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Lisa Van de Water “The Bad Wine Lady”. Vinotec Napa 607 Cabot Way, Napa, CA 94559 Technical 707-953-7072 Fax 707-224-4028 Direct email: Diagnosis and treatment of sluggish/stuck fermentations. IF FERMENTATION STOPS OR SLOWS DOWN, ACT RIGHT AWAY.

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Lisa Van de Water“The Bad Wine Lady”

Vinotec Napa

607 Cabot Way, Napa, CA 94559

Technical 707-953-7072

Fax 707-224-4028

Direct email:

if fermentation stops or slows down 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.
stuck sluggish fermentations history
Stuck/sluggish fermentations: History
  • The first thing is to gather all data and observations on the fermentation, from the vineyard onward.
  • For a guide to compiling a history and current status, download “Stuck and Sluggish Questionnaire” at:

causes of stuck sluggish ferments from dr linda bisson
Causes of Stuck/Sluggish Ferments(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 analysis
Stuck/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 sensory
Sluggish 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 wines
Danger 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 microscopic exam for yeast
Stuck/Sluggish Ferment: Phase-contrast microscopic 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 microscopic exam for bacteria
Stuck/Sluggish Ferment: Phase-contrast microscopic 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 wines
Lactic spoilage in stuck wines

“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
    • 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
Handling Lactobacilli in fermenting or 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 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
Reinoculating a sluggish/stuck ferment
  • 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: