The effects of grinding (medium-coarse) and extraction time (14–22 h) on the physicochemical and sensorial properties of cold brew coffee produced using two types of Colombian specialty coffees (Huila and Nariño) were evaluated. Cold coffee brewed under coarse grinding and 22 h of extraction exhibited the highest values of total dissolved solids, extraction yield, pH, titratable acidity (TA), and total phenolic content. The type of coffee used mainly affected the TA and pH. All cold brew coffee samples had lower TA values than their hot counterparts. Nariño cold brew samples had higher TA values than those of Huila in all treatments evaluated. Higher scores were reported in the sensorial evaluation of cold brew coffee when prepared using the shortest time (14 h) and coarse grinding for both coffee types. These coffees were characterized by strong sweetness, fruity and floral flavours, medium bitterness and acidity, and a creamy body. Furans, pyrazines, ketones, aldehydes, pyrroles, esters, lactones, furanones, and phenols were detected as odour-active compounds. The findings of this study demonstrate that the particle size, contact time, and coffee type affect the physicochemical and sensorial characteristics of cold brew coffee, leading to cold brew coffees with different flavour profiles.

In conventional processes, such as evaporation, higher levels of concentration can be reached compared with freeze concentration or membrane techniques. However, the advantage of the freeze concentration technique is based on the quality of the product obtained due to the low temperatures used in the process, which makes it a very suitable technology for the processing of fruit juices. There are two basic methods for concentrating solutions by freezing: suspension and film freeze concentration. Suspension freeze concentration systems (FCS) already have operating equipment in the food industry, while film FCSs, also called layer crystallization, is still at an experimental stage. This review summarizes the most important studies relating to the suspension and film freeze concentration in fruit juices and sugar solutions, illustrating the different possibilities that freeze concentration has in the fruit juices industry; it also presents trends and suggests improvements for the future development of this technology. It is noted that most recent publications refer to the film FCS. The technology used to design, build and maintain layer crystallization equipment is simple and it can be available to any operator in the food industry, layer systems will be used in the future if their results can be improved in terms of ice purity and degree of fluid concentration.

Coffee extract was freeze-concentrated using the total block technique. The effects of four parameters\ud were evaluated: the initial coffee mass fraction (5 and 15% w/w), the cooling temperature ( 10 and\ud 20 C), the heating temperature (20 and 40 C) and the freezing direction (parallel and counter-flow\ud to the thawing direction). The solid concentration was measured during the thawing stage to quantify\ud the solute recovery and the concentration index for one stage of freeze concentration. The coffee mass\ud fraction, the freezing direction and the cooling temperature significantly influenced the solute recovery.\ud A concentration index between 1 and 2.3 was obtained in one cycle. The effect of block freeze concentration\ud on the bioactive compound concentration and the antioxidant activity was measured. The coffee bioactive\ud compounds were distributed in proportion to the total solid content in the ice and liquid.\ud Therefore, block freeze concentration is an effective technique to preserve functional properties of coffee\ud extracts.Postprint (published version

Coffee extract was freeze-concentrated through block and falling-film techniques. Solute retention and\ud concentration efficiency were determined after one stage of these processes. Ice morphology was characterized\ud through image analysis. Preservation of volatile compounds was determined through GC–MS.\ud The effect of coffee extract on flavour was determined after freeze concentration through sensory evaluation.\ud Solute occlusion was higher for falling-film than for block freeze-concentration, with an average\ud distribution coefficient of 0.45 and 0.29, respectively. The ice crystal size was lower for the falling-film\ud technique; this explains the higher solute occlusion. The dewatering capacity was higher for the\ud falling-film technique, as this process is faster than block freeze-concentration. The most abundant volatile\ud compounds of the coffee extracts were preserved after freeze concentration with both techniques. In\ud the same way, no differences were found in most of the sensory attributes of the freeze-concentrated\ud extract obtained using both techniques. Our results confirm the benefits of the block and falling-film\ud freeze concentration techniques in preserving the quality of coffee extracts.Postprint (author's final draft