Sample Analysis by Membrane Filtration

Membrane filtration is a highly sensitive method used in microbiology to detect low levels of microbial contaminants, including bacteria, wild yeasts, and molds. In this technique, a measured volume of liquid (typically 100–1000 mL) is passed through a sterile membrane filter (0.45 µm or 0.22 µm pore size), which traps microorganisms. The filter is then placed onto selective agar media, such as HLP, MRS, or WL Nutrient Agar, and incubated under appropriate conditions. After incubation, colonies are examined for identification and enumeration. This method is particularly effective for quality control in packaged beer, as it can detect even trace amounts of spoilage organisms that may affect product stability.