You think you have a stuck ferment…what next ?

Ferments have many reasons for being sluggish or stuck

• Inappropriate yeast selection

• Killer factor in yeast selection

• Mis-handling of yeast during inoculation

• Low YANs in fruit

• Not enough nutrients to support fermentation

• Competing unwanted yeast or bacteria

• Alcohol toxicity in high sugar concentrations

• Excessive temperatures

• Anaerobic fermentation

• Metabolic by-products 

• Unbalanced or inhibitory acid, pH and SO2

Analysis required for confirmation and treatment

• Yeast Viability/count

• Micro exam – looking for lactobacillus and acetobacter

• VA or Acetic acid analysis

• Alcohol analysis

• Glucose and Fructose analysis separated

• Sensory

• Monitor density decrease once below 1.005

• Measure YAN

• Check Free SO2 and TSO2 even if the vineyard/winery hasn’t added any

Encouraging Ferment

• If yeast viability is >25%, alcohol is <12%, VA <0.8g/L encouraging a ferment is recommended rather than a restart

• Aeration – pump over

• Heat or Cool to 18-22°C

• Nutrient addition – increase YAN to 20mg/L

• Yeast hull addition, max 30g/hL

• Rack off lees

• Additional lees (active clean lees) where appropriate

• If still not moving look to restarting

Re-starting ferment

• If yeast viability is <25%

• Rack off lees

• Warm to 20-25°C

• Build grape based reinoculation solution

• Select and rehydrate Fructophilic yeast, suitable for the environment ( high alcohol, or SO2)

• Follow re-start protocol for yeast/nutrient

• Yeast hull addition, max 30g/hL

• Aerate

• Rack off lees

• Monitor analysis of residual sugar, alcohol and VA

High VA > 0.8 g/L

• VA removal should be considered

• VA greater than 1g/L will inhibit yeast

• Or filter to reduce bacterial load

• Reverse osmosis or similar if above 

• Treat with an antimicrobial /spoilage product like X-PRO Bactoclean