THE CONTINUOUS BREWING OF BEER
Beer is produced commercially by the controlled fermentation of wort, a liquid rich in sugars, nitrogenous compounds, sulphur compounds and trace elements extracted from malted barley. Fermentation is the process by which glucose is converted to ethanol and carbon dioxide and is expressed chemically as: C6H12O6 + 2PO43- + 2ADP → 2C2H5OH + 2CO2 + 2ATP Behind this simplified chemical reaction is a series of complex biochemical reactions. These reactions (known as the ‘Glycolytic pathway’ or ‘Embden-Myerhof-Parnas pathway’) involve a number of enzymes and the reactions take place anaerobically inside the cells of brewing yeast. DB Breweries carry out this fermentation by a continuous process in which the beer moves through a series of stirred vessels for a period of 40 to 120 hours. After the ethanol has formed the beer is transferred to maturation vessels the flavour is naturally refined. Following this the product is developed into a variety of different brands. Breweries across the world generally use the system of batch fermentation to produce beer, it is the writer’s belief that at this time, only DB Breweries in New Zealand is successfully using continuous fermentation to produce full strength beers. INTRODUCTION Brewing has been mentioned in history as early as Egyptian times and has continued on to the present day with relatively few changes to the basic recipe. Malted barley is the main ingredient, which, when milled and heated in water to extract its nutrients, provides a nourishing sugar- and protein-rich solution named wort (pronounced wert), an ideal medium in which yeast may grow and ferment. In comparatively recent times hops were added to the boiling wort as it was discovered that hops had anti-bacterial properties which preserved the wort and fermented beer and which gave the beer a refreshing bitter taste. For many years the only known method of fermenting beer was a slow batch fermentation process carried out in a single fermentation vessel. This method had disadvantages in economic and quality aspects. The slow fermentation times meant that large numbers of tanks were required to house all the fermenting batches of beer (high costs of vessels and the associated costs for holding these vessels at the required temperatures and testing the quality of each batch). In addition, there was no guarantee that the beer would have a consistent flavour, something which is particularly important in these times of quality awareness. In the late 1950’s Morton Coutts of Dominion Breweries (now DB Breweries) introduced the concept of continuous fermentation (CF) and won international acclaim in the brewing world. Continuous fermentation involves recycling part of the fermented beer back to the wort at the start of the fermentation process and requires a continuous supply of wort into the system. The result is a continuous flow of beer out the other end of the process. Whereas in a batch fermentation system wort will be brewed then cooled to fermentation temperature then pitched with yeast and fermented, the wort brewing stage in a continuous system may be carried out at a time appropriate for the brewery (eg brewing may be organised to allow maximum power usage at off-peak times, or may be carried out around the clock for several VI-Food-A-Beer-1
days and then a period with no brewing to allow plant maintenance, shut-down for holiday period etc). Continuous fermentation employs a system of cold wort storage; the boiled wort is chilled to 0 C (the wort does not freeze at this temperature because of its high sugar content) and held in storage tanks where protein material (which would otherwise make the beer appear cloudy or ‘hazy’) precipitates out. The wort remains in the storage vessel until it is required to be steadily transferred to the fermentation. One wort storage tank will continuously feed into the fermentation for several days.
THE CONTINUOUS FERMENTATION PROCESS The...
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