Explaining The Thumper Keg: The Basics

by Karl | Updated: March 31, 2021

If you’re someone who has zero knowledge about this and is hearing the words thumper and keg together for the first time, you might be thinking that this is what rabbits and bunnies use to party.

Don’t worry. We made this guide for the home distiller who needs to know everything about thumper kegs, what it does, what it’s for, its purpose, and how it works.

A Quick Summary

If you’re in a hurry and just need to know the most essential information about the humble thumper keg, here it is.

  • What Is It? A thumper keg works to distill your low wine a second time. It may be made of copper, steel, or wood, and sits between the still pot and condenser.
  • What Does A Thump Keg Do? It speeds up the distillation process and transforms your low wine into a liquid with higher alcohol content, which is critical for making moonshine or bourbon.
  • What Size Thump Keg Do You Need To Use? It should generally be about 25% to 40% of the size of your main boiler.

Now, if you need to know more about the thumper keg, keep reading.

What Is a Thumper Keg and Where Is It From?

A thump keg, aka. the doubler, thump barrel, or thump chest, is usually referenced along with the backwoods whiskey still. It has a very old, classic design.

Quick History Lesson

The prevailing theory is that early settlers brought this design of the thump keg along with them and incorporated it into the stills that they eventually started constructing once they’d, well… settled.

If you look around, some of the older European stills support this theory because they also made use of what looks like the same chambers that functioned as thump kegs.

This means that the design and ingenuity of how it works were already well-known to the colonists who came over from the British Isles!

During the Prohibition Era, bourbon distillers and moonshiners in the Appalachians favored using thumpers for their recipes [R].

The Thumper Keg of Today

Nowadays, the thump keg remains to be one of the most iconic and clever design elements of the traditional hillbilly still.

Anyone who makes moonshine will know how important this is for their moonshine stills.

The thumper keg can be made of copper, steel, or wood, and sits between the stillpot and condenser.

Why is that, you ask?

Simply put, its purpose is to distill the output of the pot still a 2nd time without having to run the distillate through the still again.

What Is a Thumper Keg For?

Still confused what it does?

We’re getting there.

So we briefly stated what a thump keg is meant to do. Now, let’s get into the details of how this works.

Ordinarily, a standard pot still that does not have a thump keg can distill a wash only to a “low wine”. This will give you an output that is 40 to 05% alcohol by volume or ABV.

If you want to achieve the high alcohol content for high-proof whiskey or any other spirit like moonshine, YOU WILL NEED…you guessed it!

A second or even a third distillation.

Now, a lot of distillers in Europe continue to use the swan-neck pot stills and a beer stripper to distill wash to the low-wine state, while using a second spirit still to transform it into a high-proof spirit.

In the case of hillbilly stills, the thumper keg acts as the second distillation apparatus, much like the spirit still.

How Does A Thumper Keg Work?

Now, you may ask yourself how this magic happens. Well, the way a thump keg works are extremely clever.

The thumper keg uses the waste heat emitted by the steam pot, making it a very efficient distillation apparatus in moonshine stills.

Let me explain.

  1. A standard still will heat the wash or fermented solution to a high temperature.
  2. This releases the alcohol vapors.
  3. These vapors are then captured by the condenser into the solution called low wines.

Did you know: Without a thumper keg, you will need to distill this liquid through various stills to achieve that high alcohol content. This multiple distillation process, while effective, is expensive and time-consuming.

The thumper keg simplifies the moonshine-making process, which is why more moonshine-makers prefer it.

So How Does It Work, Exactly?

Some moonshine distillers add additional ethyl alcohol into the thumper during these distillations to make a more potent liquid with a much higher alcohol content.

One of the things you need to do in your distillation process is to allow your mash to reach the boiling point. When it reaches this temperature, it will start emitting steam or hot vapor.

Now it’s basic science that steam has to come out somewhere (otherwise things will start going ka-boom and nobody wants that).

So, this steam will look for a way to escape, which means it will find its way out of your moonshine stills.

Here’s where the thumper keg comes in.

  1. As the hot vapor exits your still, it will pass through the arm into the low wine that’s already condensed in the bottom of the thump keg.
  2. You’ll start to hear a thumping sound as the vapor and condensed low wine erupt out of this pipe every so often. This is where the thumper gets its name. 
  3. By heating the liquid again, the thumper keg sends highly purified alcohol vapors from your still to the condenser. This thumper liquid is the high-proof spirit that all moonshine-lovers covet.

Pro-tip: the temperature is a great indicator of where you will need to make cuts to achieve the proof you want.

You see, the vapor’s temperature is fixed based on the ratio of alcohol to water.

By measuring the temperature of the liquid anywhere in your set-up, with or without your thumper, you will have a good idea of the proportion of alcohol in your mix.

Watch out for the mash you’re using. Remember to never let your mash boil over into the thumper!

The Result

The effect of this entire process is that hot vapor will continuously heat the low wine to the boiling point of alcohol, “distilling” it a second time.

This results in a high-proof moonshine, bourbon, or spirit you cannot get from a single run of the liquid through an ordinary pot still.

This is why moonshiners and other distillers prefer to use wood for their keg.

Wood has great insulation and is better than metal at keeping heat trapped inside to maintain this temperature, so moonshine distillers are sure the process is as efficient as possible.

The more heat there is inside the barrel, the better it is for your thump keg.

Infusing Flavors Using A Thumper Keg

We’ve already given you a pretty good idea of how a thumper keg works. But did you know you can also use it to add more layers of flavor to your moonshine? 

Before you start distilling, fill the thumper keg with a small number of spirit tails from a previous batch (best option), some wash from the current batch, or water (water is the last resort).

This is the thumper liquid and it is meant to COOL the vapor that comes in from your pot still.

If you want to infuse extra flavor into your moonshine, you can also add fruits, herbs, or spices at this stage.

You will have several options for doing this.

  1. Add fruit-infused spirits to your thumper keg – You can place your chosen fruits, spices, and herbs into a big container of low wines or head/tail spirits. Then, let it sit for about a week or two to gradually infuse these flavors into the liquid. Once it’s time to distill, just add this solution to the bottom of the thumper keg to impart its flavors into your final moonshine.
  2. Add juice or oils directly into your thumper – In case you want a simpler and faster process than the one above, you can also add liquid ingredients like juice (apple, lemon, peach, blackberry, etc.) and coconut oil directly into your thumper keg.
  3. Add raw ingredients directly into your thumper – Now this is a combination of the first two flavor infusion methods we’ve mentioned. You can choose to add fruit peel, herbs, spices, and mashed ripe fruit directly into your thumper keg. Just remember that in the case of mashed fruit, you will need to add large quantities to impart that flavor. Also, it can result in quite a mess.

Regardless of which method you choose, you need to extract the heads from the ethyl alcohol before infusion. This will make sure the flavors will infuse the distillate that you will drink.

How Does It Compare?

While the thumper keg is a step up from an ordinary pot still, don’t expect the same results as you would from running your vapor, water, and distillate into a sophisticated reflux column still.

The reflux column still can yield up to the theoretical limit of 95% alcohol by volume or proof, if it is well-made, while also giving you better separation of the ethyl alcohol, esters, and ketones in the heads, or the heavy fusel alcohol in the tails.

However, some distillers don’t prefer this because they say it strips too much flavor away from the distillate, giving you less tasty alcohol in the end.

Who wants that, right?! (**says the person who loves coffee**)

These purists prefer a thumper to maintain that flavor in your distillate, while still achieving the right alcohol by volume or proof. This is true, whether you are making moonshine or some other alcohol.

In the end, though, we recommend going for a thumper if you want to achieve that higher alcohol by volume or proof without having to run your distillate through a more expensive set-up.

We’re talking to you, home moonshiners!

What’s the Right Size of Thumper Keg?

As we’ve mentioned at the start of this article, a thumper keg should be 25% to 40% the size of your main boiler.

But if you are planning to prime your thumper keg with a big amount of charge, whether it be botanicals, low wines, wash, or water, get a thumper keg that is at least 50% the size of your main boiler.

How Do You Clean A Thumper Keg?

If you’re looking for the easiest way to clean your thumper keg so that it’s ready for making your moonshine, you will need to do a vinegar run.

  1. Just fill your boiler up to 20% capacity with a mix of 50% distilled hot water and 50% vinegar.
  2. Then, start distilling from your pot into your thumper, just like how you normally would when separating tails and distilling spirits.
  3. Let it reach a temperature of at least 170 degrees Fahrenheit and keep this going for at least 5 minutes.
  4. Once that’s done, turn off your heat source and let your distillation equipment cool down to a temperature that you can handle. Empty the vinegar solution, and you’re done!

Note that you only have to do this if you have a brand new thumper keg. Otherwise, just do everything 2 to 3 times a year.

Thumper Keg Recommendations

If you need to get a thumper keg and want some recommendations, this is for you.

Stampede Stills 2 Gallon Copper Moonshine Still Thumper Keg (Doubler)

A thumper keg that is completely made out of copper (20-ounce copper sheet). It can hold up to 2 gallons of liquid. It also comes with a half-inch ball valve drain and half-inch copper pipe handoffs.

HOWEVER!

If you’re looking for a thumper keg that is made of stainless steel, you can check out this for your pot….

DIY 2 Gal 10 Liters Thumper

It’s made of food-grade materials and high-quality stainless steel that is 100% lead-free for safe distillation. It even comes in various sizes!

Stampede Stills Copper Half Gallon Widemouth Mason Jar Thumper Kit [R]

Another great and affordable option if your purpose isn’t to make large amounts of alcohol.

It is a handcrafted copper tube and seals that can covert any wide-mouth mason jar into a thumper using its gasket and pipe.

Just note that it does not include additional pope or coupling unions to connect it to your setup.

Final Words

The world of moonshine-making is vast. This is just some of the information that will greatly help you along so you can perfect your moonshine. Have fun!

Lead marketer, brewer, dad, and husband. Pretty much an all-round awesome guy.