Iron Enhances the Growth of the Genus Pectinatus in Beer

Abstract To determine factors affecting the growth of the genus Pectinatus in beer, P. frisingensis ABBC437 was inoculated into 15 different beer samples. Although the pH, alcohol content, and bitterness unit of the 15 beer samples were adjusted to similar values within tolerance, growth kinetics as expressed by OD600 (optical density measured at a wavelength of 600 nm) were considerably different among the beer samples, indicating the presence of “as yet” unidentified factor(s) affecting the growth of P. frisingensis in beer. Chemical compositions of the beer samples were determined, and multiple regression analysis was conducted to predict the OD600 value. As a result, iron was suggested as one of the factors that affects the growth of P. frisingensis in beer because the additions of iron to the beer samples showed enhanced growth of P. frisingensis in a dose-dependent manner. Stimulatory effects of growth by the addition of iron were also observed for P. cerevisiiphilus and P. haikarae. Additionally, effects of diatomaceous earth treatment on the iron concentrations of the beer samples were evaluated. Iron concentrations varied, depending on the brand of diatomaceous earth, and the growth of P. frisingensis in beer showed a high correlation coefficient (0.924, p < 0.01) with the iron concentration in the beer samples. From these results, iron can be considered as an important factor for the growth of the genus Pectinatus in beer and selecting a low iron concentration diatomaceous earth is an effective way to improve the stability of beer against the risk of spoilage by the genus Pectinatus.