Study of the super dry hopping technology by designing surface response models and sensory analyses

Dry hopping technology consists of the hop addition during the cold sides of the brewing process and it has gained much interest with the success of dry hopped beer,especially in America. However, some challenges still have to be overcome. Modern dry hopping techniques already exist but present some disadvantages (expensive facilities, reproducibility, extract losses, etc) and are not fully understood (transfer rate, flavour stability, etc). This work aimed to develop knowledge around dry hopping and to elaborate an effective dry hopping technique which fulfills the challenges, firstly at laboratory scale. The super dry hopping method consisting in the hop addition into a small external vessel completely offline and containing beer or process water has been selected as a promising technique. Impacts of pH, ABV and temperature on hop compound extraction into water process as solvent have been studied and response surface models have been designed. Thanks to those models, most significant terms for the dissolutions of specific hop compounds have been highlighted and optimal conditions can be determined. Regarding the dry hopping process, aromatic markers linalool and geraniol are of a great interest. Their dissolution is enhanced at either low (2) or high (7.5) pH, high ABV (up to 15% tested) while temperature effect was weak. The super extracts produced at low pH will also retain a certain amount of xanthohumol and Sconjugates while a higher pH improves greatly the dissolution of humulinones and alpha-acids. Therefore, a change of pH enables to separate hop resins from other hop compounds, which is interesting since alpha-acids and humulinones are usually unwanted or not useful during the super dry hopping process. In addition to analytical analyses, sensory trainings allowed to characterize the organoleptic impact of such extracts on a final beer. Despite the different extraction conditions tested, usually only subtle differences could be perceived between beer prototypes. Moreover, all prototypes were less intense in therm of hop flavours compared to the reference. Actually, a saturation point is reached at 25 g of hop/L of beer or process water during the super dry hopping process. Furthermore, the transfer rates of quantified hop compounds were usually much smaller than 100%, confirming the fact that hops remaining after a first extraction still contains a certain amount of valuable compounds. Sequential extractions are suggested to recover a fraction of those components. This strategy is especially relevant if extractions are performed in different conditions. It would lead to the production of two different extracts whose chemical composition largely varies as well as their impact on the resulting beer. Although the super dry hopping process is not so efficient than expected compared to the classic dry hopping at laboratory scale, some tracks exist to overcome the lack of hop aroma intensity of the resulting beers (sequential extractions or the decrease of the hop dosage). Moreover, such technique should be tested in the future at semi-industrial scale and with an action of the yeasts, which are both impacting the super dry hopping process.