung bean sprouts is high, and the rate increases sharply with temperature. The shelf life decreases sharply with increases in holding temperature. Symptoms of deterioration are darkening of radicle and cotyledons, development of dark streaks on the hypocotyl, and eventual development of sliminess, decay and a musty odor. The sprouts remain in good salable condition at 32 F for 7 to 9 days. Shelf life of sprouts kept at 32 F but exposed daily to 68 F for 30 minutes can be reduced by 50 percent, which emphasizes the importance of immediate cooling and holding at 32 F. At 36.5 F, 41 F and 50 F, the maximum salable life is 5.5, 4.5, and 2.5 days, respectively. Perforated film packaging has been reported to be helpful in maintaining the quality of sprouts of mung beans, soybeans and adzuki beans.
The Pacific Northwest Disease Control Handbook has no control entries for this crop. Proper sanitation can reduce the risk of many diseases. Using seed from reputable sources reduces risk from "seedborne" diseases.