impact of malolactic fermentation strain on wine composition
DESCRIPTION
Impact of Malolactic Fermentation Strain on Wine Composition. Lucy Joseph U.C. Davis Department of Viticulture and Enology. Outline. Introduction to malolactic fermentation (MLF) Lactic acid bacteria metabolism Commercial inoculum Wine matrix effects Interaction with oak - PowerPoint PPT PresentationTRANSCRIPT
Impact of Malolactic Fermentation Strain on
Wine Composition
Lucy JosephU.C. Davis Department of Viticulture
and Enology
Outline
• Introduction to malolactic fermentation (MLF)• Lactic acid bacteria metabolism• Commercial inoculum• Wine matrix effects
– Interaction with oak• Timing of inoculation
Malolactic Fermentation
• Any wine containing malic acid could be considered unstable.
• Certain indigenous bacteria can metabolize malic acid as a very poor carbon and energy source in the fermenter and in the bottle.
• Conversion of malic to lactic acid by a controlled malolactic fermentation prior to bottling eliminates the instability.
• It can be a problem to start, very slow activity, long time to finish and can start and stop.
MALOLACTIC BACTERIA
• What are they?– “bacteria”: single-celled non-nucleated
microorganisms– “lactic acid bacteria”: produce lactic acid from
sugar• Acid loving• Nutritional fastidious• Carry out many food fermentations
Malolactic bacteria are lactic acid bacteria which can convert malic acid
to lactic acid:
stronger acid weaker acid
2 carboxyl groups 1 carboxyl group
Malic Acid
CO2
Lactic Acid + Carbon Dioxide
Oenococcus oeni
• Only two species• Oenoccocus oeni (formerly
Leuconostoc oenos) are only found in wine
• Oenococcus kitaharae was ‘discovered’ in 2006 in the spoiled remains of a sake mash (shochu, high pH) and lacks the gene for malolactic fermentation
What happens during a malolactic fermentation
• Deacidification– Each gram per liter of malic converted to lactic
creates a loss of 7.46 mM/L of titratable H+ ions, or 1.12 grams/L as tartaric measured by titration (TA)
• pH changes• Micronutrients are sequestered• Secondary metabolites can contribute to the
flavor profile
THE COURSE OF THE MLFBacterial growth is finished several days after the conversion of malate to lactate. Full bacteria growth in wine is only 107 cells/mL, and the malate has usually disappeared at 106 cells/mL. (Diacetyl may be being formed at that time.)
Bacteria Positives NegativesOenococcus
oeni Reduction of total acidityIncrease in volatile acidity
(high pH and residual sugar)
Increase microbial stabilityProduction of biogenic amines
and ethyl carbamate
Reduction of ketone and aldehyde
equivalents (reduces SO2 use)Spoilage aromas (mousy,
sweat, sulfur)
Reduction of grassy, vegetative notesLoss of varietal aromas and
fruity esters
Enhanced mouthfeel
Increase of diacetyl and other aroma
and flavor compoundsExcess diacetyl production
Out-competes other bacteria
Enhanced color stability
(co-pigmentation) Loss of color (high pH)Lactobacillus
plantarum Reduction in total aciditySensitive to low pH and high
alcohol
No acetic acid production Sluggish fermentation
Production of spoilage aromas
Relevant Metabolic Activity in Oenococcus oeni
ML Metabolism
Buttery Characte
r Diacetyl
Acetaldehyde Conversion
J.P. Osborne et al. /FEMS Microbiology Letters 191 (2000)
Mousy Character
Commercial Malolactic Strains
Oenococcus oeniLactobacillus plantarum
Commercial Strains - Inoculation
• Direct inoculationBacteria is pre-adapted and can be added
directly to the fermentation• One step strains
Bacteria need to be rehydrated and grown for 24 hours prior to addition
• TraditionalRequires growth and build up of inoculum
prior to addition
Commercial Strains-Selection Criteria
pH tolerance Alcohol tolerance SO2 tolerance Temperature range Competitive ability
Stuck MLF
Biogenic amine production
Commercial Strains-Sensory
• Diacetyl production• Color stability• Mouthfeel• Varietal enhancement• Avoidance of defects, i.e. vegetative, sulfur• Interaction with oak
Wine Matrix Effects
Cultivar & Strain Influence
Compounds found in MLF wines by GC-MS
Purge and trap system of Montrachet wines•4-Methyl-3-pentenoic acid•Methyl acetate (Sweet, solvent-like)•Ethyl hexanoate (Fruity, rum-like)•Hexyl acetate (Fruity)
Freon 114 extraction of Epernay 2 wines•1,12-Tridecadiene*•Hexadecanoic acid (mild waxy)*•1,2-Benzene dicarboxylic acid (mild ester)*•Farnesol (floral)*
*Spectral fit < 900Am. J. Enol. Vitic., Vol. 43, No. 3, 1992R. M. AVEDOVECH, M. R. McDANIEL, B. T. WATSON, and W. E. SANDINE
Other Reported Flavor Enhancers
• 1-hexanol - fruity• ethyl acetate - fruity• ethyl lactate - buttery • diethyl succinate - brandy• butyrolactone – aroma enhancer• glycoaldehyde – aroma complexity,
browning
MLF in Oak
Bacteria can breakdown glycosides in solution to release the aglycone
Breakdown of Glycosides
Glycosidic activities for a selection of Oenococcus oeni strains on four substrates: p-nitrophenyl-β-D-glucoside, p-nitrophenyl-α-L-arabinofuranoside, p-nitrophenyl-α-L-rhamnopyranoside, p-nitrophenyl-β-D-xyloside
Tannat Wines- Different MLF-Before Aging
Control (gray filled square), MLF with DSM 7008 (black filled square)and D-11 (open square)
J. Agric. Food Chem. 2009, 57, 6271–6278. E. Boido, K Medina, L. Farina, F. Carrau, G. Versini, E. Dellacassa
Timing of InoculationInoculation Advantage Disadvantage
Pre-fermentation MLF completion Reduced nutrients for AF
Production of yeast inhibitors such
as acetic acidEarly-
Fermentation Simple-shorter production time Increased acetic acid production
Tends to avoid MLF failureIncompatibility of yeast and
bacteria
Allows optimization of management
throughout the fermentation Mid-
FermentationBetter domination of the MLF by inoculated
strain Incompatibility issues
More traditional, allowing AF to complete
before MLF completion Post-
fermentationMLF occurs after AF is complete allowing
better control of temperature and SO2 levels Some compatibility issues MLF can be done in barrels Nutrients are depleted Less color loss Inhibitors may be high i.e. alcohol
Summary
• Reduction in acid• Production of desirable compounds (diacetyl)• Production of other flavor compounds during
growth (1-hexanol, ethyl acetate, ethyl lactate, diethyl succinate, butyrolactone, glycoaldehyde, glyoxal, 2,3-butanediol, caprylic acid, hydroxycinnamic acid)
• Release of aglycones from glycosides in the wine