20.500.12556/DKUM-84254 Določanje sprememb v kemijski sestavi hmelja pri različnih pogojih skladiščenja ter vrednotenje vpliva postaranega hmelja na aromo in grenčico piva doktorska disertacija Determination of changes in hop chemical composition under different storage conditions and evaluation of the effect of aged hops on the aroma and bitterness of beer Hmelj (Humulus lupulus L.) je dvodomna trajnica, ki obrodi enkrat letno, njegova uporaba, ki je omejena predvsem na pivovarsko industrijo, pa poteka skozi celotno leto. Zaradi navedenega je uporaba svežega hmelja skozi leto praktično nemogoča, zato je izjemnega pomena ohraniti kakovost hmelja na kar se da visoki ravni. V sklopu doktorske disertacije smo ovrednotili vpliv različnih pogojev skladiščenja (anaerobno/aerobno, 4 °C/sobna T) na vsebnost alfa-kislin, beta-kislin, eteričnega olja, komponent eteričnega olja in na vrednost HSI-ja, v šestih različnih sortah (Celeia, Aurora, Bobek, Styrian Gold, Savinjski golding in Styrian Wolf), v obliki storžkov in peletov. Navedene parametre smo spremljali dve leti, s čimer smo objavili prve tako obširne in dolgo trajajoče študije o stabilnosti hmelja pod različnimi pogoji na svetu. Prav tako smo s poskusom varjenja piva preučili vpliv postaranega hmelja na kakovost in intenzivnost arome ter grenčice piva in tudi tukaj objavili eno prvih raziskav na področju vpliva postaranega hmelja na kakovost piva. Vsebnost alfa- in beta-kislin, vsebnost eteričnega olja, sestavo eteričnega olja, grenčico in HSI smo analizirali po že vpeljanih metodah, za analizo hmeljne arome piva ter vsebnosti humulinonov in izo-alfa-kislin pa smo vpeljali nove analizne metode. Validacija navedenih metod je predstavljena v sklopu doktorske disertacije. Pri preučevanju vplivov skladiščenja smo ugotovili, da s pogoji skladiščenja vplivamo na kakovost hmelja, ter da s primernim skladiščenjem upočasnimo procese staranja. Za najprimernejše so se izkazali anaerobni pogoji pri nizkih temperaturah (4 °C), za najmanj primerne pa aerobni pogoji pri sobni temperaturi. Pri beta-kislinah in HSI-ju je na njuno vsebnost vplivala tudi oblika hmelja, peleti so se izkazali za obstojnejše. Odstotek vsebnosti n-humulona v alfa-kislinah se skozi skladiščenje ni spreminjal, se je pa spreminjala vsebnost n-lupulona v beta-kislinah v peletih. Razmerje med alfa- in beta-kislinami je pri neoptimalnih pogojih skladiščenja v storžkih naraščalo, v peletih pa se je nižalo. HSI je z naraščanjem časa eksperimenta naraščal, s čimer smo potrdili naraščanje oksidacijskih produktov alfa- in beta-kislin. Naraščanje oksidacijskih produktov se je odražalo tudi v pivu; višji kot je bil HSI hmelja uporabljenega za pripravo piva, nižja je bila kakovost piva. Pri hladno hmeljenem pivu se je, z naraščanjem HSI-ja pri hmelju uporabljenemu za hmeljenje, zniževala intenzivnost in kakovost arome, prav tako vsebnost komponent eteričnega olja. Zniževala se je tudi kakovost grenčice, pri uporabi hmelja s HSI-jem višjim od 0,6 pa smo zaznali prekomerno penjenje. Pri tradicionalnem postopku hmeljenja postaran hmelj manj vpliva na samo kakovost piva, sploh kadar imamo dolg čas vrenja hmelja. Se pa predvsem na aromi zazna prisotnost oksidacijskih produktov, ki v pivo vnesejo vonj po postaranem in oksigeniranem. Na podlagi rezultatov smo tako postavili mejo za kakovosten hmelj, ki ne vpliva negativno na aromo in grenčico piva. Pri hladnem hmeljenju je ta meja 0,4 pri Aurori in Celei ter 0,5 pri Styrian Wolfu, pri tradicionalnem hmeljenju pa je ta meja 0,5. Doktorsko delo tako predstavlja obsežen vpogled v spremembe kemijske sestave pri različnih načinih skladiščenja in spremembe na aromi in grenčici piva pripravljenega s postaranim hmeljem. Hop (Humulus lupulus L.) is a dioecious perennial plant that produces a crop once a year, with their usage primarily limited to the brewing industry. Due to this, the use of fresh hops throughout the year is practically impossible, making it extremely important to maintain the quality of hops at the highest possible level. In this doctoral dissertation, the impact of different storage conditions (anaerobic/aerobic, 4°C/room T) on the content of alpha-acids, beta-acids, essential oil, essential oil components, and HSI (Hop Storage Index) was evaluated in six different hop varieties (Celeia, Aurora, Bobek, Styrian Gold, Savinjski golding, and Styrian Wolf) in the form of cones and pellets. These parameters were monitored for two years, resulting in one of the most comprehensive and longest-lasting studies on hop stability under different conditions in the world. Furthermore, the influence of aged hops on the quality and intensity of beer aroma and bitterness was studied through a beer brewing experiment, resulting in one of the first studies on the effects of aged hops on beer quality. The content of alpha and beta-acids, essential oil, essential oil composition, bitterness, and HSI were analyzed using established methods. New methods were introduced for analyzing hop aroma in beer and the content of humulinones and iso-alpha-acids, and the validation of these methods is presented in this dissertation. The results show that storage conditions have a significant impact on the quality of hops, and suitable storage can slow down the aging process. Anaerobic conditions at low temperatures (4°C) were found to be the most appropriate, while aerobic conditions at room temperature were found to be the least suitable. The form of hops also had an impact on the content of beta-acids and HSI, with pellets being more stable. The percentage of n-humulone in alpha-acids did not change during storage, while the content of n-lupulone in beta-acids in pellets did. The ratio of alpha and beta-acids increased in cones under non-optimal storage conditions but decreased in pellets. The hop aging index increased with time, confirming the increase in oxidation products of alpha and beta-acids. The increase in oxidation products was also reflected in beer quality, with higher HSI hops resulting in lower beer quality. Dry hopping resulted in a decrease in the intensity and quality of aroma and the content of essential oil components as HSI increased. The quality of bitterness also decreased, and excessive foaming – gushing, was observed when hops with an HSI higher than 0.6 were used. In traditional hopping, aged hops had less of an impact on beer quality, especially with long boiling times. However, the presence of oxidation products was mainly detected in the aroma, giving the beer a smell of aged and oxidized hops. Based on the results, a quality threshold for hops that does not have a negative impact on beer aroma and bitterness was established. This dissertation provides valuable insights into the effects of different storage conditions on hop quality and aging and their impact on beer quality. postaran hmelj kakovost piva alfa-kisline beta-kisline HSI eterično olje hmelja aged hops beer quality alpha-acids beta-acids hop essential oil HSI true true false [K. Rutnik] Slovenski jezik Angleški jezik Doktorsko delo/naloga 2023-05-09 11:29:38 2023-11-30 13:01:08 2023-12-05 03:13:19 0000-00-00 00:00:00 2023 0 Maribor 0 Maribor X, 129 str. 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 663.432:[66.89:631.563](043.3) 174750979 DOK_Rutnik_Ksenija_2023.pdf DOK_Rutnik_Ksenija_2023.pdf 1 F52BB8093673E97E0B9D55692FB6E2E3 3143e19d1d63bf677822354dced149530b22cd7c338ffdd4a0a3521fe3b1298f 8b96d445-83a1-11ee-b01c-00155d000105 https://dk.um.si/Dokument.php?lang=slv&id=174168 Fakulteta za kemijo in kemijsko tehnologijo 0 0 0