Microbiological stabilisation of grape musts and wines by high hydrostatic pressures

High hydrostatic pressure (up to 1000 MPa) is a new microbiological stabilisation process that can contribute to wine and grape must stabilisation. Experiments on grape must and wine microbiological stabilisation using high pressures were undertaken. A high pressure pilot plant mod. QFP6 of the ABB (Asea-Brown-Boveri) Society (Sweden) working up to 900 MPa was used. Flexible polyethylene bags (20-50 ml sample volume) were immersed in water contained in a 1-l treatment steel cylinder. Different pressures (300-900 MPa) were tested, combined with different oenological conditions (pH, content of alcohol, SO 2 , sugars and acetaldehyde) both with must and wine added with 106 cells per millilitre of each of 13 wine yeast species, 1 Leuconostbc oenos, 1 Lactobacillus sp., 1 Acetobacter and 1 Botrytis cinerea as vegetative and sporified cultures. Micro-organism inhibition and organoleptic consequences were determined. The results show that all the micro-organisms added to a Moscato wine (8.22% alcohol, 50.5g l -1 residual sugars, 146mg l -1 acetaldehyde, pH3.0 and 3.5, 64 mg l-1 SO 2 ) were killed in 2 min with pressurisation at 400 MPa and an initial temperature of 20°C. In contrast, in a Barbera grape must (pH 3.0, sugars 177.2 gl -1 , without SO 2 , ethyl alcohol totally absent) at 600 MPa there were some survivors of Schizosaccharomyces pombe. Samples of Asti Spumante sparkling wine were treated at 600 MPa for 2 min in comparison with an equal series of untreated samples. After 6 and 24 h and 10, 20, 40 and 90 days, pressurised and control samples were analysed for dissolved oxygen content, colour intensify and tonality, and tasted for organoleptic quality. Notwithstanding a stronger decrease of dissolved oxygen found after 6 h in pressurised samples after 5 min from air injection, no significant taste and olfactor differences were observed between control and pressurised samples after 90 days of anaerobic storage.