Willamette Cross Flow

 

 

 

 

By no means a new technology, crossflow has been used extensively in the food processing industries since the early 1960s. Beginning in the 1980s, wineries began experimenting with the technology, but from the outset had serious difficulties, including: the equipment was prone to strip the wine and was difficult to operate, it would raise wine temperatures due to restrictive flow, and wine suffered from oxygen pickup. Finally, the excessive cost of the equipment made the technology prohibitive. Eventually this technology was relegated to low-end white wine production.

By the mid 1990s, this "borrowed" technology, which never fully adapted to wine, was rapidly losing favor. Except for large-scale production facilities, by about 2000-2001 crossflow filtration had all but disappeared as an acceptable winemaking tool.

Times have changed, however, and 2006 looks like a breakout year for crossflow filtration. Crossflow filtration manufacturers are taking serious steps to win back the hearts and minds of winemakers. Manufacturers have learned from past mistakes and have reinvented the technology. Far and away the single most important factor in this rebirth is the technical evolution of the filter membrane. Interestingly, it is not traditional equipment manufacturers driving this technology, but a few well-known filter manufacturers, who, by reformulating their membrane chemistry, have created new filters specifically designed for wine and crossflow systems.

Several membrane manufacturers are taking the unusual step of designing and fabricating their own proprietary hardware around these new filter membranes, resulting in well integrated equipment that is easier to operate and more compact. The best news of all is that by keeping everything in-house and designing specifically for wineries, the cost is dropping dramatically. In no uncertain terms, the small to mid-sized wineries are now the manufacturers' target market.

In many people's minds, crossflow is about to usher in the future of wine filtration. Nowadays we see crossflow realistically addressing important issues, such as time, labor, wine loss, problems with diatomaceous earth and quality of filtration, all important aspects to consider when choosing the crossflow system that will best suit your winery.

Crossflow in Use

"Crossflow is a solution looking for a problem," said Clark Smith, owner of Vinovation in Sebastopol, California, and suggests "the winemaker simply ask what they are trying to achieve." Crossflow is rapidly demonstrating it can handle almost any kind of filtration, from solids, to cold stabilization issues, to VA (volatile acidity) and ML (malolactic), not to mention stopping fermentation.

"We produce 50,000 cases of Muscat Canelli per year," said Alan Kinne, winemaker at Martin & Weyrich Winery in Paso Robles, California. "In the past we used DE filtration three to four times to stop the fermentation and to hold our wine at 7 percent. Now we make one pass with crossflow."

If there is one defining concept behind the cost-ratio benefit of crossflow versus traditional filtration, it is the expression "one pass." Generally speaking, plate and frame (pad) filtration will filter more wine per square meter of surface area than crossflow, but eventually the pads plug with retentate. Thereafter the process has to be repeated as many times as necessary, going from coarse to finer filtrations.

Crossflow is different. Almost all filter membranes in crossflow are rated with a nominal pore size of 0.2 microns. "Nominal" refers to the ability to filter retenate, generally 95-98 percent. "Absolute" rating is the ability to retain a problem suspension to almost 99 percent. NTU (nephelometric turbidity units) refer to the amount of suspended materials to be filtered; how cloudy the wine is. Crossflow membranes will reduce a wine's NTU measurement of 1,000 to 1; in effect, cloudy wine in, clear wine out. It is a continuous process, and ultimately the amount of wine processed will exceed that of a pad filter because you never have to stop to reconstitute a plate and frame; obviously the greatest savings result when filtering larger volumes of wine.

Naturally, the second most obvious savings is labor. By setting up one machine, with a hose in and a hose out, by one person, the savings can be substantial. Most machines today are automated to the point that you can literally set the parameters of the unit and walk away.

"Efficiency is our mantra," said winemaker Steve Anderson at Eola Hills Wine Cellars in Rickreall, Oregon (40,000 cases), "and we were having too many mistakes with standard filtrations. We wanted a simple system. Now I have an onboard flow meter so I can start the machine and go home at night. I simply make sure not to drain the source tank dry or overflow the receiving tank, and I'm done." One person, one set-up, one pass, and the wine is ready for a sterile filtration and bottling. And since most machines are totally self-contained, there are usually automatic cleaning cycles.

Being self-contained, the operation also reduces wine loss. Alan Kinne estimates that when pushing wine through three or four pad filtrations, the loss alone during cleanup and dripping can save hundreds of gallons of wine. Finally, with the simplicity of the equipment, a major bonus is you have a closed system that is hermetically sealed, thereby reducing the oxygen pickup to zero.

If offered the choice, most winemakers would probably never use DE again. Given the current environmental and worker safety issues related to hazardous materials and their subsequent disposal, crossflow again proves its worth.

Diatomaceous earth (DE)-most frequently sold to the wine industry under the World Minerals trademark Celite®-contains crystalline silica, which is an inhalation hazard, a known cause of silicosis and is classified by the IARC (International Agency for Research on Cancer) as a group I carcinogen for humans. Crystalline silica is chemically inert in the environment, however, making composting the most logical means of disposal. OSHA classes crystalline silica as hazardous, and respiratory and eye protection is recommended whenever working with open bags of DE. The U.S. Department of Transportation, on the other hand, does not consider DE to be hazardous, and the transportation of sealed bags of DE is unrestricted.

Local use and disposal regulations for DE vary widely. Some localities do not allow it to be dumped in landfills, others allow composting and others place no restrictions on disposal. It is safe to say that local and state controls will continue to become even more stringent. The cost savings of eliminating DE from your winery can be substantial: from purchasing, to storage, employee handling, respirator masks and final removal. In the words of Clark Smith, "Ultimately we arrive at an effluent-free winery."

Winemakers will always debate the effects pad or DE has on the wine. "Crossflow does not knock back the aromatics of wine like DE," said Ken Volk of Kenneth Volk Winery in Paso Robles, (10,000 cases). Volk continued, "If you have any issues with your wine, compared to any other type of filtration, crossflow is the most gentle." Kenneth Volk Winery is one of many smaller operations that is looking to soon purchase crossflow filtration equipment. For now, however, Volk is happy to take advantage of the growing mobile filtration business.

The best news is that the OEM (original equipment manufacturer) wants your business. Once prohibitive for the small operation, the cost of entry is dropping substantially. Manufacturers are realizing that with improved technology, it is possible to get smaller units into the hands of the winemaker for between $25,000 and $50,000. While these smaller units (fewer square meters of filtering surface) process less gallonage per hour, the automation makes the argument pointless. In addition to all of the aforementioned cost savings, the mere cost of a DE leaf filter, or plate and frame, can easily offset a substantial percentage of the purchase.

Crossflow Equipment

Crossflow equipment is relatively simple in operation and construction. Primarily we are looking at a circulation pump, assorted stainless plumbing and valves to direct the wine flow, filter housings (or modules or canisters) for the membranes, and varying levels of automation. The most basic units feature manual operation, but the addition of PLCs (Programmable Logic Controller) makes for nice compact units that require no supervision. Once the parameters of the machine are established by the winemaker, all a cellar worker does is connect the inlet and outlet hoses and hit the "start" button.

Currently, the smallest, fully automated cross unit has a single housing with a throughput of up to 300 gallons per hour. It features around-the-clock operation without supervision. It has an inert gas sparging and "pushing" system, and it has automatic "back flushing" to prevent build up on the 0.2 nominal membrane. Finally, it uses a monitored, variable speed circulation pump that equates inlet and outlet flow, reducing turbulence in the wine and minimizing temperature increase. The price is right at $50,000.

When one figures the cost of one of these units against filtration by other means, an optimistic cost analysis should find that, depending on the exact filtration method used currently, a 100,000-case winery should be able to cover the cost of a $50,000 crossflow filter in as little as one year. A 50,000 case winery should be able to do the same for a $25,000-$30,000 semi-automatic unit. One might argue that this one-year return on invested capital (ROIC) is probably a little on the optimistic side, but even half that rate still makes for an easy to justify capital expense with a ROIC of two years.

As the number of housings increase, so do the size of pumps and overall cost. Most manufacturers offer a range of units that start at two or four housings and can go as high as 25 to 30, filtering literally 6,000+ gallons per hour. At more than 50,000 gallons of daily filtration capacity, these large crossflow units are really best suited for the largest wineries. Some companies are positioned to engineer systems of whatever size or level of sophistication the customer desires.

The New Membranes

Crossflow membranes fall into three configurations: hollow fiber (polymeric), spiral wound (layered) or ceramic. Far and away, hollow fiber is the most common. Depending on whom you talk to, each membrane has advantages and possible disadvantages, and therefore winemakers are advised to research this one area carefully.

Overall, spiral claims to run at higher pressures but detractors suggest they clog easier. Hollow fiber runs at lower pressures, but can be expensive to replace. Ceramic was often considered the most expensive of all and brittle. We know, however, of a mobile service with ceramic that has logged plenty of miles bouncing down the freeways of California. (Membranes are usually guaranteed for about 10 years.)

Hollow fiber filters, also known as "organic," are comprised of hollow tubes sealed in casings. The wine passes through the center of the fibers, and the permeate collects in the outer casing. Spiral wound membranes are a mesh-like material sandwiched between two outer layers and then rolled into a tight spiral within a casing. Ceramic elements are called "inorganic" and are built of an extremely strong aluminum/titanium/oxide compound that is also used in medicine for bone replacements.

In addition, membranes are proprietary to the equipment, so it is (generally) impossible to mix and match one to the other: a Pall filter will not interchange with, say, a Koch.

Vendors now offer plenty of data focusing on membrane attributes, but the competition is growing so fast that the choices between filter elements may be based on something as simple as cleaning. We do know, for example, that ceramic elements can withstand higher concentrations of caustic and temperature. Based on the type of filtration being performed and the maintenance of the elements, filters will suffer more or less turbulence, greater or less flow, not to mention life span. Proper cleaning of the elements is critical; so like most equipment, if you take care of it, it will take care of you. Replacement costs can run from hundreds to almost thousands of dollars per membrane. Properly maintained, however, some winemakers report having filtered in excess of a million gallons without replacing a single element.

Going Mobile

Not unlike the phenomenon of mobile bottling, the wine industry is beginning to enjoy the same convenience and equipment savings from mobile filtration. Currently there are about three mobile filtration companies operating in California, and cost is on a per-gallon basis. Companies include: VA Filtration, Scott Labs and Winetech. Naturally the price is quantity-sensitive-the same for bottling-and the payback is beginning to come into focus.

When a winemaker factors in time, labor, material costs, environmental issues and quality of traditional filtration, the advantages of a mobile service are substantial. Similarly, if wineries eventually factor in the total number of gallons they filter per year (into the typical five-year term of an equipment lease with related tax benefits), it will not be long before more and more wineries opt to purchase a crossflow system.

"We have been the guinea pig for our family of wineries (Caymus Vineyards)," said Jon Bolta, winemaker at Conundrum Winery in Rutherford, California (100,000 cases), "and have been experimenting with mobile service. With the current competitive pricing within the industry, we will probably be buying a unit this year and expect it to pay for itself in one year."

In the meantime the mobile services afford the winemaker the opportunity to test the concept before making the commitment. Thereafter it is a matter of researching the equipment available.