Whey originates from microbial fermentation processes such as cheese and casein manufacture and is loaded with microorganisms from those operations. Thermalization is used to reduce bacterial numbers in whey before processing, however, bacteria that survive this are able grow within the manufacturing plant and contaminate the product. In hot processing plants, the growth of thermotolerant bacteria such as Streptococcus thermophilus can reach high levels on manufacturing plant surfaces blocking ultrafiltration modules. The current cold UF systems operating at 10°C solved that problem, however we are still facing microbial quality issues. Scrapings from ultrafiltration membranes reveal a variety of bacteria – many of which cannot survive thermalization and are hypothesized to enter via the water used for dialysis or cleaning. Control of water quality is therefore important. One problem that persists in today’s whey manufacturing plants is the growth of spore-forming bacteria that survive thermalization. Bacillus licheniformis is a common contaminant which we assume originates from raw milk but propagates as biofilm on manufacturing plant surfaces. Although many strains cannot ferment lactose, they grow readily on stainless steel surfaces in the presence of whey. Their growth is limited to zones close to their optimum growth temperature of 37°C before whey concentration and dialysis as growth is influenced by ions and protein concentration. They produce spores and protease, potential problems in whey products. The challenge is to manipulate conditions to prevent biofilm growth of B. licheniformis in manufacturing plant.