Permeability analysis of high-adjunct-ratio spent grain layer in the high-gravity wort separation process

• We designed an observing filter device for evaluating the filter medium.
• The particle property of adjuncts is key factor for the extension of lautering.
• The adjunct of corn starch results in dense, viscous and layered spent grain layer.
• The rice flour results in loose, polyporous and uniform spent grain layer.

High-adjunct-ratio beer brewing often encounters some problems like instable process of wort separation and fluctuation of lautering time, which greatly affects optimal brewery's capacity. In order to analyze the factors influencing the lautering process, which was derived from different adjuncts (corn starch and rice flour), the permeability of obtained spent grain layer (SGL) was evaluated using a designed observing filter device. The structure and particle distribution in the SGL were also analyzed. The results showed that the lautering time in high-adjunct-ratio brewing process was mainly dependent on the permeability of SGL other than wort viscosity. High proportion of corn starch caused a dense, viscous and layered SGL, and then reduced the permeability of SGL, but rice flour resulted in a loose, polyporous and uniform SGL and increased the permeability of SGL. The general blocking factor is proved to be the particle properties of adjunct. This study provides us a new and simple method for evaluating the permeability of SGL, but also helps brewer insight into the practical problem of lautering extension in high-adjunct wort separation process.