# Using Hydrofluorocarbon Extracts of Hop in a Pilot Scale Brewing Process
## 3 Results and Discussion
Figure 4: Total iso-\(\alpha\)-acids concentration (ciso-\(\alpha\)-acids) evaluated during 50 min boiling when pellets, CO\({}_{2}\) extract, or HFC extract were added to the word during laboratory-scale isomerization trials. Figure 3: \(\alpha\)-acid concentration (c\({}_{\alpha\text{-acids}}\)) in the hop extract obtained during the HFC extraction process. In Figure 5, the isomerization yields, \(\eta_{\text{iso}}\), evaluated over the process time with sc-CO\({}_{2}\) and HFC extracts, were compared with the maximum isomerization efficiency of approximately 16.73%, reached by pellet addition (trial II) after 50 min of boiling. A maximum isomerization yield of 20.32% was achieved after 35 min of process using HFC extracts. This result could be further improved, as suggested by [PERSON] et al. [32], which studied the effect of optimizing pH, ionic strength, wort gravity, hopping rate, and metal ion catalysts on isomerization performances. Assuming as reference value the maximum amount of iso-\(\alpha\)-acids reached using traditional pellets (trial II), it was evident that both sc-CO\({}_{2}\) extract and HFC extract allowed the achievement of this value in shorter process times (approximately 34 min and 25 min, respectively) than those commonly used for the traditional process (50 min). As the addition of the HFC extract allowed to considerably reduce the treatment times, its implementation into a pilot-scale process was studied to confirm this behavior. Samples collected during the pilot-scale trial I4 showed lower iso-\(\alpha\)-acid concentrations than those measured in lab-scale withdrawals (trial I3), as shown in Figure 6.  
Figure 5: Isomerization yield, \(\eta_{\text{iso}}\), referred to the total \(\alpha\)-acid amount added to the wort by means of CO\({}_{2}\) and HFC extracts, at the beginning of the lab-scale isomerization trials. Horizontal line indicates the isomerization percentage reached after 50 min boiling by pellet addition. Figure 6: iso-\(\alpha\)-acid concentration (ciso-\(\alpha\)-acids) measured during isomerization trials performed at laboratory- (I3) and pilot-scale (I4) using HFC hop extracts. However, the same isomerization yield of approximately 9%, obtained after 50 min using the traditional procedure (hop pellets), was reached with the HFC system after a shorter time of about 35 min, as observed in Figure 7.  
It can be assumed that this discrepancy was essentially attributable to structural differences in the experimental systems used to conduct the laboratory- and pilot-scale tests. In both cases, the mixing was essentially due to natural convection phenomena. The different reactor geometry, the use of a completely different heat adduction system, and a greater liquid head in the pilot-scale apparatus affected the heat and mass transfer processes and allowed the presence of temperature and concentration gradients with a significant impact on the \(\alpha\)-acid solubility, influenced by pH and temperature [32], and the resulting isomerization performances. Therefore, less efficient agitation and wall adhesion conditions inside the pilot vessel could have negatively affected the conversion of \(\alpha\)-acids into iso-acids, leading to isomerization yields lower than those reached during the lab-scale experimentations. However, the isomerization kinetics resulted to be higher than those observed during the conventional boiling with pellets.