Transcript Stuck Fermentations 2000

Lisa Van de Water
“The Bad Wine Lady”
Vinotec Napa
607 Cabot Way, Napa, CA 94559
Technical 707-953-7072
Fax 707-224-4028
www.vinotecnapa.com
Direct email: [email protected]
Diagnosis and treatment of sluggish/stuck
fermentations
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IF FERMENTATION STOPS OR SLOWS
DOWN, ACT RIGHT AWAY
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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.
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Stuck/sluggish fermentations: History
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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
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Causes of Stuck/Sluggish Ferments
(from Dr. Linda Bisson)
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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: Analysis
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Test MLF, pH, VA to see if lactic acid bacteria have grown.
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Test glucose and fructose separately, not together
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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
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It is difficult to prepare the sample to exclude bubbles but without
losing alcohol through aeration.
Sluggish Ferment: Sensory
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Taste carefully for:
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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 Wines
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Activity (CO2)
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VA rise
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Lactobacillus and Acetobacter raise VA
Unpleasant aroma/flavor
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Check under microscope, may be Lactobacillus
Sulfides, ethyl acetate, oxidation
Dekkera/Brettanomyces
Film on surface
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Acetobacter, surface film yeast
Stuck/Sluggish Ferment: Phase-contrast
microscopic exam for yeast
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Check an unstirred and a stirred/circulated sample for nonSaccharomyces yeasts, estimate percentage
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Test yeast viability with methylene blue stain
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Non-Sacch. yeasts can be seen even if they are dead
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
microscopic exam for bacteria
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Check for Lactobacilli (rod-shaped)
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Genetic tests for Lactobacilli
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PCR-based tests detect some but not all wine Lactobacilli
Pediococci (two small round balls stuck together)
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It is essential to stop their progress before they spoil the wine
by producing acetic acid from sugar (see: “5 choices”).
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 wines
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“Ferocious
Lactobacilli!”
- Dr Ralph Kunkee
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
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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
Handling Lactobacilli in fermenting or
stuck wine: 5 CHOICES
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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.
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Chill the must to < 60 F to stop Lactobacilli, decide what to do.
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Ignore it (THIS IS NOT A GOOD CHOICE!)
Lysozyme
Lysozyme disrupts the cell membrane of lactic acid
bacteria, killing them.
Add before yeast fermentation to prevent most cases of
Lactobacillus spoilage.
Add when Lactobacilli are seen under the microscope in
stuck wines.
Lysozyme does not affect yeast or acetic bacteria.
Reinoculating a sluggish/stuck ferment
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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
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Concentrate or sugar does not have the same effect
Add large amounts of nutrients but ONLY to the starter
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50 g/hL each of a complex nutrient and DAP to the starter
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Stir and aerate starter every day
Add stuck wine bit by bit to the starter, not vice versa!
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For details, download “Stuck Reinoculation” at:
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www.bsgwine.com/references.htm