Removal of lees from underneath wine to reduce wine movements and tank cleaning
Abstract
Studies were performed to understand the sources and properties of winery lees. Grape solids were the largest source of lees and apart from red ferment lees, all settled lees flowed readily. Laboratory experiments were performed to study the possibility of removing settled lees out from underneath juice or wine. Experiments with 55° sloped cylindroconical tanks were somewhat successful, but experiments with a typical winery tank shape (5° sloped bottom from back to front) were unsuccessful even with the thinnest lees and with tank modifications. A workshop on lees and new lees reprocessing equipment was also convened at the 16th Australian Wine Industry Technical Conference.
Summary
Clarification is a major reason for moving juice and wine between tanks at wineries. After each movement, the source tank needs to be cleaned. Tank cleaning and the movement of juice/wine consumes labour, water and cleaning chemicals and generates wastewater. This project aimed to learn more about the sources and properties of winery lees. It also aimed to study the possibility of removing settled lees out from underneath juice or wine, such that the bulk of the juice or wine could remain in the same tank.
Samples of lees and information on lees volumes were collected from collaborating wineries and supplemented by laboratory experiments. Grape solids were the largest source of lees. In white wine production, these are removed prior to fermentation, while in red wine production they are removed after fermentation in combination with yeast. The other major source of lees was bentonite.
Most lees separated by settling were quite thin. The exception was gross red ferment lees. Gross red ferment lees samples exhibited high yield stresses (the minimum stress needed to initiate flow). This difference was not purely related to their relative solids content, as white ferment lees samples with similar solids contents exhibited low yield stresses. The difference likely relates to the inclusion in red ferment lees of grape solids and/or soluble materials extracted during fermentation on skins that are not present in white ferment lees. High yield stresses in red ferment lees were exacerbated by the inclusion of oak chips in samples from one winery. At that winery, oak chips were added to red ferments and were not all removed by their draining and pressing processes. These high yield stresses make these lees particularly difficult to manage in the winery. Alternatives to oak chips for colour stabilisation is an area that may benefit from further research.
A laboratory apparatus with changeable transparent tanks was constructed to study the possibility of removing settled lees out from underneath juice or wine. The use of 55° sloped cylindroconical tanks was somewhat successful in facilitating the removal of lees from underneath the clear phase, but this was not considered a practical option for large wineries as it would require the installation of new more expensive tanks. The use of winery-style tanks with a 5° slope from back to front with or without some simple modification was the experimental focus. With unmodified winery-style tanks, the clear phase quickly broke through the lees even with the thinnest lees. The use of a baffle above the tank sump just moved the location of breakthrough without materially improving lees removal. The use of a ‘Kreepy Krauly’ style device showed some ability to remove lees but continually moving the device to the location of the remaining lees presents major challenges and hygiene issues. The use of a sweeping arm on the floor of the tank was able to keep the lees moving and prevent the breakthrough of clears such that a portion of lees could be removed from the tank. However, this configuration would also require an expensive tank retrofit and as the lees level drops and the sweeping arm starts to break the lees surface it resuspended the remaining lees. Alternative means of agitating the lees while not resuspending it using devices that could be moved between tanks were explored unsuccessfully. Results from laboratory experiments were not sufficiently successful to justify the development of a prototype winery-scale device to facilitate lees removal from normal winery tanks.
A workshop on lees was also convened at the 16th Australian Wine Industry Technical Conference. This included presentations from wineries on their experiences with new lees reprocessing equipment. Slides from this workshop are included in Appendix A of this report. Several discussions were also held with wineries on the use of new lees reprocessing equipment during the project. A question raised by one wine company that had trialled a range of lees reprocessing equipment was how much of the downgrading that occurs with some lees reprocessing technologies is just a consequence of the juice/wine being occluded in different types of lees as opposed to the technology used to recover it from the lees. Further research to understand lees-occluded juice/wine interactions could be worthwhile.