P-24 - Improving the Flavor Quality of Beer with Complex Sourness and Aroma

The creation of distinctive beers by microbreweries has recently become a trend in Japan. Customers want to choose a beer that suits their tastes. Therefore, breweries are expanding their ranges and varieties of beer flavors. In this study, we are working on developing a beer that is well-balanced with complex sourness and rich ripe-fruit-like aroma. We identified the key components responsible for these characteristics: acetic and lactic acids for the sourness and ethyl acetate for the aroma; these results were reported at a brewing summit in 2022. We continued to study beer quality, identified ethyl lactate as a new key component responsible for the rich ripe-fruit-like aroma, and confirmed that beer quality can be improved by increasing the ethyl lactate concentration to over 150 ppm, similar to the ethyl acetate concentration.  Therefore, we investigated a method for producing beer with high ethyl lactate concentrations. We previously found that Brettanomyces are important for the production of ethyl acetate. We hypothesized that ethyl lactate could be produced similarly to ethyl acetate because both are classified as ethyl esters. We investigated a method for increasing the ethyl acetate production capacity via Brettanomyces fermentation. However, the amount of ethyl lactate produced was only one-half to one-third of the target level, even when the fermentation conditions and Brettanomyces strains were controlled. As such, the new control factors that increase ethyl lactate production need to be identified. We thus focused on pH. We aimed to control the chemical esterification reaction caused by undissociated lactic acid through controlling the pH to be lower than the acid dissociation constant of lactic acid (pH 3.8). We proved that the production rate of ethyl lactate can be controlled by the pH of beer and its amount can be enhanced to the same level as that of ethyl acetate by adjusting the pH ranges from 3.3 to 3.0. Consequently, the ripe-fruit-like aroma of the resulting beer increased. In the future, we will explore key components other than those examined in this study and develop a method for their control.