RESTARTING STUCK MALOLACTIC FERMENTATION
Recommendations from Lallemand North America
Winemakers are aware that Oenococcus oeni bacteria, traditionally responsible for malolactic fermentation (MLF), are
successful only when the bacteria can adapt to the harsh environment of a fermenting must or a finished wine. The usual
factors influencing the success of MLF include pH, temperature, alcohol and SO2 (both free and total). Problems can arise
when pH levels are low (under 3.4), alcohols are high (greater than 14%), the temperature of the wine is low (less than
18°C [65°F]), or the molecular SO2 is high (greater than 0.3 mg/L). Other inhibitory factors, such as nutrient availability,
high volatile acidity (greater than 0.4 g/L), high levels of condensed tannins and/or agrochemical residues, may also cause
stuck MLF. Under cool climate conditions, where the initial L-malic content is in excess of 5 g/L, LAB can be inhibited by
L-lactic acid contents in excess of 1.5 g/L. Under these conditions, MLF will initiate, but the resulting high L-lactic acid
content can inhibit the malolactic bacteria (MLB), thus preventing MLF from proceeding to completion. Limiting conditions
have a combined cumulative effect, making life truly difficult for the MLB. If several stressful conditions coincide, often MLF
will not go to completion, resulting in a stuck MLF.
To restart and complete a stuck MLF, sometimes it is enough to simply add and gently mix in 20 g/hL (1.7 lb/1000 US gal) of
a nutrient such as ML Red Boost™ for red wines or Opti’ML Blanc™ for white wines. If that fails to restart the MLF, a more extensive protocol using a 1-Step® starter kit is necessary. The Lallemand MLF R&D team, headed by Dr. Sibylle Krieger-Weber,
has developed a wine MLB acclimatization strategy for use with the 1-Step® starter kit, which allows wines undergoing a
stuck MLF to proceed to completion. Lallemand offers four different sizes of 1-Step® starter kits, each containing a sachet
of a selected MLB and another sachet containing an activator. The activation and adaptation of the MLB can be critical in
reducing the effect of an unfavorable wine matrix on the bacteria, thus favoring successful completion of MLF.
If an MLF is encountered that will not proceed to completion, Lallemand has devised a fermentability test to determine
whether a wine is capable of completing MLF when re-inoculated with the 1-Step® starter kit. The test can be performed
by utilizing the following procedure.
1. Immediately before undertaking this test, accurately determine the L-malic acid content (mg/L) of the stuck wine and
record this value as MA 1.
2. Rehydrate the contents of a 2.5 hL sachet of VP41 MBR® or ALPHA MBR® in 50 mL of clean chlorine-free water at 20°C
[68°F]. Gently stir and let rehydrate for 10 minutes.
3. Inoculate 1000 mL of the stuck wine with 2 mL of the bacterial suspension from step 2. This gives a 10x higher inoculation
rate.
4. Maintain the temperature of this 1000 mL of stuck wine at 20°C (68°F) for 72 hours.
5. After the 72 hours, accurately determine the L-malic acid (g/L) content of this 1000 mL stuck wine and record this value
as MA 2.
6. Using the L-malic acid content values measured before inoculation and again after 72 hours, calculate the percentage of
malic acid decrease by using the following formula: (MA 2 / MA 1) x 100 = % of malic acid decrease.
Contact your local Lallemand representative for advice if the result is less than 20% malic acid degradation within 72 hours,
as there is a high level of MLF inhibition in the wine.
However, if the result of the fermentability test shows a greater than 20% malic acid decrease within 72 hours, the 1-Step®
restart protocol may be used to restart the stuck MLF. The procedure is described on the next page.
RESTARTING STUCK MALOLACTIC FERMENTATION
Adaptation protocol for handling stuck malolactic fermentations
Stage 1. Pre-treat wine and adjust temperature
Prepare the wine undergoing stuck MLF to receive the activator and selected MLB contained in the 1-Step® starter kit.
The wine should be separated from any lees either by racking or by normal lees removal filtration. This step will help to
remove any potential inhibitory factors or unwanted spoilage organisms. In addition, cross-flow or 0.45 micron membrane
filtration may be necessary to control undesirable bacteria such as Lactobacillus or Pediococcus.
In some cases of stuck MLF, the wine may be suspected of containing substances which may be toxic to malolactic bacteria.
If that is the case, Lallemand recommends pre-treatment of the wine with Nutrient Vit End™ at 30 g/hL (2.4 lb/1000 US
gallons). The Nutrient Vit End™ suspension is prepared in either water or wine then added to the stuck wine with sufficient
mixing. Rack the wine off the Nutrient Vit End™ lees after 48 hours.
Finally, adjust the temperature of the stuck-MLF wine to 18° to 22°C (65° to 72°F).
Stage 2. Prepare the 1-Step® starter kit
Refer to the LIQUID VOLUME TABLE below to determine the size of 1-Step® starter to be used, keeping in mind the 1-Step®
starter kit for restarting a stuck MLF requires twice the normal dosage to compensate for the more difficult MLF environment encountered in a stuck MLF.
Rehydration Phase
1. Mix and dissolve contents of the activator sachet in drinking water.
2. Adjust temperature between 18° and 22°C (64° and 72°F)
3. Add contents of the bacteria sachet and dissolve carefully with gentle stirring.
4. Wait 20 minutes.
Acclimatization Phase
1. Mix the 1-Step® preparation (activator and bacteria dissolved in drinking water) with wine, ensuring a pH greater than 3.5.
2. Verify that the temperature is between 18° and 22°C (64° and 72°F).
NOTE: If the stuck wine has less than 1.0 g/L of L-malic acid, wait 6 to 8 hours before inoculation. If the stuck wine has
greater than 1.0 g/L of L-malic acid, wait 12 to 18 hours before inoculation.
Inoculation
1. Inoculate the wine with the acclimated culture.
2. Maintain the temperature between 18° and 22°C (64° and 72°F)
3. Check for MLF activity by analyzing for L-malic acid degradation every 2 to 4 days.
LIQUID VOLUME TABLE
Rehydration Phase
Acclimatization
Phase
Inoculation
ALPHA™ for 25 hL
Dissolve ALPHA™
Mix ALPHA™ (2.5 L)
Inoculate 12.5 hL (330 gals) of wine
(660 gals)
in 2.5 L of water
with 2.5 L of wine
with ALPHA™ culture (5 L)
VP41™ for 100 hL
DissolveVP41™
Mix VP41™ (10 L)
Inoculate 50 hL (1,320 gals) of wine
(2,640 gals)
in 10 L of water
with 10 L of wine
with VP41™ culture (20 L)
VP41™ for 500 hL
Dissolve VP41™
Mix VP41™ (50 L)
Inoculate 250 hL (6,600 gals) of wine
(13,200 gals)
in 50 L of water
with 50 L of wine
with VP41™ culture (100 L)
VP41™ for 1000 hL
Dissolve VP41™
Mix VP41™ (100 L)
Inoculate 500 hL (13,200 gals) of wine
(26,400 gals)
in 100 L of water
with 100 L of wine
with VP41™ culture (200 L)