Application of quantitative nuclear magnetic resonance spectroscopy to biological acidification of barley mashes

Abstract

Spontaneous biological acidification has long been a part of the German brewing tradition, and was historically used to optimize the pH of brewhouse mashes. By facilitating the growth of native barley flora, the production of lactic, acetic and succinic acids sours the mash, functioning in a similar way to the addition of food-grade acids, which are prohibited under the Reinheitsgebot of 1516. Traditionally, sour mashes have been performed at the 'optimum' temperature of 49°C. Quantitative proton nuclear magnetic resonance spectroscopy was used for the investigation and quantitation of organic acids produced by acidified mashes over a range of temperatures. All target metabolites demonstrated an inverse relationship with temperature, although lactic acid reached a relative maximum at 49°C, which is in agreement with the customary sour mash temperature. Therefore, it would seem that the optimization of a sour mash is dependent not on absolute acid concentration, which would give the greatest pH regulation potential, but on the relative acid concentration, an important factor influencing the final flavour profile of a beer. © 2014 The Institute of Brewing & Distilling.