Keys for a Successful Malolactic Fermentation
October 2014
Volume 5 Keys for a Successful Malolactic Fermentation
What is malolactic fermentation (MLF)? MLF is a biological de-acidification of wine by bacteria that transforms malic acid into lactic acid with CO 2 production. In addition to de-acidification, MLF impacts include sensory changes and biological stability toward further degradation of L-malic acid.
What happens when MLF is not controlled? Oenoccocus oeni is the desired bacteria species to conduct MLF in wine, but not the only one… Lactobacillus and Pediococcus strains are often found in juice and wine and can be dominant. Uncontrolled MLF is an open door for every other organism present. It often generates negative aromas, such as rancid yogurt, sweat, burnt matches and rotten fruit, and a loss of balance and complexity.
Table 1: Undesirable changes due to uncontrolled MLF What? Who? Production Results in Wine Fermentation of volatile acidity, negative Lactic acid bacteria lactic acid, acetic acid residual sugar aromas, loss of complexity volatile acidity, loss of Tartaric acid Pediococcus lactic acid, acetic acid, CO balance, formation of decomposition Lactobacillus 2 unpleasant aromas Glycerol Lactobacillus acrolein volatile acidity, bitterness decomposition Pediococcus 4-vinylphenol, 4-vinylguaiacol, horse sweat, leather, smoke Volatile phenols Lactobacillus 4-ethylphenol, 4-ethylguaiacol and medicine notes Brettanomyces Ropiness (oily Pediococcus glucose-derived Increase viscosity wine) meaty, vinegar, dirty Biogenic amines Lactic acid bacteria biogenic amines aromas, human health concerns Lactobacillus N-heterocycles, unpleasant aftertaste, Mousiness Oenoccocus 2acetyl-1-pyrroline, nauseating characters, Brettanomyces 2acetyltetrahydropyridine (urine-soaked mouse cage)
An inoculation with selected bacteria reduces the potential of spoilage by other micro-organism thus ensuring rapid onset of MLF and better control over the production of aromatic compounds and wine mouthfeel.
Principal factors influencing most strains of lactic acid bacteria: • Wine pH influences bacteria growth, viability and activity.
• Sulfur dioxide (SO 2) strongly reduces the growth of bacteria and inhibits their activity. For most
strains Total SO 2 = 30mg/L tolerance o Bacteria growth and activity is inhibited by alcohol; bacteria can be stressed above 6%. For most strains alcohol tolerance = 14%. • Optimal growth and activity temperature is between 60-85°F (15-30°C). Other parameters can impact MLF such as: vineyard sprays, micro-organisms (competition for nutrients, production of SO 2 and/or production of toxic compounds for bacteria), ease of alcoholic fermentation or even tannin content of the wine.
When to do MLF? Lactic acid bacteria can be added to the wine at different times: • 24-48 hours after yeast inoculation = “co-inoculation” • During alcoholic fermentation = “sequential inoculation” • After alcoholic fermentation = “classic method” Co and sequential inoculations are usually practiced to limit the risk of contamination by other micro- organism, to produce fresh, fruity and less buttery wines and save time and energy. The main risks to consider are stuck alcoholic and/or ML fermentations, sugar consumption by lactic acid bacteria and an increase of volatile acidity. To limit the risks of co/sequential inoculations, it’s important to: - Have a problem-free alcoholic fermentation: lower alcohol levels, healthy grapes, good yeast nutrition, lower pH - Use yeast compatible with MLF
- Moderate Total SO 2 additions in pre-fermentation <50mg/L - Control fermentation temperature: 60-77°F (16-25°C)
Which bacteria for which wine? To increase the rate of MLF completion, it is important to choose bacteria adapted to the wine criteria.
Enartis Strain ML MCW ML Silver ML One Species Oenococcus oeni Liquid Available forms Freeze-dried Direct Direct Direct pH tolerance 3.1 3.1 3.3
SO 2 resistance (mg/L) 30 45 40 Alcohol tolerance 16 15 14 (%v/v) Temperature (°F) 55-75 55-75 55-75 Activity speed High High Moderate
Nutrition for lactic acid bacteria: As any organism, the bacteria need to eat to survive, develop and be active! Bacteria need acclimation before introducing them into the hostile environment of wine. NUTRIFERM OSMOBACTI is a nutrient and regulator of osmotic pressure that helps bacteria survive in wine, activate their metabolism and increase their activity. NUTRIFERM OSMOBACTI should be used in rehydration water, before inoculation. Lactic acid bacteria need amino acids, co-factors and vitamins in their metabolism. NUTRIFERM ML provides nutrients specific for bacteria and polysaccharides and cellulose to adsorb compounds that may inhibit cell growth. It helps the bacteria to colonize the wine over natural flora and to complete MLF.
How to prepare freeze-dried malolactic bacteria in 4 steps: Step 1: Dilute in 20 x volume of chlorine-free warm water (68-75°F). Wait 15-20 min. Step 2: Add NUTRIFERM OSMOBACTI (2g/hL of wine to inoculate) and mix gently. Wait 3-4 hours. Step 3: Pump bacteria starter into wine and mix gently via pump-over. Step 4: Add NUTRIFERM ML (20-30g/hL) to wine during the pump-over.
Want to know which bacteria will complete MLF in your wine? Try the Quick ML Activity Test! To maximize the rate of successful MLF, Enartis Vinquiry has developed a method that helps the winemaker to understand how challenging MLF will be and identify the best bacteria strain to use in a specific wine. This method, based on malic acid consumption in controlled conditions, will rate the wine/bacteria strain pairing.
If you have any questions, please give us a call at (707) 838-6312.