Connection between barley husk structure and its quality

The barley husk consists of two leaf-like structures: the palea covers the crease side and the lemma covers the back of the grain overlapping with the palea. A cementing layer secreted by the pericarp epidermis fills the interface between the pericarp and the husk. In recent years, susceptibility to hull peeling or skinning has been reported to be a problem with some new European, Australian and North American barley varieties. In the malting process, the husk protects the kernel and the growing acrospire, and, in brewing, it acts as a filter medium in wort separation. If the husk does not properly adhere to the kernel, it will cause problems such as dust, difficulties in weighing and lauter tun performance in breweries. The aim of the work was to compare the chemical and physical quality of husks of barleys with high and low husk damage and to develop analytical methods for breeders and malt-sters to evaluate the potential for husk damage. The research was especiaIly focused on determination of the structural features indicating hull quality and evaluation the importance of the cementing layer to hull adherence. The chemical and microscopic analyses indicated that the physical structure of the husk is more important than its chemical composition for good husk adherence. The cementing layer stained red with Oil Red O, indicating that it is a cutineous substance. Microscopic evaluation of the samples showed that the husk usually did not separate along the cementing layer between the pericarp and the hull. Instead, the husk layers with large thin-walled cells were broken. In a preliminary comparison of seven barley varieties, a thin dorsal vein and a thin layer of parenchyma in the lemma appeared to indicate less easily damaged husk than a strong dorsal vein and thick layer of large thin-walled parenchyma cells. Analytical methods were developed for visual and mechanical evaluation of the husk damage. They are suitable for screening purposes by breeders and for quality control by maltsters. The most critical steps affecting husk damage in malting operations were identified by using the visual method, which could be used for the development of the best practices in the entire production chain. A clear difference in husk quality between varieties was detected. Evaluation of barleys grown in various locations and crop years confirmed that husk quality is a varietal characteristic, but growing conditions also have a marked effect.