Projects / Programmes source: ARIS

Study of effects of hop aging on beer characteristics

Research activity

Code Science Field Subfield
4.03.07  Biotechnical sciences  Plant production  Technology of vegetal origin food 

Code Science Field
4.01  Agricultural and Veterinary Sciences  Agriculture, Forestry and Fisheries 
Hop, essential oil, alpha-beta acids, hop storage index (HSI), high pressure liquid chromatography, gas chromatography, DPPH, NMR, mass spectrometry
Evaluation (rules)
source: COBISS
Researchers (1)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  37419  PhD Miha Ocvirk  Plant production  Head  2020 - 2022  177 
Organisations (1)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0416  Slovenian Institute of Hop Research and Brewing  Žalec  5051762000  4,259 
Hops are an irreplaceable raw materials used in brewing process that decisively affects the aroma and stability of beer. The carriers of the bitter taste are hop’s soft resins (alpha acids). Depending on its composition, the hop's essential oil gives the beer its unique aroma, while the polyphenols in hops affect the astringent, foam stability and they also play an important role in maintaining the stable aroma of the beer during aging. In addition to the classic quality parameters of hops, which mainly reflect the quantity and composition of bitter substances and essential oils, the so-called hop storage index is also important. The oxidation of hops leads to the formation of oxidised products of secondary metabolites. One of these are humulinones, which are similar to iso-alpha acids. It is a relatively new discovery with many things still to be explored. It is well known that a high quality beer flavour requires the synergy of a large number of hops essential oils and bitter substances. If of the components prevail, is dominant or in deficit, this equilibrium can be broken and the results are quickly detected by the consumers. Oxidation, decomposition of alpha acids and essential oil components, or even reaction between particular compounds can lead to the appearance of a number of undesirable products, so called off-flavours. We will prepare hop samples which will be stored in different conditions, commonly used in praxis. We will prepare aluminium bags, with the absence of light and oxygen, which will represent the correct type of packaging. On the other hand, we will prepare hop samples (cones and pellets) in the bags with air present. Samples will be stored in cool places and on room temperature for two years. Special emphasis will be put on the monitoring of hop quality parameters during different types of storing conditions after time (WP1). In WP2, hops with different concentrations of copper will be aged under the same conditions. With measuring HSI and antioxidant activity (DPPH) we will find a link between the influence of copper concentrations in hop samples and dynamics of aging and the formation of oxidation products. In WP3, we will prepare experimental beers in our experimental brewery, using properly and improperly stored samples. We will use the same batch of wort divided into two equal sizes for later kettle hopping, to avoid differences originating from malt and amount of hops. At our institute, we have all necessary equipment and knowledge for determination of physical – chemical properties of beer. In WP4, we will collect beers, brewed with our stored hop samples, and evaluate them during standard sensory evaluation on beer aroma, odor and bitterness. In this part, we will also try to found or detect any off-flavours originating from improperly stored hop samples compared to properly stored samples. In WP5, we will develop analytical methodology for monitoring and identification of, until now, unknown hop aging products and their reaction products. The characterisation and influence of the individual parameters between different hop aging methods will contribute significantly to the evaluation of hop brewing value. Studying the consequences of brewing beer with the use of hops with different HSI will mean advances in the knowledge of hop chemistry in brewing. The study of alpha-acid degradation products during aging is a relatively unknown area and opens up numerous possibilities for research with various analytical techniques. Using NMR spectroscopy, would allow us the qualitative and quantitative determination of the decomposition products of alpha acids and essential oil components. We will also use the DPPH method, with this method we will found out, how choosing the right packaging affects on the presence of antioxidants that protect molecules from aging. The results of the research will make an original contribution to the knowledge of the possibilities offered in the brewing and hops area.
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