# Using Hydrofluorocarbon Extracts of Hop in a Pilot Scale Brewing Process
## 1 Introduction
While the first technique requires high operative temperatures which could reduce the quality of the final extracts, organic solvents are toxic, flammable, require expensive safety measures, and always involve subsequent separation processes [10]. Moreover, the presence of solvent residues in the final products requires additional purification steps that are time-consuming and increase the total process cost [13]. In both cases, the real disadvantage is the alteration of the extract composition [14]. Supercritical CO\({}_{2}\) (sc-CO\({}_{2}\)) extraction represents an optimal alternative to traditional techniques; it uses a non-toxic solvent with high solvating power and is easily removable from both the extract and the exhausted matrix. The main features distinguishing CO\({}_{2}\) extracts from conventional extracts are the lack of traces of undesired organic solvents and the absence of expensive purification treatments. Moreover, it allows an improvement in the flexibility of the process parameters [15] and in-process selectivity, ensuring high extraction rates and extracts with high bitterness power [16; 17]. In particular, a relatively high recovery of volatile compounds is obtained at lower temperatures, whilst elevated pressures and temperatures favor the high recovery of bitter acids and resinous compounds [13]. Recently, several innovative extraction techniques have been proposed, such as microwave and ultrasound systems, to increase the extraction efficiency of bioactive compounds in hop cones using water, ethanol, and their mixture as food-grade solvents [18]. [PERSON] et al. [19] investigated the effectiveness of innovative ultrasound-assisted and high hydrostatic pressure extraction methods: the recovery of polyphenols and carotenoidsfrom hop and the antiradical capacity of the resulting extracts were evaluated and compared with those of conventional extractions. In this work, the use of novel hop extracts in brewing, obtained in short times without excessively high costs, was investigated. An innovative patented extraction process [20] using hydrofluorocarbon (HFC) Norflurane (1,1,1,2-tetrafluoro ethane) as a solvent in subcritical conditions was proposed. The properties of this refrigerant fluid as an extracting solvent for the treatment of vegetable matrices were already investigated; this compound guarantees the recovery of bioactive compounds, such as lycopene and other carotenoids [21], or value-added oils from wet or dried agri-food wastes, such as spent coffee grounds and waste bilberry seeds [22; 23]. Moreover, despite the high environmental impact due to its Global Warming Potential (GWP) value of 1400, its convenience in terms of safety, low risk, low toxicity, and low plant and operating costs was confirmed by [PERSON] et al. [24], which compared hydrofluorocarbon extraction techniques with traditional and sc-CO\({}_{2}\) processes. The problems linked to its contribution as a greenhouse gas can be significantly overcome by a closed extraction system in which the solvent is continuously regenerated and recirculated. Moreover, the use of hydrofluorocarbon solvents in subcritical conditions allows overcoming the need for a drying pre-treatment of the solid matrices [22] and the use of suitable co-solvents aimed at improving the recovery of polar molecules of interest [25], indispensable for other extraction techniques, including sc-CO\({}_{2}\) process. To verify the potential of this novel extraction process, the total extraction yield and \(\alpha\)-acid recovery were determined and compared with those reported in the literature and obtained with a supercritical CO\({}_{2}\) process. The kinetics of the \(\alpha\)-acid isomerization during boiling were investigated on a laboratory scale using hop pellets, commercial CO\({}_{2}\) extracts, and HFC extracts.