An immobilized cell bioreactor for the malolactic fermentation of wine : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Technology in Biotechnology at Massey University
Malolactic fermentation using immobilized cells of Leuconostoc oenos was investigated in order to improve this fermentation at an industrial-scale.
Three strains of bacteria were investigated in some detail, and one was chosen for further work. A satisfactory growth medium for the strain of bacteria used was found to be an apple juice broth. The effect, on both the growth and malic acid bioconversion for Leuconostoc oenos strain 1070, of having 6% v/v ethanol in the growth media was tested and found to cause a longer lag phase, and be slightly beneficial, respectively.
Oak chips were decided on as the immobilization media, in preference to bone char, and a synthetic, apple-juice based wine was used to determine operation parameters for a continuous culture bioreactor.
Temperature, pH, ethanol concentration, SO2, malic acid concentrations, anaerobic conditions and dilution rate were investigated and it was shown that lower malic acid concentrations, and also an interaction between low pH, high temperature and high ethanol concentration affected the malic acid bioconversion adversely. Increasing the dilution rate above 0.35 h·1 caused a 30% drop in the bioconversion rate. The pH level had no effect on bioconversion if the temperature was kept at 21°C or lower. Decreasing the temperature, increasing the ethanol concentration above 10% v/v and increasing SO2 levels all caused a slight drop in bioconversion rates while strict anaerobic growth and bioconversion conditions caused an increase. The bioconversion rates ranged between 20 and 100 mg malic acid consumed/lO0ml oak chips/hour.
An industrial prototype bioreactor was built and used at Villa Maria Wineries, Auckland, during the 1991 vintage and successfully processed 200 litres of Chardonnay-style wine in 2 days. The bioconversion rate was between 25 and 30 mg malic acid consumed/l00ml oak chips/hour. Informal taste tests showed satisfactory malolactic characteristics in the treated wine.