Pubdate: December, 1944
Source: Bulletin 465: Annual Report of the Director, Agricultural Experiment Station, University of Wisconsin, Madison (part one) - "What's New in Farm Science"
Page: 50

THERE ARE good possibilities of improving the quality of hemp fiber by retting the crop in water-filled vats with the aid of bacteria, a study by Mary Jo Rickard, Wayne Umbreit and Elizabeth McCoy indicates.

This investigation had the cooperation of Kennth Buchholtz of the U.S. Dept. of Agriculture and A.H. Wright of the Agronomy Department as well as support from the Atlas Hemp Mills.

In the past, Wisconsin hemp has been "dew-retted," meaning it is left in the fields to let the weather do the work. This produces fiber of extremely variable quality; in unfavorable weather, it may be so weakened as to be useless.

As conducted experimentally at this Station, vat retting involves submerging the hemp in water, inoculating with suitable bacteria, and allowing the retting to proceed at 99 degrees F. for two to four days.

One phase of the investigation involved testing numerous types of pectin-fermenting bacteria to determine their suitability for this process. Those tested included many native Wisconsin soil bacteria, as well as organisms used in vat-retting flax and hemp in Italy and Russia. In later work the investigators settled on Clostridium felsineun, the principal type used in Italy.

Indications are that successive batches of hemp can be retted in the same water. This practice should be an aid to efficient and economical operation, and also simplifies the waste-disposal problem.

Acid is produced in the early stages of vat retting, but the pH soon becomes stabilized at around 5.5, which is favorable for rapid retting. There may be no need for pH control, or for additions of nitrogen or other supplements, if suitable initial conditions are supplied. Although retting usually is completed in 60 to 72 hours, there is no harm in leaving the fiber in the vat as long as 96 hours, a point allowing flexibility in schedules of factory operation.

Although vat retting has given encouraging results at this Station, it must be borne in mind that the work has been conducted on a small scale in the labaratory, using vats holding about three gallons of water and air-drying the retted fiber, and that the product has not been given spinning tests.

It remains to be seen whether vat retting will work equally well in commercial hemp mills, where large-scale operation and methods of working up the retted fiber remain to be worked out.