Bacteriophages in whey powder processing: Sources of contamination and control strategies

Background: Cheese production generates vast quantities of whey, often dried into whey powders for reuse. These whey powders can harbour bacteriophages that threaten starter culture performance and product quality. Aim and Scope: This review examines bacteriophage contamination in whey powder production and its impact on cheese fermentations. It discusses how phages enter and survive in whey and whey powder, identifies the sources of phage contamination and evaluates strategies to reduce phage dissemination via whey powders in cheese manufacturing. In addition, the survival of phages during whey processing and storage is also discussed. Method: A comprehensive analysis of recent literature and case studies was undertaken to assess the prevalence, effects and management of phage contamination in dairy production. The review synthesises data on whey production and phage characterisation, with emphasis on both industrial and artisanal practices. Major Findings: Phage contamination is a significant challenge in dairy fermentations, particularly when phage-contaminated whey or whey powders are recycled into new cheese production. Bacteriophages survive pasteurisation and even concentrate during whey evaporation and filtration, remaining viable in dried whey powders (with titres up to ~108 PFU/g observed). These phage-contaminated powders can reintroduce infection into fresh fermentations. A multi-hurdle approach, combining targeted nonthermal and moderate thermal interventions during whey processing, is recommended to inactivate thermo-resistant phages while preserving whey protein functionality. Scientific Implications: Understanding the diversity and mechanisms of phage–host interactions in the context of whey processing is crucial for the development of robust starter cultures and targeted phage-control strategies for safe whey powder production. This supports sustainable dairy manufacturing by enabling the safe reuse of whey as a high-value ingredient while preserving the functional and economic value of whey protein powders. Integrating phage-resistant starters, optimised process design and combined treatments is essential to minimise phage risk, ensure reliable fermentations and improve cheese production efficiency. © 2026 The Author(s). International Journal of Dairy Technology published by John Wiley & Sons Ltd on behalf of Society of Dairy Technology.