Lisa Van de WaterLisa Van de Water“The Bad Wine Lady”“The Bad Wine Lady”

Vinotec Napa607 Cabot Way, Napa, CA 94559

Technical 707-953-7072Fax 707-224-4028

www.vinotecnapa.comDirect email: badwinelady@aol.com

Diagnosis and treatment of Diagnosis and treatment of sluggish/stuck fermentationssluggish/stuck fermentations

2

IF FERMENTATION STOPS OR SLOWS IF FERMENTATION STOPS OR SLOWS DOWN, ACT RIGHT AWAYDOWN, ACT RIGHT AWAY

FIND THE CAUSE(S): To know what to do about stuck/sluggish ferment, you have to understand why the fermentation is in trouble (there is usually more than one cause).

The sooner that treatment is started, the more likely that the fermentation can be resumed.

Also, it is very important to deal with the problem before spoilage microbes attack the wine.

3

Stuck/sluggish fermentations: Stuck/sluggish fermentations: HistoryHistory

The first thing is to gather all data and observations on the fermentation, from the vineyard onward.

EVEN THE SMALLEST DETAIL MAY BE OF CRITICAL IMPORTANCE!

For a guide to compiling a history and current status, download “Stuck and Sluggish Questionnaire” at:

www.bsgwine.com/references.htm

4

Causes of Stuck/Sluggish FermentsCauses of Stuck/Sluggish Ferments(from Dr. Linda Bisson)(from Dr. Linda Bisson)

Nutrient limitation Nutrient imbalance Substrate inhibition Ethanol toxicity Presence of toxic substances Poor adaptation of strain Low pH Temperature shock

From Bisson & Butzke, “Diagnosis and Rectification of Stuck and Sluggish Fermentations, 2000

Stuck/Sluggish Ferment: AnalysisStuck/Sluggish Ferment: Analysis

Test MLF, pH, VA to see if lactic acid bacteria have grown.

Test glucose and fructose separately, not together If glucose is almost gone but fructose remains, yeasts will

probably not continue to ferment without reinoculation and addition of some new juice to add some glucose.

If glucose and fructose are approximately equal, an outside influence (cold, heat, SO2 addition etc) has affected the yeasts.

Test ACTUAL alcohol, not expected alcohol It is difficult to prepare the sample to exclude bubbles but

without losing alcohol through aeration.

Sluggish Ferment: SensorySluggish Ferment: Sensory

Taste carefully for: Sharp taste in finish (difficult when sugar is

present) Ethyl acetate Raisin/cooked character ACPY/ACTPY (mousy) Sulfides Any other undesirable sensory character

Watch for CO2, and film on surface

Danger Signals: Stuck WinesDanger Signals: Stuck Wines

Activity (CO2) Check under microscope, may be Lactobacillus

VA rise Lactobacillus and Acetobacter raise VA

Unpleasant aroma/flavor Sulfides, ethyl acetate, oxidation Dekkera/Brettanomyces

Film on surface Acetobacter, surface film yeast

Stuck/Sluggish Ferment: Phase-contrast Stuck/Sluggish Ferment: Phase-contrast microscopic exam for yeastmicroscopic exam for yeast

Check an unstirred and a stirred/circulated sample for non-Saccharomyces yeasts, estimate percentage Non-Sacch. yeasts can be seen even if they are dead

Test yeast viability with methylene blue stain If viability at least 25% and no Lactobacilli are present,

warm must to 18-22 C, add yeast hulls, stir every day If viability < 25%, settle and rack off dead yeasts before

proceeding

Watch for Brettanomyces, which grow readily in stuck ferments if they have become contaminated.

Stuck/Sluggish Ferment: Phase-contrast Stuck/Sluggish Ferment: Phase-contrast microscopic exam for bacteriamicroscopic exam for bacteria

Check for Lactobacilli (rod-shaped) It is essential to stop their progress before they spoil the

wine by producing acetic acid from sugar (see: “5 choices”).

Genetic tests for Lactobacilli PCR-based tests detect some but not all wine Lactobacilli

Pediococci (two small round balls stuck together) Sometimes present but only sometimes a problem at this

point; they cannot make acetic acid

Acetic bacteria can spoil stuck wines if air is available

Lactic spoilage in stuck winesLactic spoilage in stuck wines

Stuck wines are EXTREMELY susceptible! Lactobacilli often acclimate while yeast is being

encouraged Stimulated by nutrients/vitamins added to stuck ferments Even 50 ppm or > SO2 does not necessarily inhibit them

once they have acclimated to wine May grow very quickly, or slowly over months Activity is often mistaken for yeast fermentation Continue to produce acetic acid from sugars

Ethyl acetate is not made so there is NO SMELL Acetic acid > 0.9 g/L must be removed by R.O. before

reinoculation with yeast

“Ferocious Lactobacilli!”

- Dr Ralph Kunkee

Handling Lactobacilli in fermenting Handling Lactobacilli in fermenting or stuck wine: 5 CHOICESor stuck wine: 5 CHOICES

If MLF is finished you could decide that the wine is dry enough, add SO2 and start cleaning up the wine.

Add lysozyme, 300-500 ppm depending on population (check VA every 1-2 days for a while, to make sure that Lactobacillus activity stopped)

Tightly filter the wine until no bacteria are seen under microscope.

Chill the must to < 60 F to stop Lactobacilli, decide what to do.

Ignore it (THIS IS NOT A GOOD CHOICE!)

LysozymeLysozyme

Lysozyme disrupts the cell membrane of lactic Lysozyme disrupts the cell membrane of lactic acid bacteria, killing them.acid bacteria, killing them.

Add before yeast fermentation to prevent most Add before yeast fermentation to prevent most cases of Lactobacillus spoilage.cases of Lactobacillus spoilage.

Add when Lactobacilli are seen under the Add when Lactobacilli are seen under the microscope in stuck wines.microscope in stuck wines.

Lysozyme does not affect yeast or acetic Lysozyme does not affect yeast or acetic bacteria.bacteria.

Reinoculating a sluggish/stuck Reinoculating a sluggish/stuck fermentferment

Prepare a reinoculation starter (if no Lactobacilli) Use a vigorous yeast but not the same one you used before Use at least some grape juice, even 1% will help

Concentrate or sugar does not have the same effect Add large amounts of nutrients but ONLY to the starter

50 g/hL each of a complex nutrient and DAP to the starter Stir and aerate starter every day Add stuck wine bit by bit to the starter, not vice versa!

For details, download “Stuck Reinoculation” at:

www.bsgwine.com/references.htm