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An Expert View: Denis De Keukeleire, the Hoppy Professor

Denis De Keukeleire

GHENT/MELLE - “I am quite surprised that the hop is surrounded by so much hype these days. It used to be just a commodity,” Ghent professor Denis De Keukeleire begins. No-one else is better placed to provide an analysis: he has been studying this climbing plant with its magical qualities for over 50 years.

This Belgian ‘hop professor’ is a jack of all trades: a chemistry graduate, a visiting professor at Brazil’s Sao Paulo University, zythology teacher, author, media personality… He has even investigated the impact of light on beer, at the California Institute of Technology, and has given over 750 lectures in 43 countries, and the meter is still running.

Denis De Keukeleire is known around the world for his authoritative views on and knowledge of the make-up and uses of hops. Its use in beer springs easily to mind, but there are also medical uses for this wonderful plant.

For example, Denis contributed to the development of a hop-based medicine to treat Diabetes 2 and also worked on a hop food supplement to regulate the effects of hormones in menopausal women. “How did it all start? I discovered beer culture during my student days in Ghent,” he laughs. “On Saturdays we often had cantuses [sing-alongs] and dances accompanied by a live orchestra. The beer flowed freely. Hard times!”

Denis De Keukeleire, Hops in Belgium

A Magic Plant

Ghent University started researching the hop plant in 1949 with the support of the then largest brewery in Ghent, Excelsior. The focus at the time was on the Saaz hop, a mild variety that is often used in pilsners.

Before then the emphasis of research was usually on the possible medical uses of hops. The professor is now further examining its healing properties: related to hemp – from which cannabis comes - it has a narcotic effect and also produces the female oestrogen hormone known as "hopeine".

The professor’s class continues: “The hop is a fascinating plant. Did you know that lupuline, a substance extracted from hops and required for beer brewing, contains around 300 substances? It is an important bioreactor. In just 14 days, the inside of the hop flower can produce it as a powder that is really a concentrat/e of protective agents.

This genetically-determined survival mechanism allows the plant to combat viruses, bacteria, moulds, UV-rays… The more noxious the environment, the more effective the mechanism. The weight of the lupuline represents one-third of the dry weight of the hop cone or flower, a record in the realm of the plants!”

Lupuline contains bittering agents which give the distinctive taste, polyphenols to help the plant survive and essential oils that determine the aroma and also protect the plant from bacteria. The proportion of these elements varies from variety to variety and can also be changed by the growing environment.

There are now more than 200 hop varieties. Bitter hops contain between 10 and 25% of the bittering agents; in aroma hops there will be 5% at the most. The so-called ‘double target hop’ varieties combine the best of both worlds: they have the 10% or more of bittering agents of the bitter hop but also have a highly-valued aroma.

Denis Dekeukeleire

Hop Hype

Hop shoots are keenly consumed in restaurants. However, they are not a vegetable, as we are about to find out. “The shoots have a very low nutritional value. All the good stuff is contained in the lupuline and the brewing process uses up all the nutrients,” the professor says.

“Brewers are after bitterness and aromas first and foremost. And polyphenols [complex compounds that help produce the bitter flavour] can also be found in malt.” Hops used to be a commodity. The brewer placed his order with his hop supplier and that was it.

But Times have changed. Heavily-hopped IPA’s (India Pale Ales) have conquered the world and dry hopping and exotic aroma hops are increasingly popular. In the USA alone, the proportion of agricultural land on which hops are grown has increased by 17%.

Many breweries are now using between four and 10 times as many hops as they used to in their quest to make veritable ‘hop bombs’ of their beers.

This has led to a hop shortage and therefore, prices are rocketing. Also, the highly-desirable aroma hops are more disease-prone and so the yield per hectare is lower than for the traditional bitter hops.

Denis De Keukeleire, Hops in Belgium

This hop hype has its own dangers according to the professor. “It’s quite complicated. If you are working with a single variety of hop, you can control the process,” he explains. “But if you are using different varieties of hops, the end result will be more complex and this may be at the detriment of taste."

"For example, the bitterness is reduced by the fruity flavours added; resulting in a more uniform beer, but you may end up with a beer that tastes predominantly of lemon or grapefruit.”

We need a 'hop-o-meter' to define all these varieties of hop. It would show that Saaz, Amarillo and Cascade have a balanced composition whereas the Citra, for example, has strong citrus fruit flavours. The brewer must consider all this when designing his – umpteenth – beer. It might be best to give the professor a call?

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