Dormancy: Barley Barely Germinating
By: Malteurop Malting Company

Why isn’t barley ready to be malted right after it is harvested? What exactly is dormancy and is it a good thing?

J.F. Pelton wrote that dormancy is “an adaptive trait that causes seeds to germinate at a time, or place, favorable to the subsequent survival of the seedling and adult plant” (Butler University Botanical Studies, Vol. 13, 1956). It’s all about surviving long enough to grow into a new plant the next season. A reasonable period of post-harvest dormancy prevents the kernel from sprouting out in the field. Those of us who lived through the 2014 North American crop saw widespread pre-harvest sprouting (PHS), which accelerates the kernel’s “biological clock”, if you will, causing it to die prematurely and become unusable within a few months. There were a lot of ulcers and grey hair that year!

So why was the 2014 crop such a nightmare? Mother Nature was not kind, and sent way too much moisture too close harvest for our newer varieties. Over time, these varieties were selected for shorter and shorter dormancies because of working capital, insufficient storage capacities, and greater abilities to produce enzymes. The timing of new varietal trials also favors varieties that break dormancy quickly so that unsuitable varieties can be eliminated prior to the next stage of field trials. The growing season is shorter in North America than most barley growing areas in Europe. So accelerated growth is more common in North American varieties. Of the few overseas varieties that can grow here, the ones with the longest dormancy tend be those with European germplasm that have targeted craft brewers’ specifications.

There are a number of factors that influence dormancy. As indicated previously, genotype, developmental stage, and environmental conditions like water stress, temperature, spectral quality of light, and daylight hours are key variables. These conditions affect the hormonal balance within the kernel, despite their very low concentrations. Abscisic Acid (ABA) and Gibberellic Acid (GA3 in barley and wheat) are the most influential of these hormones. 

Abscisic Acid is a 15-Carbon terpinoid discovered in the 1960’s and part of the plant’s stress response. ABA inhibits the tendency of immature seeds to germinate while still on the mother plant (L S. Green et al.,Plant Physiology, Vol.114, 1997) and declines during seed germination (J. D. Bewley, The Plant Cell, Vol. 9, 1997). Genotypes susceptible to PHS have lower levels of ABA in the embryo (R.W. King, Planta, Vol. 132, 1976).

Gibberellic Acids are 19 or 20-Carbon terpinoids first identified in the early 1800s that promote growth and elongation in cells. G. H. Palmer noted (J. Inst. Brew., Vol. 80, 1974) that germinating barley embryos secreted GA3 to stimulate hydrolytic enzymes to modify the endosperm. This occurs in the soil and in the malthouse. GA3 is especially important in stimulating the production of Alpha-amylase during germination.

Which brings us to the balance point. A high ABA: GA3 ratio maintains dormancy, until additional GA3 is synthesized to decrease the ratio and therefore, dormancy. Our very own Alberto Jiménez-Díaz, Quality Service Senior Manager, did his graduate work at North Dakota State University on this topic. Alberto’s work showed how the metabolites of ABA and GA3 differed in quantity between varieties related as closely as the 6-rows Robust and Stander, as well as how their intensities changed as they got further from ripening in the field:

Robust is a slightly less enzymatic, more PHS resistant variety than Stander. Stander is a higher yielding variety that fell out of favor because of its higher susceptibility to Fusarium infection and resulting high DON levels. Ironically, Robust was one of three varieties crossed to breed Stander. Building upon the work of many great scientists before him, Alberto used metabolomics to illustrate how dormancy is broken and the role of genotype in determining when varieties are ready to make great malt!