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October 2015 P R A C T I C A L W I N E R Y & V I N E YA R D 63 W I N E M A K I N G Conclusion and recommendations It is evident in our small-scale study that the gushed bottles of wine were tartrate- unstable and had retained yeast lees sedi- ment from either incomplete riddling or lack of adequate time in the neck freezer prior to lees sediment removal. Riddling during winter is difficult unless the riddling room is heated. The yeast becomes sticky and clings to the glass and often forms such an even film that many people do not see it. Checking at the neck freezer to ensure a firm lees plug before bottles are transferred from the neck freezer to the conveyor belt that takes them to the disgorging machine will minimize inadequate neck-freezing. After crown cap and lees sediment removal, some disgorging units will draw a small amount of wine from each bottle to make room for the dosage, and this wine is temporarily held in a vessel. If a bottle is low-filled after dosing, then some of the vessel-held wine is used to top up the bottles. If any of that vessel- held wine has yeast in it, then each bottle that has been topped up could contain yeast, which might cause gushing after disgorgement. The overriding issue in this study was the impact of bottle variation. Although three bottles were used as replicates for chemical analysis, we suggest that future sparkling wine research should test at least five bottles as replicates to reduce the impact of bottle variation in the data. Bottle variation is impossible to elimi- nate completely, but attention to detail prior to bottling to ensure sugar is com- pletely dissolved (or the use of sterile fil- tered grape juice or liquid sugar instead of sugar crystals) and the liqueur de tirage is evenly and accurately added to each bottle can help. During bottling, winemakers should check that each bottle receives the same amount of yeast and sugar by monitor- ing tank mixing throughout bottling. Additionally, some winemakers sweeten the wine, then lightly filter it to the bot- tling tank (yeast is added later) to ensure sugar is dissolved before bottling. It is worth remembering that the posi- tion within a storage/riddling cage will impact bottle variation along with vintage variation, grape variety and production techniques (such as yeast with poor floc- culating ability or inadequate cold stabi- lization). We have developed a checklist guide to assist in the reduction of gushing for wine producers new to disgorging (Table 4). PWV Bottling handling and disgorging environment Wine composition Packaging materials Table 4. Remedial checklist for sparkling winemakers Ensure neck freezing, lees removal and dosage addition is not under UV lighting. Cover all windows and close doors to remove natural sunlight from entering the room. A warm room of 15° C with cold wine of 10° – 12° C will result in gushing. Aim for an ambient temperature and wine temperature of 12° C. Avoid disgorging in winter due to extremely low temperatures or in the middle of summer if the wine has to be moved from a different building or the disgorging area does not have tempera- ture control. Allow time for the wine temperature to adjust be- tween rooms with different temperatures. Careful handling of each bottle prior to disgorging out of UV lighting and with as little movement as possible. Ensure each bottle is at an angle when being disgorged and dos- age is added. Most machines now have this built in to prevent dosage entering straight down into the bottle and to allow it to slide down the side of the bottle. As part of the quality-control program, check that the sediment plug in the neck of the bottle is firm prior to opening. Vintage variation and grape variety will impact gushing poten- tial, but reducing its frequency can be achieved using techniques below. Ensure wine temperature, dosage temperature and ambient temperature are 12° C where possible (or at least the same temperature). Ensure bottle pressure is 6 atm or below. Check accuracy of sugar levels in relation to the desired pressure prior to tirage ad- dition at bottling. While there are other options for stabilization if cold stabilizing is chosen, seed the wine with a crystalline tartrate (potassium or calcium or combination) at -4° C. Ensure sugar has completely dissolved in the base wine and the liqueur de tirage before bottling it by constant tank stirring dur- ing bottling. Ensure sugar is completely dissolved in the dosage or use sterile filtered grape juice or liquid sugar if available at the correct sugar concentration prior to neck freezing and lees removal. Ensure yeast for second fermentation has good flocculating abil- ity. Consider using an adjuvant and check that the riddling pro- gram has moved all sediment to the cap. Ensure adequate time is allowed for each bottle in the neck freezer for yeast lees to freeze. Check that the lees plug is firm. Reduce phenolic compounds from juice prior to first fermenta- tion for white sparkling wine. Ensure that wine with high pheno- lic content (rosé and red wines) is riddled, neck frozen and lees removed at low temperatures under low light where possible. If MLF has not been conducted or is not required then consider sterile filtration of the base wine before bottling, ensure that the storage temperature for second fermentation is low. Bottle quality control: bottle design, shrink-wrapped, sterility and glass color. Cork quality control: Quality cork, dust-free corks and consider cork options. Acknowledgements The authors wish to thank Tawse Winery and David Munksgard of Iron Horse Vineyards for his suggestions and assistance. Bibliography For the complete bibliography for this article, please visit practicalwinery- library.com.