Treatment and product recovery from wine lees, the sludge-like sediment left behind when wine or juice is transferred from one tank to another, is one of the biggest challenges facing the wine industry. The desire to minimize winery waste volume, coupled with legislation that limits the disposal of unwanted by-products, has made the lees issue even more important to producers.

Koch Membrane Systems (KMS) crossflow membrane filtration (CMF) technology has led to an improved method for recovering valuable wine and juice from lees. This novel process entirely eliminates the need for diatomaceous earth (DE) and other filter aids currently used with traditional recovery techniques. Crossflow microfiltration membranes configured in a multi-tube modular geometry are ideal for clarifying lees. The tubular design is well-suited for processing streams that contain high levels of suspended solids such as juice and wine lees.

Wineries using CMF systems are recovering wine of higher quality and therefore higher value when compared to traditional systems. Higher value wine plus significant annual operating cost savings are providing wineries with an attractive return on their investment.

During the winemaking process, insoluble solids are generated that have to be removed before bottling. These solids include fine fruit particles, tartrate salts, spent yeast, bacteria and soil and debris carried over with the fruit. Also, fining agents are frequently added to the wine, and contribute to the volume of settled solids. Fining agents may include bentonite, gelatin, silicasol, albumin, activated carbon, and polyvinylpolypyrrolidone (PVPP).

All of these solids eventually settle by gravity into a sludge-like material that is generically called lees. Wine producers generally classify lees into two categories: "sweet lees," also commonly called "must lees;" and "fermented lees," also known as "wine clarifier lees." Sweet lees are the settled solids typically found in white grape juice and often are further processed to gain higher yields, while fermentation lees consists of all sediment remaining after fermentation and fining. On average, about 10 percent of the initial volume is removed as lees which still contain a high percentage of recoverable juice or wine.

Wine recovered from lees using traditional techniques - rotary vacuum or plate filters - often is of low quality and may require further processing before being blended into a usable product. Lees are often accumulated from several batches of wine before being clarified in order to maximize the efficiency of traditional recovery. These older processes can result in oxidation of wine, yield loss and higher operating costs.

When using newer crossflow membrane filtration technology, producers can efficiently recover quality wine from the lees that is comparable to wine filtered on the main wine crossflow filtration system. The automated or manual CMF equipment is simple to use, less labor intensive, and increases yield while reducing by-product disposal costs.

Most wineries employ some means to get the maximum recovery from juice "must." The typical methods of separation include rotary vacuum drum filters, centrifugation and plate and frame filters. The recovered juice is unfermented and is usually recombined with the racked juice without affecting the must quality.

Once the must is fermented into wine, microbiological activity ceases and sediment collects on the tank bottom. If there is sufficient time, a very clear wine will result with very compact lees. However, this is seldom the case because wineries usually need to use the tanks for other batches and the wine is typically racked prematurely, resulting in relatively low-solids lees that contain a significant amount of valuable wine. This wine is difficult to recover from the lees, and is frequently discarded by small wineries. Larger wineries seeking to maximize yield normally use the same DE filtration devices that are used for must lees for further recovery.

In most cases, wines recovered using these filters are of inferior quality and can, at best, be used to blend into low quality, low priced wines. This is due to the long contact time with oxygen and the flavors imparted by DE, as well as some of the "yeasty" characteristics from fermentation. Much of this wine requires further processing, and ends up as a base for products such as wine coolers and flavored wine products.

Crossflow membrane technology uses highly-engineered, semi-permeable physical barriers that permit the passage of desired constituents based on size, shape or character. Membranes are available in a variety of configurations, materials and sizes. With crossflow membrane technology, a feed stream is introduced into the membrane module under pressure and flows over the membrane surface in a controlled operating mode. The selective barrier of the membrane separates the feed into a permeate and a retentate stream, both of which may be of value. While used for numerous purposes in many industries, membrane filtration in wine production is most commonly used to remove suspended solids and turbidity while allowing the passage of color, ethanol, flavor and aroma components. Other membrane applications for wine and juice include sugar concentration in must, volatile acid (VA) and alcohol adjustment, and color concentration and standardization.

Polymeric crossflow membranes, the type most often used in wine applications, vary depending upon the separation requirement and are provided in a number of different configurations including hollow fiber, spiral wound and tubular. Membrane porosity also varies with the application; the tightest is reverse osmosis (RO), through nanofiltration (NF), then ultrafiltration (UF) and finally, the most open, microfiltration (MF)

CMF, while relatively new, is an industry-accepted technology for wine filtration. However, until recently, the only method for wine and juice recovery from lees has been the use of traditional DE filtration techniques. Polymeric tubular membranes are often used for fluids with very high concentrations of particulate matter and, when constructed in a sanitary geometry, are ideal for lees processing. When CMF for wine clarification and recovery of wine and juice from lees are used together in a winery, the result is higher quality wine and higher yields. Figure 1 below shows an example of a typical crossflow microfiltration process for wine and lees filtration. All steps are low pressure (10-100 psig) processes that retain the suspended solids and pass all dissolved material below an average pore size range of 0.3 microns.

The CMF process for recovery of wine from lees has been used successfully by producers of both red and white wines and continues to gain in popularity. First and foremost, under normal circumstances, CMF maintains the wine’s important qualities, including acidity, aroma, color, flavor and clarity, with little or no oxygen pickup or temperature rise. Figure 2 shows a photograph of a pilot KMS lees recovery system now in use at a large producer of red and white wines.

Lees filtration with crossflow membrane technology offers a number of benefits to the wine producer, including:

The finished characteristics of the wine - color, aroma and flavor - are typically unaffected by the crossflow microfiltration process. Wine recovered from lees using crossflow membrane filtration maintains its desirable characteristics.

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