Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)


Information as to the nature of the chemical changes that occur during the biological retting of hemp is scanty. Flax retting has been far more extensively studied, mostly by European workers; but it has frequently been implied that the principles involved and the problems met with are similar in flax and hemp retting. This subject is well reviewed by Thaysen and Bunker (9). It has been repeatedly stated that the essential biochemical change is the decomposition of the pectic substances present in the middle lamella of the parenchymatous tissue cells as a result of which the bundles become readily separable from the wood and the epidermis. It cannot be said, however, that there is clear analytical evidence for this statement. Moreover, there must be concurrent utilization of other tissue constituents, and progressively an attack on the fiber bundles, manifest in practice by the ultimate weakening and deterioration that occurs in over-retting. The processes that occur in retting constitute in fact the first stages in the decomposition of the hemp straw. Desirable changes that result in the liberation of the fibers pass imperceptibly into undesirable changes that result in impairment of quality. There is no certain way of determining when retting is complete. Reliance ordinarily is placed upon the judgment of the observer, which is based on the appearance of the straw and on simple mechanical tests. Whether the completion of retting under controlled conditions in tanks can properly be judged by standards similar to those applied to field-retted material is doubtful. Although the ultimate result is similar in that the fibers can be separated from the straw, it is not necessarily to be expected that the biochemical changes brought about by populations so different in character as those active in field retting, and those in deep tanks, are identical. In order to obtain information on the nature of the changes that occur to the constituents of the straw, samples of field retted and controlled retted hemp have been analyzed in some detail.



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