Biochemical Reaction
Enzymatic reactions in flax retting modify the pectin structure of the middle lamella to release individual fibre bundles from the surrounding stem tissue. This biochemical breakdown relies on homogalacturonan de-esterification, a process that removes methyl ester groups from the pectin backbone. The reaction makes the pectin susceptible to further degradation by endo-polygalacturonase enzymes.
Process Control
Acidity levels and temperature in the retting tank govern the rate of enzymatic activity during the retting phase. Spun-fibre mills in China monitor the pH of the retting bath to prevent over-retting, which degrades the cellulose and reduces fibre strength. During homogalacturonan de-esterification, pectin methyl esterase enzymes lower the degree of esterification from seventy percent to below thirty percent.
This reduction enables calcium ions to cross-link the pectin chains, forming a gel that is easily washed away during the subsequent scutching stage. Lab technicians log these values in the daily retting batch report.
Fibre Integrity
Fiber strength is evaluated after scutching to determine the quality of the flax bundle. Incomplete de-esterification leaves the fibres glued together, resulting in coarse, stiff bundles that are difficult to spin. Conversely, excessive retting weakens the flax cell walls and lowers the yarn yield.
The mill’s test report grades the flax based on the residual pectin content and fibre flexibility.
