Preparation of coffee beverage can be done in many different ways, such as decoction (e.g., boiled coffee, Turkish coffee, percolator coffee), infusion (e.g., filtered and napoletana coffee), and pressure (e.g., press pot, mocha, and espresso coffee)7.
Percolating is a method of coffee brewing by circulating a stream of boiling or nearly boiling coffee solution from the reservoir at the base, up through a central vertical pipe to the top of ground coffee bed. The coffee solution will be flowing continuously until the required concentration of the extract is achieved5. A desludging decanter could be installed as well, to recover some of the coffee solids from the discharged sediments obtained and to maximise the extraction yield2.
The aqueous extract is then allowed to cool and undergo a filtration step that is performed by using either centrifugal separators or filters to remove any insoluble pieces of the coffee beans, that could possibly have passed through the extraction column filters or any other unwanted insoluble particles formed inside the percolators. The extract is called clarified extract2.
In coffee, there is only a small percentage of volatile compounds, responsible for its typical aroma perception. After the extraction process, the flavours and aroma compounds tends to be lower than in the original ground roasted coffee2. Coffee aroma components can be concentrated and recovered in a two-stage condenser or distillation system by processing the extract at temperatures of 100°C to obtain the natural fresh brewed flavours4,8.
For beverage products, the primary goal of processing is to produce a safe and shelf life stable products by the means of eliminating pathogens and greatly reducing or eliminating spoilage bacteria11. The key unit operations to inactivate microbial activity in ready-to drink coffee drinks are pasteurization and sterilization6.
Pasteurisation is the gentlest heat process that is capable to greatly reduce microbial loads, but it needs to be combined with refrigeration to extend shelf life. The U.S. Food and Drug Administration requirement for pasteurisation is at least 160°F (71°C) for 6 seconds10 while hot filling and retorting sterilises the products and allows it to be shelf-stable for a year or more at room temperature. Other heat treatment includes aseptic, ultra-high temperature (UHT), and extended shelf life (ESL)11.
High-pressure processing (HPP) is also known as non-thermal pasteurisation. It applies high pressure of 400 to 600 mPA for 1-10 minutes, thereby reducing several log cycles of spoilage microorganisms and pathogens11. Without heat treatment, HPP is able to preserve sensory, nutritional and functional properties, especially in maintaining delicate aroma and flavour of coffee, as well as their bioactive compounds. HPP also extends the overall shelf stable period, from three weeks to three months or longer in refrigeration9.
The composition of the final beverage will depend not only on the brewing method, but also the degree of coffee grinding, powder to water ratio, water temperature, time of extraction and also types of coffee species that are being used to prepare the commercial blend3.
References
1Alfa Laval. (n. d.). A Clear Advantage In Beverage Processing: The Clara Disc Stack Separator Range. Lund, Sweden: Author.
2Farah, A. (2019). Coffee: Production, Quality and Chemistry (pp. 299-300). London: Royal Society of Chemistry.
3Galanakis, C. (2017). Handbook of coffee processing by-products: Sustainable Applications (pp. 8-9). Amsterdam: Academic Press.
4GEA Group. (n.d.). GEA process technologies for the instant coffee industry. Düsseldorf, Germany: Author.
5Ingham, J., Dunn, I., Heinzle, E., Prenosil, J., & Snape, J. (2008). Chemical engineering dynamics (3rd ed., pp. 8-9). Weinheim: John Wiley & Sons.
6Kilcast, D. & Subramaniam, P. (2011). Food and beverage stability and shelf life. Cambridge: Woodhead Publishing Limited.
7Petracco, M. (2008). Technology IV: Beverage Preparation: Brewing Trends for the New Millennium. Coffee: Recent Developments, 140-164. https://doi.org/10.1002/9780470690499.ch7
8Skaliotis, L. (2012). Beverage Applications using Spinning Cone Technology. Food Marketing and technology, 26-28.
9True Fresh HPP & Fulfillment. (2017). Cold Brew Coffee. Buena Park, California: Author.
10US FDA. (2018). Guidance for Industry: Juice HACCP Hazards and Controls Guidance First Edition.
11Zemser, R. (2015). The Changing Face of Beverage Processing. The World of Food Ingredients, 10-15.
