Hop Topic: Gland Profiling
Are your glands up?
Hopefully, your glands are fine. We’re talking about gland profiling, which helps our Farm Managers ascertain the essential oil content in our hops, so you guys get the best result in your beers.
Our shift in production to a focus on flavour and aroma has meant a change in how we determine the best time to harvest. Essential oil content is critical to the potency and impact our hops have in beer. Of course, this isn’t the only factor determining the best harvest time. The flavour potential of hops can be significantly influenced by maturity at harvest, and we’d like to show you a little bit about how we determine when the time is just right.
In the weeks before harvest, hop cone weight, dry matter and alpha acid are monitored. Dry matter is typically between 22 – 26% when maximum values for cone weight and alpha acid content are reached. Previously, we’d use these figures to determine an ideal target date for harvest, but we’ve found that essential oil content continues to increase in the days after alpha acid has peaked, so being patient really does pay off in the long run. To show you what all of this is about, we’ve included a graph from our 2013 Cascade harvest with observations of gland fill increasing after alpha content has stabilised.
To make sure we’re on point, we conduct visual profiling of lupulin glands in all commercially grown varieties on HPA farms in the days leading up to harvest. Based on this method, statistics show there has been a variety-dependent increase in essential oil content of around 0.2ml/100g in aroma varieties, peaking at a 0.9ml/100g increase; greatly affecting the flavouring potential in the hops you love.
The lupulin glands are concentrated on the bracts of the cones, accumulating a complex suite of plant secondary metabolites. For the scientists out there ‘essential oil’ contains a mix of hydrocarbons (monoterpenes such as myrcene, sesquiterpenes such as humulene), oxygenated compounds (terpene alcohols such as linalool), as well as other alcohols, ketones, esters and sulphur containing compounds.
The ways by which flavour active compounds are transmitted from hop to beer are diverse and complex, depending upon things like timing of hop additions and dosing, malt, yeast, filtration and the inherent quality of the product.
Ultimately, gland profiling helps us deliver you – the brewers and beer lovers – hops with great flavour and aroma potential. The rest is up to you!