Have you ever looked closely at a kernel of malt? I mean really closely? Depending on the variety of barley the malt was sourced from, you might have observed a teeny tiny hole on the side of some of the kernels – as if they were shot by a Leprechaun wielding the world’s smallest gun!

Anyone who has a general understanding of the insect pests that are harmful to stored grains may already think they know where this article is heading. We must obviously be discussing Granary Weevils, the beetles that carry out their life cycle inside stored grains and emerge from the kernels as flightless adults who remain amongst the grain to feed and reproduce, right? Wrong! In this article, we will explore a lesser known, but much more interesting cause of holes in malt. We will also discuss the signs of a true Weevil infestation so that you will be able to understand whether or not your holy malt is a serious problem or not.

So let’s get down to the nitty, gritty, nerdy science of it all. Some barley varieties, such as Copeland and Conrad, are especially desirable for malting due to their strong, resilient husks that provide some protection against kernel breakage during malthouse movements and bulk transportation. As a side effect of that extra husk strength, these same varieties can sometimes be pierced by their own acrospires as they grow in the germination compartment. Much like a stubborn flower that will eventually emerge through the sidewalk that resists its path of growth toward the sun, a growing acrospire will eventually pierce through a stubborn husk that refuses to budge. What results is a small, round hole in the dorsal side of the kernel. Figure 1A below shows this phenomenon in a sample of Copeland barley. Figure 1B shows the same kernel after it has been dried and the acrospire has fallen away. When this type of growth occurs, the flavor and function of the resulting malt kernel is unaffected and the quality is in no way compromised.

Figure 1A: Copeland malt kernels that have been pierced by the growth of their own acrospires during germination.
Figure 1A: Copeland malt kernels that have been pierced by the growth of their own acrospires during germination.
Figure 1B: Copeland malt kernel from Figure 1A that has been dried and cleaned.
Figure 1B: Copeland malt kernel from Figure 1A that has been dried and cleaned.
Figure 2: Weevil infestation in malt
Figure 2: Weevil infestation in malt.

Compare the images shown in Figures 1A and 1B to that of the weevil infestation shown in Figure 2. In this picture, you see that the adult weevil emergence holes are randomly placed and are affecting much of the grain. Even more importantly, the adult weevils can be seen as they remain to feed on the grain.

When holes are observed in malt kernels, suspicions should indeed be raised. However, careful observation will reveal the true culprit. If holes are observed randomly throughout many of the kernels and insects are present, this is a very serious issue and customers are advised to keep the infested malt sealed and separated and to contact their pest control agency and supplier immediately. Yet, if holes are observed in the dorsal side of some of the kernels, but insects are nowhere to be found, you can breathe a sigh of relief. These types of holes are not a sign of weevil infestation, but rather the result of a very determined acrospire overcoming a strong, stubborn husk.