Citrus, grapefruit, toffee, spice, apple, pear, biscuit, caramel… the list of flavors and aromas associated with beer is vast but how are they produced during the brewing process? The hop variety used in the brewing process is responsible for the bitterness, aroma, and flavor characteristics. These compounds can be extracted from hops by steam distillation, liquid-liquid extraction and analyzed using GC-MS.
John Langley and Julie Herniman (University of Southampton) run an undergraduate laboratory experiment extracting aroma compounds from hops. This advanced practical was designed to extend practical knowledge and experience, particularly in the field of analytical chemistry. The students are required to deliver laboratory notes, a 'Report for the Chief Brewer' and a poster. Their work is assessed for technical understanding, and uncertainties and errors associated with the whole practical and processing of their
The students undertake the extraction, sample submission and analysis, and have access to CHROMacademy to help them answer specific and general questions posed during the experiment.
The history of beer making goes back over 6000 years, whilst hops were introduced into this process around 1200 years ago. Malt was first used in the middle 17th century and the beers we recognize today are a product of the Free Mash Tun Act (1880) where the tax on malt was replaced by a tax on sugar. The new law then enabled "the brewer to brew from what he pleases and have a perfect choice of his materials and methods".
There are 20 commercially grown British Aroma Hop varieties in the UK. The British Hop aromas include notes such as tangerine, citrus, grass, grapefruit, chocolate, blackcurrant, spice, pepper, apricot, marmalade, and mint.1 Hops are the female flowers (also called seed cones or strobiles) of the hop plant, humulus lupulus (Figure 1). A hop cone consists of layers of soft tissue petals, within which lupulin glands form (these look like large yellow pollen grains). It is the lupulin glands that contain the oil resins which provide the bitterness, preservative properties, flavor, and aromas to beer.
Figure 1: Hops