RESTART AND/OR COMPLETE A STUCK FERMENTATION
Stuck and sluggish fermentations can cause significant economic losses for a winery due to extended labour requirements and purchase of additional yeast and nutrients to restart the fermentation. The wine quality is often significantly impacted causing additional financial loss. Extended periods of time with residual sugar and lack of SO2 protection increase the risk of microbial spoilage primarily due to Acetobacter spp and Brettanomyces bruxellensis. Many of the factors contributing to stuck fermentations are found in the must before the yeast is inoculated. But often stuck and sluggish fermentations are an adaptive process with a number of factors culminating to arrest the fermentation.
What causes stuck fermentations?
- Insufficient levels of YAN relative to the potential alcohol (plant deficiency, excessive water
additions, high potential alcohol). - A compromised yeast population (temperature shock, stress, lipid deficiency).
- Incorrect yeast selection (yeast strain unsuitable for wine chemical parameters).
- Inhibitory factors (Agrochemical residues, metal ions, short chain fatty acids, volatile acidity >0.8 g/L acetic acid)
How can I avoid a stuck fermentation?
- Measure Yeast assimilable nitrogen YAN in the grapes to understand if there is a known deficiency.
- Use a nitrogen calculator to calculate how much and which kind of nitrogen to add
- Use a rehydration nutrient with a high ergesterol content to ensure yeast can remain viable
to the end of fermentation (For high alcohol red wines particularly). - Select a suitable yeast for the wine choice (For example appropriate alcohol tolerance).
- Juice chemistry analysis to ensure there are no inhibitory factors (Yeast will not grow under pH 2.8 and above 0.8 g/L acetic acid, so ensuring that the must chemistry permits the multiplication of yeast cells before the fermentation has even begun is critical).
- Baume/Glucose and fructose separately/VA/pH/TA
- Assess grape sanitary state (Laccase testing, glucan testing).
1. PRELIMINARY OPERATION ON STUCK WINE (VISIT LAFFORT DECISION MAKING TOOLS FOR A TAILORED PROTOCOL)
- Rack/centrifuge avoiding air.
- Adjust wine temperature to 20°C (68°F).
- Adjust SO2 at 1-2 g/hL (10-20 ppm).
- Add:
- For white wines: BI-ACTIV®: 40 g/hL (400 ppm).
- For red wines: OENOCELL®: 40 g/hL (400 ppm).
- Mix wine anaerobically every 12 hours for 24 hours.
- Move on to step 2.
2. PREPARATION OF THE YEAST INOCULUM
2.1 Preparation of the wine for the yeast inoculum
- Take 5 hL of the volume of the treated stuck wine from step 1.
- Adjust the alcohol to 8 %, the sugar content to 20 g/L and the temperature
to 20°C (68°F). - Add THIAZOTE® PH: 20 g/hL (200 ppm) to this volume of wine and mix
thoroughly
2.2. Yeast preaparation
- Prepare 60 L of water at 40°C.
- Add the yeast rehydration nutrient SUPERSTART® SPARK or
SUPERSTART® ROUGE: 30 g/hL (300 ppm) of the volume of wine to be
treated, then homogenise. - Add ACTIFLORE® B0213: 30 g/hL (300 ppm ) of the volume of wine to be
treated, then homogenise. - Wait 20 minutes, then homogenise
- Add immediately 20 L of treated wine from step 2-1.
- Wait 10 minutes, let cool to 20°C and maintain the temperature
between 20-25°C . - The total time of the yeast rehydration must not exceed 45 minutes
2.3. Acclimatation of the yeast preparation
- Add the yeast preparation (Step 2.2) to the prepared wine for the yeast
inoculum (step 2.1). - Measure the Brix and maintain the inoculum at 20°C with
aeration until 0.5°Brix (avoid the total exhaustion of sugars in the
inoculum and a fall in the yeast activity). Aerate as soon as AF starts. - Double the volume with treated wine (step 1) at 20°C.
- Measure the Brix and maintain again the inoculum at 20°C until
0.5°Brix. Aerate again when fermentation becomes active.
3 INCOROPORATION OF YEAST INOCULUM IN THE TANK
- Add the yeast innoculum to the treated wine (step 1), maintain at 20°C.
• Add 30 g/hL (300 ppm) of NUTRISTART® ORG to the total volume of
the tank to the treated wine (Step 1).
