Vacuum Distillation Feedstocks - Mash or Beer?
One of the beautiful things about distilling is that there are countless different paths one can take along the way to the end goal: a great tasting spirit. It all starts at the beginning though, with the mash. Distilling under vacuum opens up some exciting options otherwise not possible or not previously attempted (as far as I know). To understand our feedstock options though, it's important to first understand how they relate to the equipment we're using.
Copper. It's that magic metal that almost all distillers use and rely on. When I first got into distilling and started learning about it, I didn't understand why copper was necessary because my background knowledge was in brewing. But typical distilleries will distill immediately after a brief (3-5 days) period of fermentation. Depending on what materials are fermented (sugar cane, grains, corn, etc.) there will be different levels of sulfur and organo-sulfur compounds in the fermented mash. It's critical to remove much of this to improve the taste of the distillate. Copper loves to react with sulfur, as it will form complexes with it and therefore bind it up and remove it during distillation in the form of various copper sulfides.
Copper would be important to every distillation, presuming that the feedstock consists of materials that have only been mashed and/or fermented, and never boiled. But if the feedstock is produced in the same manner as a beer; that is to say, mashed, boiled, then cooled and fermented, then most of the sulfur is evaporated from the beer during the boil in the form of dimethyl sulfoxide (DMSO). Almost no distillers do this because it's not a traditional approach to styles, extra equipment is required, there is no need to isomerize hops for bittering and frankly most of the delicate aromatics and flavors from the hops and that developed during an extended fermentation with beer yeasts would be blasted away during distillation. However, vacuum distillation opens up the ability to capture these delicate aromatics and flavors, so it makes sense to consider a different approach to what you distill when using vacuum.
If your beer has been boiled in a kettle and had DMSO evaporated away, then you actually don't really need copper at all in your vacuum still (or presumably in your standard still). However, some copper is a good idea to include for other reasons. The main one being that it is a phenomenal conductor of heat. Having copper in some key locations may also have an impact on the final flavor and character of the distillate, but I haven't seen any appreciable change one way or another. I use copper in my heating and condensing coils, on my stripping plates, and in my packed rectifying sections. Everything else is stainless steel. Stainless steel is more durable, easier to clean and looks good in its own right, although it certainly does lack the warm, comforting glow of a copper still!
Many distilleries take the entire fermented mash, grains and all, and throw it in their pot still for distillation. This approach is not really viable, nor recommended, to the vacuum distiller. Doing this requires stirring, and although it can be done under vacuum with the right kind of stirring motor, shaft and sleeve arrangement, it's very difficult to do this at scale without expensive equipment. Rotary evaporators are one way to do this kind of a distillation under vacuum, but the larger these get, the more cumbersome and expensive they become. It's an extra layer of cost and complexity that has no perceivable benefit that I can fathom.
Distilling a filtered (solids removed) beer is a preferred option, in my opinion. And, in fact, it doesn't necessarily need to be filtered at all. Drawing a beer from a brite tank at a level above the settled trub is as good as any other method, and far less complicated and cheaper than filtration.
Since using vacuum opens up the possibility of capturing all kinds of delicate character that would otherwise thermally degrade or be chemically altered, then one can experiment with all kinds of beer flavors, yeasts, hops... the sky is the limit! By approaching the feedstock as really the most important "creative" aspect of the whole process, and the distillation as more of a technical necessity, then you can start to understand how vacuum distillation opens up a whole world of possibilities otherwise not available to the distiller. Heavily dry-hopped IPA? Yeah, you can distill that and it will smell and taste just like the beer. Sour beer? Yep, you can do the same with that. Any beer style or fermented "thing" you can think of, you can probably preserve that in your end product.
The key thing to keep in mind here is, good in = good out. If you start with garbage, you'll end with garbage. You could probably barrel age that garbage to smooth it out and end up with something great, but why bother? Well, actually that might be worth exploring now that I think about it...
Another important factor of the feedstock is alcohol content. This opens up some other possibilities to the vacuum distiller versus the brewer/distiller. Since the beer is at the heart of what the final spirit will be, we need to approach distilling with the mind of a brewer. Although it's important to note that things that are extremely important to the brewer, such as carbonation level, mouthfeel, alcohol content, general drinkability, etc. really do not matter at all to us. We can wing it in a way that a brewer simply can't in order to create the flavor profile we want. Since drinkability characteristics of the finished beer are not important at all, maximizing alcohol content becomes far easier. Once we have a beer mash and profile decided on, we can simply add sugar or max out the malt to the ABV limitations of the yeast we're using. And since we're talking about it, it makes sense to use a high ABV tolerant yeast. Many of the newer kveik type yeasts have very high alcohol tolerances and interesting flavor profiles. We can experiment with yeast freely because we don't have to consider many aspects of the beer when building our recipes.
Likewise, adding things to the fermenter is another option. Dry hops, coconut, fruit, cocoa nibs, spices, whatever you want to carry through to the whiskey(-like spirit), you can throw it in there. Distilling under vacuum will preserve a significant amount of the character of these things, as well as unique aspects of the yeast used and the mash. Of course, it's important to consider what the final composition will be and to make sure it is balanced. If there's too much cinnamon or nutmeg thrown in there, you might end up with something that just doesn't taste good. Just because we can make something taste crazy, doesn't mean anyone will want to drink it more than once, if ever.
While there are certain traditional routes that can be copied over to vacuum distilling, such as distilling the whole mash, using copper equipment, or starting with a filtered mash, the possibilities afforded by distilling under vacuum are worth exploring to create altogether new flavor profiles. Why work around the edges of trying to create a great whiskey in the same way everyone else is, when we can do something altogether new?! If you're using this method already, or considering it, we might as well go all the way down the rabbit hole and see what's on the other side! I'll be there waiting for you.