Wine Filtration Basics

By: Alyssa L. Ochs  

Filtration is a technique that winemakers use to clarify wine and remove sediment and haze. Through one of several processes, filtration prevents wine from appearing cloudy and re-fermenting in the bottle. It’s typically done using membranes or pads, but there are various methods that wineries can use to achieve their desired flavor and appearance. Therefore, it’s essential to learn about the basics of wine filtration, including methods of filtration commonly used, maintenance and cleaning considerations and tips for choosing a filtration system that works best for your winery.

The Purpose of Filtration

  One primary reason winemakers filter their wine is to make it look and taste more polished. Filtration also improves the microbial stability of wine, which prevents premature spoilage that makes a wine undrinkable. Typically, white wines are filtered to give them clarity. Some red wines are not filtered because they are better at absorbing off-aromas and flavors. This leads many winemakers to only filter reds when necessary and no more than truly needed.

Types and Methods of Filtration

  Filtration methods vary among wineries based on facility size, budget and wine quality. The most common methods of filtration used today are gravity-feed and pressurized systems. Gravity-feed filter systems offer coarse filtration, are affordable and ideal for small quantities of wine. However, these systems cannot effectively do very fine filtrations. Enter pressurized filter systems, which offer faster processing times and finer filtrations, making them more favorable among larger wineries. Unfortunately, pressurized systems also come with a higher price tag.

  Peter Wojnarowicz, President of Filter Process & Supply in Monmouth Junction, New Jersey, told The Grapevine Magazine that the method of filtration depends on a couple of factors. He said that the size of the winery is the most important factor, followed by the winemaker’s preferred method of processing. Filter Process & Supply started working in the craft beverage market over 10 years ago, giving them the insight and experience to explain each system’s pros and cons and find the right one for your winery.

  “Larger scale wineries use more crossflow systems, followed by the filter press, then lenticular (stacked disc). Rounding out the last method, small mom-and-pop wineries may use a cartridge-based system,” Wojnarowicz said. “Filter Process & Supply can provide all four types of filtration. There are advantages and some disadvantages of the four methods.”

  Filter Process & Supply works with established wineries and start-ups and has a consultative approach that helps people understand that filtration does not have to be a headache, even though it can be at times. 

  “After the set-up and training, our customers become more comfortable in filtering,” said Wojnarowicz. “Our goal is to process the entire batch without replacing filters, as that not only wastes wine but also time.”

  The type of filter pad used during filtration is also something to consider. Filter pads are rated by microns, and each type—coarse, medium and fine—has a useful purpose in winemaking. Coarse pads help polish a wine without making it lose its color or body. Medium-micron pads are a standard, all-purpose pad that will only take a limited amount of body and color out of a wine. Fine pads can remove 80% or more of leftover yeast and sediment and are best used after filtering through a medium pad.

  Depth filtration is a process in which wine moves in a perpendicular flow towards the filter, allowing clean wine to pass through after particles get captured within. These particles build-up, causing pressure in the filter to increase and flow rate to decrease. Once the filter reaches a termination point, the winemaker must clean the system before continuing to use it. There are a few different forms of depth filters used for making wine, including pressure leaf, plate and frame, cartridge and lenticular.

Filtration Strategies and Steps

  There are different times in which a particular filtration type makes more sense than others. The smallest particles in wine are colloidal or precipitated proteins, which are about 0.2 to five microns, compared to yeast and bacteria that are in the 0.65 to three microns range. Grape solids and fining agents can be hundreds of microns in size.

  The first step in this process is pre-filtration, which involves removing the larger particles in suspension. Often this method includes filter pads with diatomaceous earth. These same products can be used to polish wine after this initial phase.

  The next stage moves wine through a sheet or module filtration process to reduce yeasts and bacteria. Finally, sterile filtration with a 0.45-membrane cartridge is performed after the wine is made as clear and bright as desired.

  Crossflow filtration is a technique that was first developed for the food industry in the 1940s and has become popular in winemaking in more recent decades. Developers have created a new membrane that works better for wine, increases flow rates and makes systems more automated and easier to clean. For wine filtration, the common types of membranes are hollow fiber, spiral wound and ceramic.

Filtration Maintenance, Replacement and Cleaning

  Not only is it important to learn about the different methods and processes of filtration, but also the best practices for cleaning those systems and keeping them working. One tip to remember is to store unused filter cartridges in a clean and dry environment. Always follow the manufacturer’s instructions for proper rinsing and cleaning a filtration system after use. Organic matter can stick to the surface of the membrane and clog the filter in an undesirable way if it’s not cleaned and sanitized well. 

  The filter equipment cleaning process involves pumping with an adjustable flow that can be back-pressured and withstand temperatures of around 125 degrees. PBW cleaner, a non-caustic cleaning product made with alkaline, is often used along with SaniClean or StarSan products in large buckets. Set the filter up to soak, purge the filter, rinse with hot water and acid rinse with SaniClean for the best results. Since each filtration system is a bit different, it’s best to check with the company where you purchased the equipment to inquire about the availability and cost of replacement parts.

  “We take the approach that all contact surfaces with wine should be kept clean and sanitized,” said Wojnarowicz. “Sanitizing before use is highly recommended. I have seen customers using the same barbed tri-clamp hose for years and kind of cringe knowing that the hose was clear braid, and now it is discolored beyond recognition, and you cannot adequately clean into the barbs. Fitted hoses are better; however, the lifecycle of hoses should be monitored.”

Common Filtration Mistakes

  Wojnarowicz told The Grapevine Magazine there are a few common challenges for wineries, especially when there are too little filter media with too much flow. 

  “For filtration in general, we size for a two psi or less clean pressure drop,” he said. “Flow rates and pressure differential will vary depending on how coarse or fine the porosity of the media is. With cellulose media, the clean pressure drop is typically higher, between five and 10 psi after wetting out. Generally, the higher the initial pressure, the shorter the life of the filter.”

  Another common mistake that Wojnarowicz has noticed is the inadequate conditioning of the filter media sheet or pad.

  “I have seen wineries use the pads and stacked disc right of the box with no rinsing or conditioning,” he said. “Conditioning with citric acid recirculation helps remove the initial wet cardboard taste associated with cellulose. After a 20-minute recirculation, flush with an adequate amount of fresh water, and the taste should be neutral.”  

Choosing a Filtration System

  Every experienced winemaker has a preferred way to filter wine, which is one of the many reasons why winemaking is more of an art than a science. Before purchasing a pump-based system for filtration, vintners might want to see if the product is available to rent. Wojnarowicz said they will typically pilot-trial equipment on a rental basis so the customer understands what is involved.

  Determine the capacity needed for filtration and talk to filtration companies about what types of systems can best accommodate that volume. Since each filtration pad rating is useful for different levels of clarification, wineries may benefit from keeping multiple pad types on hand.

Pumps for Filtration

  Pumps are an essential part of the filtration process, and winemakers should work with companies that can guide them towards the best pumps to use for this purpose.

  “If a customer has an existing pump, we incorporate the pump into the process as long as it makes sense,” Wojnarowicz said. “We have the ability to provide equipment for both large and small wineries. While the pump can matter, rubber impeller pumps are the most popular. Positive displacement pumps work well, as the flow tends not to decay as pressure builds. I do not care for diaphragm pumps due to the pulsing, which interferes with a stable gauge reading. Pulsation also disrupts the particle build up on the filter and can force irregularly shaped particles through the media.” 

  Filter Process & Supply recently became an East Coast distributor for Francesca Pumps after meeting with their North American representative at an Iowa trade show. Functions of this pump include pulling a vacuum from 8.5 meters, running dry for 90 seconds without damage, having a pump panel programmed for spraying the cap as many times as necessary, and not de-gassing wine due to excessive suction. This pump also has an optional function for filling barrels without fear of overflowing and pumping whole grapes from the de-stemmer into the fermenter.

Current Filtration Trends

  As with many aspects of winemaking, some filtering methods and processes are currently trending with winemakers. Fining is sometimes used as an alternative to filtration because it is a more affordable way to get control over tannin profiles while also achieving heat stability. Crossflow technology and new lees recovery developments are trending because of the energy efficiency potential. For example, crossflow filtration methods now have lower water consumption and waste production, are more resistant to heat and chemicals and have lower polysaccharide and polyphenol absorption.

Wojnarowicz said that the primary trend his company has seen is the use of backwashable media. However, while he agrees that backwashable media is cost-effective for use in the beer market, wine is another matter.

  “I would hate to recommend a backwashable media to a winery and find they stored the lenticular media for three months, then found it had odors and mold growth throughout pore structure,” Wojnarowicz said. “Even if stored based on the factory instructions, cellulose media is an organic, and organics can decay and pick up minute flavor notes. Pall Filters is a big promotor of backwash media for wine, but from what we have seen and discussed with knowledgeable industry personnel, why risk using a previously used depth filter on a flagship wine? I am not saying it cannot be done, but not everyone will re-condition media correctly.”

Filtration Tips and Advice

  Among the many best practices for wine filtration are to rinse the filter with clean water before the first use and always sterilize the filter materials with hot water. Make sure to follow the product specifications for the specific filtration system you choose and keep up with regular maintenance. Also, understand that filtration has its limitations when it comes to wine because merely using a filter won’t make a cloudy wine clear or drastically change the flavor profile to something it wasn’t meant to be.

  Wojnarowicz said that when reviewing a start-up or existing winery’s filtration goals, the gentle impaction of wine on the filter media will yield a larger throughput compared to pumping as fast as possible to get through the process. He also said the correct sizing of the pump and the filter media are crucial.

  “As a general rule, we recommend about one-half to one GPM per square foot of filter media,” he said. “You can certainly go two to three GPM per square foot or more, but the higher flow will compact the solids and pore structure, shortening the media life. Most 40-plate filter presses have one-inch ID on the piping, so flowing 15 to 20 GPM is about the maximum we recommend. The surface area and micron rating typically dictate flow recommendation.”   

  Wojnarowicz also said that the type of pump can also affect the wine. 

  “The suction side of the pump can de-gas wine, which degrades the wine,” he said. “There are sensors available to alert the operator of too much suction. If you are using a clear hose, the bubble formation in the hose can be the telltale sign.”

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