At Winemaking Tasmania we have developed an excellent protocol for bringing to completion struggling and stuck fermentations. This method has been used to successfully restart even the most difficult ferments such as a red wine which struggled through several restarts from around 20 g/l of residual sugar to finally become stuck fast at just under 7 g/l.

Following the processing described below this wine was re-inoculated and fermented to dryness in 4 days.

Process Background

It is generally accepted that an almost completed wine full of dead and dying yeast, relatively elevated levels of alcohol, perhaps slightly high levels of EA and VA and high levels of toxins from long chain fatty acids and other compounds is an unfriendly environment in which to introduce and successfully grow a re-start culture.

It is also clear that the off aromas and flavours generated in an attenuated struggling ferment are seriously detrimental to wine quality.

Three years of trials have proved to us that the following method works and is cost effective and most importantly has little or no impact on the final wine quality.

Standard Procedure:

1. At the first sign that fermentation is beginning to struggle and may not reach conclusion; then the following procedure should be followed.
2. Cool the wine to < 50C
3. Once below 50C add SO2 to achieve 20 ppm free
4. Allow the wine to settle for 4 to 6 days, (longer if possible) so that the bulk of the yeast and other solids are reasonably compact on the bottom of the tank. We have found that an addition of a small amount of bentonite (0.1 – 0.2g/l) may aid this settling.
5. Cross-flow filter the clear wine to a clean tank and warm to around 160C
6. Adjust the alcohol of the wine so that it is less than 14%. If appropriate the lower the better.
7. Pass the wine through a reverse osmosis plant and treat the permeate through an ion exchange column to reduce EA, VA and most importantly to remove long chain fatty acids and other toxins.
8. Prepare a re-start culture and re-inoculate following standard re-start procedures.

Steps 4 through 6 can be completed quite quickly, depending on the batch size and all the equipment and expertise is available from Winemaking Tasmania and is fully mobile and able to process most batch sizes down to 1,000 litres.

Conclusions:

We have developed, tried and tested this procedure over the vintages 2005 – 2007 and have found that it has worked in all cases. Wine quality has not been compromised and in fact has been significantly improved due to the fact that wines are no longer allowed to struggle through days and weeks of fermentation in an attempt to take them to completion.

We are currently working on the chemistry of the process in an attempt to understand exactly which long chain fatty acids are being removed by the process and what other, if any toxins are being removed. Results from further trials will be posted on this website as they become available.