Malo‐lactic fermentation in australian dry red wines

Abstract

Malo‐lactic fermentation occurred in 62% of 466 Australian dry red wines of 1968 vintage at 6 months of age. In a further 9 % of wines the fermentation was still in progress. Wines which had undergone the fermentation were less acid than those which had not. The difference was greater in wines made from Cabernet Sauvignon than from Shiraz or Grenache grapes. The winery in which the wine was made strongly influenced the occurrence of malo‐lactic fermentation in a particular wine‐growing area, and was the most important factor involved. Incidence of malo‐lactic fermentation was closely correlated with the presence of Leuconostoc and Coccus in the wine, but less so with Lactobacillus. Leuconostoc, Lactobacillus and sometimes Coccus occurred together, but no wines contained both Lactobacillus and Coccus. Diacetyl content of the wines ranged from 0 to 7.5 ppm. In wines which had undergone malo‐lactic fermentation the mean diacetyl content was 2.8 ppm, compared with 1.3 ppm for wines which had not undergone this. Diacetyl content of wines made from Grenache was not significantly different, with respect to the occurrence or absence of malo‐lactic fermentation. The statistical significances of the various inter‐relationships between malo‐lactic fermentation, type of bacteria present and certain wine constituents are assessed. Estimates of variance components of II constituents of Australian dry red wines are given, and these may be used in designing future sampling surveys.

Effect of pH, Temperature and S02 Concentration on the Malo-Lactic Fermentation Abilities of Selected Bacteria and on Wine Colour

“…Malo-lactic fermentation (MLF) entails the bacterial conversion of malic acid (a dicarboxylic acid) to lactic acid (a monocarboxylic acid) and C02, thus partially deacidifying the wine (Suverkrop & Tchelistcheff, 1949;Ingraham, Vaughn & Cooke, 1960;Ribereau-Gayon & Peynaud, 1964;Rankine, 1970), and occurs naturally in the dry wines of many countries (Kunkee, Ough & Amerine, 1964). In countries with colder climates where the wines sometimes have very high acidities, MLF is an important means of deacidification.…”

“…In South Africa MLF poses a problem in wines which already have pH-values (Van Wyk, 1976) unless the pH can be satisfactorily decreased by the addition of acid. Malo-lactic fermenta· tion is the most effective means of ensuring that a wine is biologically stable (Ribereau-Gayon & Peynaud, 1964;Maret & Sozzi, 1977;Rankine, 1977); however, it should not occur after bottling as it may produce an undesirable haze and gas in the wine (Ribereau-Gayon & Peynaud, 1964;Rankine & Bridson, 1971). The only practical way to ensure a swift MLF is inoculation with a suitable strain of malo-lactic bacteria (Vaughn & Tchelistcheff, 1957;Castino, Usseglio-Tomasset & Gandini, 1975;Lafon· Lafourcade, 1975;Beelman, Gavin & Keen, 1977).…”

“…Malo-lactic fermentation takes place most readily in *This work forms part of a thesis of the senior author accepted for the M.Sc.-degree at the University of Stellenbosch. low-acid wines (Ribereau-Gayon & Peynaud, 1964;Bousbouras & Kunkee, 1971;Van Wyk, 1976;Rankine, 1977). Leuconostoc species are able to decompose malic acid at lower pH-levels than most other bacteria (Rankine, 1970;Castino et al, 1975), and one species may even effect MLF at pH 3,0 where all growth of this species is inhibited (Lafon-Lafourcade, 1975).…”

“…Low pH has a synergistic effect on the inhibitory activity of S02 (Kunkee, 1967 a;Castino et al, 1975). Sugars, aldehydes and anthocyanin pigments readily bind S0 2 (Vaughn, 1955;Kunkee, 1967b;Rankine, 1977) so that the concentration of free S02 in dry red wines is usually less than 4 mg/C (Rankine, 1977).…”

“…The bound form of S02 is less active than the free form against malo-lactic bacteria (Vaughn, 1955;Kunkee, 1967b;Rankine, 1977), but it may also inhibit MLF (Kunkee, 1967b;Lafon-Lafourcade, 1975). The inhibitory effect of bound S02 may be due to bacterial attack on the aldehydes, which would set S02 free (Fornachon, 1963).…”