Extension of shelf life of commercial opaque beer using flash pasteurisation process Benias Nyamunda *2 , Ropafadzo Tshalibe 1 , Tecklah Usai 1 , Fortune Rwafa 1 1 Midlands State University, Department of Food Science, Private Bag 9055 Gweru, Zimbabwe. 2 Manicaland College of Applied Sciences, Department of Chemical and Processing Engineering, Fernhill Campus, Mutare, Zimbabwe. Corresponding Author email: nyamundab@gmail.com Abstract. The effects of flash pasteurisation of wort after second conversion stage were investigated with the intention of extending the shelf life of opaque beer from current 120 h. The extension of shelf life was determined by following the biochemical, physico-chemical and the sensory profile of the variants up to the point total acidity goes beyond the threshold of 0.5% v/v. The samples were subjected to wort flash pasteurisation for 120 seconds. Flash pasteurisation extended the shelf life of the beer from 120 h to 168 h. The physical, chemical and sensory attributes of the beer remained the same. Keywords: flash pasteurisation, malt, mashing, shelf life, opaque beer 1 Introduction Brewing of traditional opaque beer is a common practice among African societies. The brewing processes involve the blending of sorghum malt and meal, barley malt and straight run maize grits. Extraction and breakdown of carbohydrates from these raw materials to make a sugar solution and subsequent fermentation with yeast produce ethanol and carbon dioxide [1]. Brewing of opaque beer has been commercialised, currently the opaque beer industry is a well established and expanding [2]. In Zimbabwe there are at least 20 opaque beer breweries that produce over 420 million litres of the beer annually [1], [3]. Sorghum malt which is added during second conversion (mashing) stage in the brewing process of opaque beer has a high microbial load and is the major source of contamination [4], 5]. There is no further heat treatment or any other sterilisation process carried out after the second conversion that inhibits or eliminates the growth of the bacteria. Opaque beer is therefore sold as a microbiologically active and live product which is prone to spoilage as beneficial acid producing bacteria continue to grow even after acceptable levels of total acids have been attained [6], [7], [8], [9]. The short shelf life of opaque beer (120 hours) remains a big problem to the profitability of brewing opaque beer. Efforts have been made aiming at improving the shelf life of opaque beer. These include removing the second malt conversion stage, beer refrigeration and carbonation and substituting sorghum malt with commercial amylase enzyme, Alphalase [1], [10], [11]. However the high cost and infrastructural requirements of these preservation techniques greatly restrict their application in the extension of shelf life of opaque beer. The focus of this study therefore is to extend the shelf life of opaque beer brewed from a local commercial company (Pungwe Breweries, Mutare, Zimbabwe). Shelf life extension would be achieved through flash pasteurisation of wort after second conversion stage in the brewing process to reduce the load of acid producing bacteria in wort. The pasteurisation process is done prior to the second conversion stage. An additional pasteurisation process will not have significant additional costs to the entire brewing process. Pasteurisation is a heat treatment process applied to kill pathogenic bacteria and to significantly reduce the spoilage microbial load [12], 13]. Appropriate combination of temperature and time will minimise changes in the sensory (flavour, colour) and quality of the beer. The effects of flash pasteurisation on head retention, settling time, viscosity, pH, total acids, alcohol content of the opaque beer were investigated. 390 ACRID 2017, June 20-21, Victoria Falls, Zimbabwe Copyright © 2017 DOI 10.4108/eai.20-6-2017.2270763