Non-starter lactic acid bacteria enter cheese as contaminants and influence cheese flavor development in a positive, neutral or negative manner. However, the diversity of these microbial contaminants, the substrates from which they derived energy, and the metabolic pathways they use to grow and influence cheese flavor development remain poorly characterised. This manuscript describes research that examines the genetic diversity of Lactobacillus casei isolates from different ecological niches, as well as the substrates and metabolic pathways that support the growth of non-starter lactic acid bacteria in ripening cheddar cheese.