When shopping liquor-store shelves, consumers regularly judge bottles not just by their labels but also by the eye-catching qualities of the liquid within them. That’s why distillers work hard to ensure that their products aren’t just tasty, but also attractive to the eye.
To get there, many distillers turn to a specialized but sometimes controversial filtration technique known as chill filtration.
Before you can decide whether chill filtration is right for your spirits, however, it helps to understand exactly what the process is designed to counter.
The Ways of Haze
Haze—sometimes referred to as chill haze—is a catch-all term for the visible cloudiness that forms in spirits, typically after bottling.
There are many different causes for haze, but it’s often linked to the presence of compounds high in molecular weight, including long-chain fatty acids, esters, and ethanol-soluble lignins. When there are enough of them in a spirit, these compounds slowly cluster together to create a haze that can be seen with the naked eye, thereby distorting the spirit’s visual appeal.
The formation of hazes can be slow or rapid, happening over the course of weeks or months—or even in just a few minutes, appearing before a consumer’s eyes as if out of thin air. Certain factors can accelerate that formation—for example, if a spirit is proofed below 48 percent ABV, or if it’s chilled below 68°F (20°C). That’s why we often notice haze when a spirit is served diluted with water or when it’s been stored in a refrigerator or freezer.
While most haze has little to no effect on the flavor or potability of a spirit, many consumers consider it to be a defect—and that’s why many distillers counteract it with chill filtration.
Prepping for Chill Filtration
As the name implies, chill filtration is basically the practice of cooling a spirit down and filtering it to remove particulate. However, to successfully deploy chill filtration in way that prevents haze formation, it helps to be aware of some special considerations and methods.
First, to effectively chill filter a spirit, it should be proofed to an alcohol concentration that allows the maximum number of water-insoluble molecules to be pulled out of solution. That exact ABV is different for each spirit, but—generally—the lower the better. Most distillers understand that spirits above 53 percent ABV won’t properly chill filter, so they try to have their spirits as close to bottling proof as possible.
Second, the spirit also needs to be at an appropriate temperature before filtration can commence. There are many ways to chill spirits, but the most common method is to use glycol. The optimal temperature again depends on the type of spirit, as well as the desired level of filtration, but we associate colder temperatures with increased levels of filtration.
Typical temperatures for chill filtration range from 15 to 40°F (–9 to 4°C). It’s important to note that during the filtration process, the spirit sometimes fluctuates slightly in temperature because of the physical movement of the spirit. To account for that, many distillers develop an acceptable temperature range for chill filtration rather than specify an exact temperature.
Once you’ve sufficiently proofed and cooled the spirit, it often gets time to rest before filtration—typically 24 hours. That rest helps to encourage haze formation, allowing time for larger haze particles to form. Some distillers, however, skip the rest and begin filtration immediately, though that reduces chill filtration’s effectiveness.
Some Process Details
The preferred filter media for chill filtration are cellulose filter pads; they allow a large amount of customization, with varying thickness and retention rates that permit you to tailor your process to each batch of spirit.
Some distillers use cellulose pads with other filter media, such as diatomaceous earth, for chill filtration. However, that’s not ideal for aged spirits because these other media can remove color and texture from the liquid.
Chill filtration proceeds in the same way as standard filtration: by pumping liquid through the filter media at a consistent rate. That continues until all the liquid has gone through, or until there’s a high enough differential pressure that the filter media is deemed saturated and in need of replacement.
Once the process is complete, it’s time to test the spirit for taste and odor acceptance and to check its color and clarity against a reference standard, before allowing it to proceed to bottling.
What to Chill Filter?
Almost any spirit can be chill filtered, but because the risk of haze forming is lower at higher proof, most distillers focus their efforts on spirits bottled below 47 percent ABV.
Whiskey and rum are both commonly chill filtered because the compounds contributed by the barrel during aging increase a spirit’s propensity for haze formation. Bourbon, in particular, is at risk of forming hazes because fresh barrels contain high levels of insoluble sterols such as stigmasterol, which heavily contribute to haze formation.
Many gins, fruit brandies, and other botanical spirits are chill filtered to reduce the likelihood of haze, although the practice does run the risk of removing important oils for flavor and mouthfeel.
Because of the cold temperatures involved, distillers don’t usually use chill filtration on low-proof spirits or heavily obscured ones, such as canned cocktails and cream-based liqueurs.
Pros of Chill Filtration
Chill filtration offers several important advantages to distillers.
The first and foremost advantage of chill filtering spirits is that it greatly reduces the risk of spirits developing visual defects after packaging. That’s because even basic chill filtration can reduce haze-forming compounds such as ethyl palmitate and ethyl myristate by as much as 75 percent of their original levels—much more than standard filtration, which reduces such compounds by only about 40 percent.
What is more, chill filtration’s reduction in haze-forming compounds doesn’t come at the cost of flavor. Over the years, scientific researchers have consistently shown that both educated consumers and distillers are unable to tell the difference between properly chill filtered spirits and those filtered by other means. Indeed, in one of the largest such experiments, Horst Lüning of Whisky.com showed that there was no evidence that a group of 111 experienced whiskey tasters could consistently identify or rate differently chill filtered whiskey. That property makes chill filtering an important tool for distillers who are concerned about haze but want to preserve flavor.
Finally, one last advantage of chill filtration is that it’s relatively simple and straightforward compared to other filtration methods. It’s easy for both consumers and distillers to understand, and it’s often more economical, especially for larger distilleries.
Cons of Chill Filtration
Despite all the apparent benefits of chill filtration, there are some downsides.
The first downside is that—as with all types of filtration—it’s possible to overdo it to a degree that alters the product by removing compounds. That can have unintended consequences on the spirit, and it may even affect its quality, which can be problematic. When working with new or experimental spirits, it’s important to monitor chill filtration closely, especially if you’re working on a small-batch or single-barrel offering.
A second downside associated with chill filtration is that it can be energy-intensive and costly to set up. That’s because chill filtration often requires a dedicated tank and a large amount of chilling capacity to operate correctly. For craft distillers working in cramped spaces without any formal chilling capabilities, installing and maintaining the infrastructure for chill filtration could be cost-prohibitive.
Finally, perhaps the greatest downside to chill filtration is that it has a negative connotation among many consumers, especially whiskey aficionados. Many consumers believe that chill filtration removes flavor and texture compounds from the final spirit. Although that’s been repeatedly disproven (see above), the public perception of chill filtration has influenced many distillers to shy away from the practice.
Some Scottish distillers, such as Bruichladdich, have begun intentionally packaging their products at a high enough ABV to avoid haze formation, proudly advertising that none of their spirits are chill filtered.
An Effective Option
While chill filtration can be a contentious topic for some consumers, it’s still one of the best available methods to combat unwanted haze.
Many famous brands, including Johnny Walker and Wild Turkey, still opt to chill filter their products. The process helps to ensure that their consumers receive consistently brilliant whiskey every time.
Ultimately, as a distiller, you must decide for yourself and your own spirits whether chill filtration is the right process to lock that visual appeal into the bottle.