Spontaneous MLF in high acidity wines produced in cool-climate regions remains problematic though indispensable for the development of sensory characteristics. Genetic aspects and phenotypic traits of thirty-six Oenococcus oeni strains, most of them isolated from Valtellina wines over three consecutive years, were investigated. Molecular typing achieved by RAPD PCR and PFGE analyses allowed 27 different genotypes to be discriminated, whereas from the comparison of results arising by physiological tests (sugar fermentation, alcohol resistance, growth at low temperatures, biogenic ammines production) 28 different phenotypic profiles were obtained. Particularly, 69% of Valtellina isolates were able to develop at 5 degrees C in cultural broth. Micro-vinification experiments allowed the selection of strains with potential oenological performances and an interesting capability to grow in cold conditions was confirmed. Some O. oeni strains formed phenylethylamine (up to 47 mg/L) and tyramine (up to 36 mg/L) both in cultural broth and wine.