Influence of ohmic heating treatment on microbial growth, chemical-physical and organoleptic properties of beer

Beer quality and sensory characteristics can be affected by microbial spoilage. The shelf life of beer is often enhanced with thermal treatments in tunnel pasteurisers or plate heat exchangers. Ohmic or Joule heating can be used instead of traditional food processes: heat spreads out quickly and homogeneously into the product thus minimising sensorial properties decay. The aim of this study was to verify the effects of ohmic heating on the microbial growth and standard quality attributes (turbidity, chill-haze, colour, alcohol, CO2, pH, total polyphenols and sensorial properties) of 3 different beers: International Pale Lager, American IPA and Strong Belgian Ale. Also volatile aroma-active compounds were determined by HS-SPME-GC-MS. Beers for trials were brewed on 1 hL pilot plant, fermented and cold matured in 1 hL cylindro-conical vessels. Matured beers were heat treated at 28 PU using pilot scale Ohmic heater equipped with an aseptic packaging system. Untreated beers were kept as control. Results show the effectiveness of treatment to erase microbial population while a slight change on standard quality attributes was observed. In all beers turbidity and chill-haze increased in treated samples, whereas alcohol and CO2 content slightly decreased. Also, total polyphenols content showed a significant reduction, which appear more pronounced in IPA style beer. Despite the variability revealed by the instrumental analysis, sensory analysis of IPA and Strong Belgian Ale did not retrieve statistically significant differences between treated and untreated beer, while the panel was able to discriminate treated beer of International Pale Lager from untreated ones. This research shows that ohmic heating treatment is a suitable technology for biological beer stabilisation.