  Retting is the partial rotting of the hemp stalk. It permits the fiber in the stalk to separate easily in long strands from the woody core. The fiber strands break if unretted stems are bent or broken. In this country the usual practice is to ret hemp by allowing it to lie on the ground, where it is exposed to rain and dew. This method is called dew retting. Dew retting is dependent upon dews and rains to furnish the moist conditions necessary for the growth of the molds that cause the retting. In warm, moist weather the retting may require 1 to 2 weeks, but usually 4 to 5 weeks is required for retting in Kentucky and Wisconsin. Hemp has remained spread under snow in Wisconsin until spring without serious injury, but more often hemp left under snow all winter is overretted and ruined. If hemp stalks are lifted from the ground before they are sufficiently retted, the fiber will not separate easily from the woody hurds (small pieces of the woody core of the plant) in milling. However, if the retting is permitted to go too far, the fiber separates very readily from the core, but the adhesive substance between the individual fiber cells in the long strand breaks down and the fiber is weak. Hemp further overretted produces mostly short broken strands of fiber called tow fiber, which is less valuable than the long parallel strands of fiber called line fiber. Nowhere in the growing or processing of hemp is good judgment more needed than in determining the time to end the ret. Experience and good judgment are necessary to determine just when the hemp stalks should be lifted from the field and bundled. The lifting and shocking stops the retting action. The value of the fiber can be cut in half or entirely lost by several days' overretting in warm weather. In Kentucky, hemp spread immediately to ret after harvest is apt to sunburn, or sunscald. It is common belief that the hot, bright days in August and September in some way cause deterioration of the fiber if spread for retting. Sunburned fiber is uneven in color, usually has less strength, and possibly is drier and more harsh than fiber not sunburned. In order to avoid sunscalding, the hemp is shocked after being harvested and not spread for retting until the cooler days of November. In locations having climatic conditions similar to those prevailing in Wisconsin, sunscald of hemp is rare. In dew retting the spread stalks should be turned once or more during the retting period. This aids in bleaching the stalks and results in fiber of more uniform color and quality. The turning is In turning the straw the workmen start in the middle of the field, turning the first swath into vacant center space. The second swath will be turned to lie where the first swath had been, and so on. Care should be exercised in turning to prevent the stalks from tangling. The more hemp is handled, the more tangled the stalks may become. Tangled hemp is more difficult to process and produces a high proportion of tangled, short, tow fiber. A few days too long in the field may make the difference between retting and rotting. Therefore, it is most important that inexperienced farmers obtain the assistance of the hemp-mill superintendent or an experienced grower in determining when to stop the retting. Dry hemp stalks should be tested when possible to determine the degree of retting. Three to six stalks are taken in both hands and bent back and forth to perform the break test. If properly retted, the fiber should not break when the woody core breaks. The hurds should fall free of the fiber in the breaking and shaking between one's hands. If the hemp is only partly retted, some hurds will adhere to the loosened fiber. Unretted hemp fiber is usually green or light yellow. Dew-retted hemp is usually slate gray or black. After the fiber is broken free, its strength should be tested by breaking All indication that the retting end point is near is that the hemp makes "bowstrings." In a small percentage of the stems, less than 1 to 5 percent under certain conditions, the middle of the stalks appears to ret first. The fiber comes free from the middle and forms a string fastened at the top and bottom of the stem, not unlike a bowstring. If bowstring stems are found, a sample of the hemp should be taken to the hemp-mill superintendent as soon as possible for verification of the retting end point. The bowstring condition is only a supplementary aid in determining when to stop the retting, and it may or may not occur in properly dew-retted hemp. Some experienced hemp producers use the peeling test for determining the degree of retting. This is accomplished by peeling the fiber away from the butt ends of the stems. If properly retted, the fiber should peel freely from the woody core of the stem. If the hemp is not sufficiently retted, the fiber will break after a few inches have been peeled. This free-peeling stage is desirable for breaking hemp on hand breaks. Where hemp is to be processed by machinery the retting need not progress quite so far as is necessary for hand breaking. |
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