Gram-negative psychrotrophic bacteria make up the dominant microflora of chilled raw milk. The dominant species identified, whatever the duration of refrigeration considered, are essentially: Aeromonas caviae (36%), Chryseomonas luteola (15%), Pseudomonas fluorescens (29%), Pseudomonas putida (11%) and Pseudomonas cepacia (3%). In addition to the presence of significant aminopeptidase and esterase activities in these psychrotrophic germs, they are also endowed with intense thermostable extracellular proteolytic and lipolytic activities, recognized as responsible for numerous taste and texture defects in dairy products. In addition, all these strains showed optimal extracellular proteolytic activity at casein concentrations of around 3-5%, pH levels of 6-8 and an optimal incubation temperature of 37°C. Key words : Raw milk, Refrigeration, Quality, Psychrotrophic strain, Identification