The Influence of the Withering Temperature on the Resulting Proteolytic and Cytolytic

Abstract

During kilning, the germinated malt has to be dried from moisture contents of 42–48 to 3–6 % to interrupt the growth and to make the malt storable. Therefore, the green malt is firstly dried by blowing air with moderate temperatures between 45–65 °C through the grain bed. This first of two steps during kilning is called withering and it is important to ensure highest possible enzyme activities in the malt which are mandatory for later brewing process. During withering, the enzyme formation and activities are accelerated and a lot of biochemical reactions, e.g. the enzymatic degradation of cell wall substances hemicelluloses (cytolysis) and protein (proteolysis), occur especially at a stage of still high grain's moisture content. The withering temperature has a remarkable influence on the final malt quality. After withering, when a moisture content of 10–15 % is reached, the malt is cured at higher temperatures between 75–90 °C for some hours for pale malt like Pilsener malt. 

Laboratory withering trials in a grain layer height of 35 cm applying isotherm temperatures between 30 and 60 °C were carried out to investigate the influence on the resulting pale malt quality especially by means of the cytolytic and proteolytic modification. The curing process, 4 hours at 80 °C, was kept constant for all trials. The cytolysis was enhanced by reducing the withering temperature. Comparing the 30 and 60 °C samples, an about 60 mg/L lower β-glucan content, an about 8 % higher mealiness and an about 5 % higher modification according to Carlsberg could be observed. The proteolysis could be reduced as indicated by a 2.8 % lower Kolbach-Index comparing the lowest and the highest applied withering temperatures of 30 and 60 °C. Therefore, an optimal withering temperature regarding the cytolytic and proteolytic modification in present study was found to range between 30 and 37 °C. Additionally, the influence of the withering temperature on different layers of the grain bed was investigated. The upper layer stayed moist for a longer period, thus enzymatic activities, by means of a higher cytolytic and proteolytic modification, could take place in a higher extend. Thereby, the malt quality deviation between the upper and lower layer increased with higher temperatures. The disadvantages of lower withering temperatures are an extended kilning process and a slightly higher energy consumption of the kilning fan.