Have you previously experienced difficult-to-filter wines?
Are you sure it was the wine that was difficult? Or, could your production practices lead you into a higher prevalence of filtration problems?
Let’s find out together.
Components in Wine
Most of us are familiar with the possibility of microorganisms in the wine. Wine harbors various yeasts and bacteria throughout the duration of its production. These microorganisms can be native to the fruit as the grapes come in from the vineyard, established in the winery (which can potentially be spoilage species), or manually added by the winemaking team during wine production.
Additionally, wine is composed of various chemical components that are dispersed throughout the liquid. These components, referred to as colloids, will vary in shape, size, and chemical property. Some of the more familiar colloids include things like sugar, proteins, polysaccharides, mannoproteins, pectin, gums (including things like CMC), and tannins. But various others exist, too.
If large enough in size, colloids will affect the turbidity of the wine. As new colloids are introduced to the wine, a rise in turbidity is often noticed. In contrast, during filtration processes like plate-and-frame filtration, a decrease in turbidity is observed between the feed (wine going into the filter) and filtrate (outgoing wine from the filter housing). (Note: If one doesn’t see a change in turbidity, that indicates a problem in the filtration process.)
However, some colloids are also very small and may not be detectable through turbidity readings. This is important in relation to the filterability of the wine. Colloids undetectable through turbidity readings can also cause filtration clogs or fouling, especially through adsorption properties associated with filter media. (Adsorption: adhesion of molecules to surfaces they come in contact. Definition, here.)
Understanding Filter Media and How Wine Passes Through a Filter
Filter media (i.e., the filter pads for plate-and-frame filters, cartridges for lenticular and sterile filters, or tubes for crossflow) are able to clarify wine by physically removing particular components and by separating colloids or macromolecules within a wine. However, the separation of such colloids is temporary.
That’s a whole lot of scientific jargon in two sentences so let’s break it down. (Pun intended!)
Most of us understand how pore size physically removes components from the wine. For things like tartrate crystals, microorganisms (yeast, bacteria), and anything that would be large or visual to the human eye, if the pore size within the filter media is larger than the physical component, that component will pass through the filter media. But if the pore size is smaller than the component, the component will get stuck in the media and not pass through the filter media.
This property is related to the “pore size” that is provided within the technical specifications of various filter media.
Winemaker be warned: for plate-and-frame filter pads and many lenticular cartridges, the pore size is nominal. This means that an average pore size is provided, but some pores are larger than the average and some are smaller than the average. For sterile filter cartridges (unless otherwise specified by the filter media supplier), the pore size is absolute. This guarantees a uniform size in pore size throughout the filter media. This is why the sterile filter is the last filter used prior to bottling: the 0.45 µm (micron) size will ensure that no yeast or bacteria can pass through the pore as they are both larger in size than 0.45 µm.
However, the other part of filtration, that is often overlooked by winemakers, includes the temporary separation of colloids as it passes through various filter media. This is why winemakers are encouraged to decrease the “average pore size” associated with the filter media in a particular filter run.
Colloids are uniformly dispersed in a liquid (in this case, wine). As mentioned above, the addition of any of these components to the wine results in an increase in wine turbidity. This is not unusual. As a new component is introduced to the mixture, until the colloid is properly stabilized, an increase in wine turbidity (even if it is not visual) can occur. As those colloids stabilize in the group of other colloids, turbidity usually decreases within the wine.
Colloids and Filtration
Some colloids will only interact with charges (positive or negative) that are associated with a filter media. If in high enough concentration, these interactions can lead to clogged filters.
For other colloids, the step-wise reduction in pore size within the filter media will help separate the colloids into shapes and sizes that can eventually get through the absolute sterile filtration step. This step-wise reduction in pore size is slowly breaking a part loose bonds affiliated with those colloids. While the bonds are broken, the colloids get smaller and smaller. However, as those colloids come back together, as bonds are joined, the colloids aggregate and get larger. The aggregation of these colloids can lead to physically clogging filters during a filtration.
Many wines will remain filterable for about 1 week (7 days) following the final filtration step in plate-and-frame/lenticular/crossflow filtrations. However, some wines will contain colloids that aggregate back together within a few hours, making the filtration process really challenging.
Because the aggregation of colloids is somewhat unpredictable, winemakers are encouraged to run filtration “quickly,” making sure to deduce the pore size of the filter media incrementally and within a reasonable time frame, usually 1 – 2 days. Furthermore, winemakers are encouraged to avoid delaying sterile filtration with the primary recommendation to complete sterile filtration in 1 – 2 days following the end of those pre-filtration steps.
Filtration Solutions for Winemakers
When it comes to filtration, it pays to understand the limitations within the winery that may inhibit key steps that could limit the efficacy and ease of filtration. The following lists several recommendations to improving filtration ease for your operation, noting that some of these investments can be made over time:
- Properly plan pre-bottling stabilization and filtration processes. I strongly encourage wineries to firmly write down a calendar of operations for each wine that is intended for bottling. Part of getting through filtration means allowing various components in wine and the added ingredients (e.g., tannins, gums, mannoproteins, sugar, etc.) the proper amount of time to better stabilize. If you need help with this, consider joining our DGW Elite Membership and bringing your wines and bottling times to me. I can write out calendars for you. Or, use the DGW Insider or Elite Memberships to review the proper timeline for stabilizing wines prior to bottling. This will help get the wine chemically prepared to get through filtration easier. Here are the timelines based on the following wine styles:
- White Wines (with Traditional Cold Stabilization Processes or the use of a Tartrate Inhibitor)
- Rosé Wine (with Traditional Cold Stabilization Processes or the use of a Tartrate Inhibitor)
- Red Wine
- Formula Wines (wines that require a formula submission to the TTB)
- Native Wine Grape Varieties (that are commonly difficult to filter)
- Invest in a turbidity meter. Measuring turbidity does help take some of the guesswork out of winemaking. While it provides some of the filtration solutions that I described above, it can also help with things like juice turbidity and bentonite fining trials for protein stability. Turbidity meters are very useful pieces of equipment, which I have explained, here. From a filtration perspective, measuring the starting turbidity of the wine can provide the winemaker with a better guess on which filter media to start with during the filtration processes. Over time, this can amount in winery cost savings both in terms of supplies and labor, as it reduces guess work associated with the filtration process.
- Develop standardized pre-bottling/filtration protocols. Some of the mistakes I see winemakers make with regards to filtration is timing wine ingredient additions properly and determining when to filter within the winemaking process (order of operations). Furthermore, winemakers often develop routine filtration regimes without really considering if the wine requires it or if the regime is effective enough for the wine in question. Using routine filtration regimes can become costly, especially if a winemaker is purchasing and using filter media that is not required by the wine. At DGW, I help winemakers develop a more standardized protocol for their pre-bottling operations, detailing a timeline for filtration operations. This quickly improves filtration efficiency, especially as the filtration operation becomes more habitual for most, or all, of the wines produced at a winery. In addition to using the DGW services to help create these operational guidelines, DGW Members and Clients can access the General Filtration Guide: Production Guide for tips on operating your filter unit, purchasing sterile filtration cartridges, storing sterile filtration cartridges, troubleshooting clogged filters, managing DO during filtration, and easing issues with difficult-to-filter wines. It pays to know what you don’t know when it comes to filtration, as a bit of knowledge can go a long way in improving filtration procedures for your winery.
- Use filtration enzymes for difficult-to-filter wines. Many filtration enzymes can get added in wines within a week prior to filtration and have positive effects on filterability. However, some wines that are more difficult-to-filter may require alternative enzymatic processing for an extended period of time to become filterable. When using enzymes in this manner, the order of stabilization and pre-bottling operations becomes extremely important to ensure the enzymes stay active in the wine through filtration.
- Consider filterability testing. Filterability testing assesses how a wine will behave under filtration conditions. This testing can help conclude the ease in which a wine can go through a sterile filtration unit. With difficult-to-filter wines, it may become essential to evaluate the filterability of the wine, in addition to the wine’s turbidity. Some wine labs offer this analysis for a defined fee.
This blog post was written with support from the following references:
ETS. Interpreting Filterability Results. Available at: https://www.etslabs.com/publications/publication/54
Peterson, M. 2021. Filtration FUNdamentals: a webinar on pre-bottling best practices. Available at: https://www.youtube.com/watch?v=l9rMLIgxEBg
Scott Labs. 2021. Best Practices for Successful Filtration Prior to Bottling. Available through their website.
The views and opinions expressed through dgwinemaking.com are intended for general informational purposes only. Denise Gardner Winemaking does not assume any responsibility or liability for those winery, cidery, or alcohol-producing operations that choose to use any of the information seen here or within dgwinemaking.com.
