As the old marketing saying goes, “consumers shop with their eyes,” and nowhere is that truer than in the liquor aisle.
The beautiful crystal clarity of a spirit helps to drive sales, better for marketing than any Super Bowl ad. That’s why it’s important for you as a distiller to understand the different types of filtering you can apply to spirits and the pros and cons of each method.
Charcoal
Charcoal filtration is the first type of filtration that you need to know.
Despite the name, charcoal filtration is less a type of filtration than it is a type of purification. That’s because the charcoal removes unwanted flavors and colors rather than making the spirit clear of unwanted particulate.
Charcoal filtration involves the use of a special type of charcoal known as activated carbon. Activated carbon can be made of almost any carbon-rich material, but for distilled spirits, this is most commonly coconut husk. To make activated carbon, its producers heat the material to an incredibly high temperature in a low-oxygen environment; this drives off volatile compounds and produces a porous charcoal that’s completely devoid of moisture. They then sieve the charcoal to isolate specific particle sizes; they may even grind the larger flakes to increase the available surface area and ensure uniformity.
To charcoal-filter their spirits, distillers often use a dedicated tank or housing that contains activated carbon. They then slowly pump the spirit into the housing, either from the bottom or top, typically recirculating the liquid for a set amount of time; or they may also send it to a catch tank for further processing. For very large operations, distillers often use multiple filter housings in a series, to allow individual housing downtime and increase throughput. This is partially because activated carbon—while it can be used multiple times—does eventually exhaust its ability to remove particles, and then it either needs to be rejuvenated or replaced. That’s why it’s important that distillers design their charcoal-filtration equipment for easy removal and replacement of activated carbon.
Each distiller must decide how much flavor and color should be removed via charcoal filtration. Time and the proof of the spirit are among the factors that determine the method’s impact. Typically, activated carbon has the biggest impact on lower-proof spirits and with higher residence times—though that’s not always the case, and it often takes trial and error to determine which methods work best for a specific product.
Distillers commonly use charcoal filtration for spirits such as vodka and gin, using it to remove unwanted color and help soften the harsh flavors of fresh distillate. For aged spirits such as whiskey and brandy, charcoal filtration is rare—it easily strips away the nuanced flavors and color produced by the barrel. One notable exception to this standard is rum, for which producers use charcoal filtration on barrel-aged rums to strip away color, so that the rum can be sold as white rum. Indeed, one of the most popular white rums on the market—Bacardi—ages in oak barrels before charcoal filtration strips its color and smooths its flavors.
Standard
The second type of filtration that you need to understand is standard filtration.
This refers to any type of filtration that’s designed to remove particulate from a spirit before further processing or packaging. There are several different types of standard filters, and it’s common for distillers to use a combination of these to achieve their goals.
Bag Filtration
Bag filtration is a standard type found in many distilleries. As its name implies, this method involves the use of a mesh bag, which is placed into a column housing to act as a catch for particulate. The distiller pumps the liquid to be filtered into the column from the top, and gravity draws it down and through the bag before it exits at the base of the column.
Most bag filters are made of silicone mesh or muslin, and they’re not capable of particularly fine filtration. Also, because they use gravity as the primary motive force, bag filters can be relatively slow, and they’re prone to clogging.
The main advantages of bag filters are that they’re cheap and that they can handle large solids that would pose a problem to other types of filters. For that reason, distillers often like to use them as a first step in the filtration process—especially when dealing with spirits that have been infused with whole fruit or spices.
Plate-and-Frame
Plate-and-frame filtration is perhaps the most common type of standard filtration found in most distilleries, and it’s often the primary filtration step for most spirits.
Plate-and-frame filtration involves the use of specialized sheets of bleached cellulose, often impregnated with zeolites and other resins to increase their filtration capacity. These sheets fit between plastic or stainless-steel plates, which align horizontally on a set of rods to create a depth filter with chambers for filtered and unfiltered liquid.
To operate a plate-and-frame filter, the distiller must tighten the plates together—often with the aid of a screw-press—to create a watertight seal between the filter pads and plates. They then pump the liquid into the inlet port, thus forcing it through the filter pads into the catch chambers, which then drain out the outlet port. That process continues until all the liquid has been forced through the filter pads—or until a measurement of differential pressure between the outlet and inlet signals that the pads are clogged and need to be replaced.
The main advantage of plate-and-frame filters is that they’re flexible while still offering excellent filtration outcomes. Distillers can easily modify the filter’s rate and capabilities by adding or subtracting plates, and the many different types of filter pads available mean that they can be used in almost any situation.
The main disadvantage of plate-and-frame filters is that they can be somewhat time-intensive and complicated to assemble—and, because of how they’re put together, they’re often associated with increased product loss and leakage. Regardless of those issues, plate-and-frame filters have become the standard at many distilleries. There are even now activated carbon–impregnated filter pads that allow plate-and-frame filters to accomplish both charcoal and standard filtration.
Cartridge
Cartridge filtration, meanwhile, uses premade tubular filters that fit into specialty housings that are designed to let liquid pass through the filter as it’s pumped through a system.
Like plate-and-frame filter pads, cartridge filters are often made from bleached cellulose—though they can be made from many different media, and some are specially designed to target specific compounds or particles.
Distillers who use cartridge filters often do so to provide final in-line filtration of spirits on their way to packaging—they’re sometimes called polishing filters. The main reason to use cartridge filters in final packaging is that they’re very effective at filtering out particles smaller than 100 microns (µm). That’s important because 10 µm is roughly the size of the smallest particles that are still (barely) visible to the average human eye; thus, cartridge filters can help to make spirits appear crystal-clear.
The main disadvantages of cartridge filters are that they easily clog and they can be expensive to replace. For those reasons, most distillers don’t use cartridge filters as primary filters, instead reserving their use for packaging.
Absorption Clarifiers
Finally, although this isn’t a true filtration technique, it’s important to mention that some distillers like to clarify their spirits using absorbent clarifiers such as bentonite clay.
When added to spirits, these clarifiers use their inherent ionic charge—either negative or positive—to attract proteins and other haze-inducing particulates, forcing them to fall out of suspension in a process known as flocculation. Distillers can then carefully rack off the clarified spirit for bottling, being sure not to disturb the sediment layer that will have formed.
Unfortunately, this process often leaves a considerable amount of spirit in the sediment, and it’s widely considered to be an inefficient process.
Your Objective Is Clear
Producing beautiful, crystal-clear spirits is one of the most important things distillers can do to ensure that their products stand out among the competition, and there are a variety of ways to affect a final spirit’s look and flavor.
As filtration technology continues to advance, there are sure to be new tools and methods that allow distillers even more control over the final color and clarity of the spirits in the bottle—thus influencing the shopper’s ever-important first impression.