Everything You Need to Know About “Thump Kegs”

Everything You Need to Know About “Thump Kegs”

There is enough misinformation about the thump keg to need some explanation to help moonshiners know what their best options are as well as to clarify exactly what a thump keg is.

The “Thump Keg,” or “Thumper Keg,” or “doubler” is a second chamber or distiller in the classic hillbilly still that essentially allows the distiller to double distill their output a second time, without having to rerun it through another still.

They are used to produce higher alcohol content moonshine. Where a single still is capable of producing 40 – 50% alcohol. By running that still a second time, you can increase that percentage.

The “thumper” is an additional piece of equipment positioned between the kettle and condenser. As part of a moonshine still, it is used in place of a column. While it might be considered “old-fashioned,” the thump keg is going through a resurgence.

Modern thumpers do not make the characteristic noise and are nicknamed doublers, although they do not actually double the alcohol content. They simply perform as a double distiller producing the same purity and increased proof as if you had separately put the batch through a second distillation.

How a Thump Keg Got It’s Name

The thump keg got it’s name from the sound made while you’re distilling. Most people thought the sound came from lumps or clumps of mash from your first chamber that enter the distilling column along with the vapor, make their way through, and land in the second keg, making a “thump” sound.

In actuality, it is the hot vapor erupting out of the pipe that periodically makes this noise. The low wine mixture is continuously heated by this hot vapor until it reaches the boiling point of alcohol. In the thump keg, this constitutes the second distillation, which produces the higher-proof alcohol than that which could otherwise be produced in a single run through the pot still.

Generally associated with the backwoods hillbilly still, the thump keg represents one of the cleverest design elements of a traditional still. Iconic, perhaps, the thump keg is a very old aspect of still design having arrived in North America along with European settlers. It is clear the use of a doubler, or thump keg, was well-known among the early colonists.

How a Thump Keg Works

The main purpose of the thump keg is to compound the distillation process, which is the process of evaporation that occurs when alcohol turns to vapor as the liquid mash is boiled. Alcohol has a lower boiling point than water, so it will turn to steam and get collected before condensing back into liquid form.

The thump keg usually holds both water and mash, or tails. As the pot still is heated, it gives off ethanol vapors, which travel through the pipe into the thump keg where it bubbles up through the contents already contained therein.

This is where it gets interesting: The vapor condenses where it heats the cold liquid that is already in the thumper. Simultaneously, a heat exchange occurs in the thump keg where the vapor cools.

There will not be any distillate until the temperature gets high enough for the compounds to vaporize. This has everything to do with the bubble size, the depth of immersion and the volume of alcohol in both the vapor and the thumper liquid. If your thumper is wide at the base, you may find it more difficult to produce vapor. This is why you tend to see more cylindrical thumpers to better facilitate this heating process.

While the kettle and metal piping used in the still are typically made of copper, the thump keg can be made of copper, stainless steel or wood. It is advisable to avoid glass, however, as this can be catastrophically dangerous should the glass break. If the thump keg is too small, the contents will heat up quickly enough, however the yield will produce a low percentage of alcohol. This is why the thump keg is usually charged with a high-alcohol content liquid, such as the tails from the last run.

Using the Thump Keg to Infuse Flavor

The thump keg can serve a dual purpose in your moonshine production. Not only does it serve well to increase the pure alcohol percentage, but it can also add a purer infusion of flavor, if you desire to flavor your alcohol. While most shiners add fruit to the mash or add the flavor to the finished product, adding it to the thump keg will steam extract the essences along with the alcohol during this second distillation process.

For some shiners, this is a mountain secret. Fruit infusion is a way to impart maximum fruit flavor without compromising potency. It could be fruit, herbs or even spices that provide a fresher, full-flavored robust whiskey. A well-managed pot still including a thump keg is capable of delivering the right volume of compounds that will carry over into the final product.

To get the most out of your thump keg, you should have:

Plenty of vapor to liquid contact, this mean a lot of small bubbles whether you use a screen or have enough pinholes at the end of the inlet tube.
A reasonable percentage of alcohol charged in the thumper liquid whether that is a small volume of mash or, better yet, some tails from the last run. Some shiners do not even add any water and, instead, only use the tails or mash.
A larger thumper, rather than smaller. A good rule of thumb is a 2:1 ratio – make the thump keg volume twice as big as the pot still. For example, to create 1 liter of spirits, make the thumper contents equal to 2 liters.

Sometimes, shiners want to know if a thump keg will work with their moonshine still’s column. These two components are incongruous. You would use a thumper instead of a column. This can be confusing when a complete moonshine still includes both, but you just need to keep in mind that it is a one or the other situation with these two pieces of equipment.

Another common misconception is that the thump keg is the same as a slobber box, considering their similar appearance in some cases. First off, the inlet pipe on the slobber box does not extend into the liquid, so there would be no way for it to bubble meaning there would be no distillation occurring. The slobber box simply provides a place for any foam or mash to be deposited so as to avoid it reaching the condenser. Sometimes, there will be a drain cock to facilitate emptying while the still is operating. The whole aim of a slobber box is to manage the waste by avoiding it reaching and contaminating the main spirits that are being collected. On a well-managed still, a slobber box is not even needed.

Hopefully, this information has been helpful in giving you the knowledge to understand what is a thump keg. Remember, the best liquids to use in your thump keg first are the tails from a previous run for the additional alcohol. Second, you can use some of the liquid you are about to distill. While not giving you as much alcohol volume as the tails would, it is still better than water. Water should be your last resort only because you are not going to get the “double-distillation” as you will with the other two options.

Sour Mash vs. Corn Mash: What is Better for Distilling?

Sour Mash vs. Corn Mash: What is Better for Distilling?

Aficionado or connoisseur, devotee or fan, those who understand the difference between bourbon and whiskey are already familiar with which is better for distilling.

Distilling whiskey involves the use of starchy grains, which are ground into a mixture, hence the term “mash.” The mash is then fermented before it is distilled, blended, and then finally aged. This is the point at which we can distinguish what separates bourbon from whiskey, despite the fact that most people assume they are one and the same.

While bourbon falls into the whiskey classification, not all whiskeys are bourbons. To be classified as bourbon, the grain mash used in distilling the whiskey must contain at least 51 percent corn and be aged a minimum of two years inside a new, oak barrel. Bourbon distillers typically have all the necessary materials to make new casks.

Another misconception is in thinking the term sour mash refers to the bourbon’s flavor, although it does have to do with producing a consistent taste.

Sour mash is a process. Sour mash distilling is akin to the process of making sourdough bread using a starter to achieve a consistent taste from one loaf to the next. By adding some of the spent mash, which is the previously fermented mash that contains live yeast, the home distiller is better able to control the yeast growth, thus producing a consistent spirit from one bottle to the next.

Both bourbon and sour mash whiskeys are descended from the moonshine that was originally produced in Kentucky and Tennessee. While connoisseurs may continue to debate over which is the superior brew, all would concur that they both comprise the distinctive American distiller’s craft. There are even societies devoted to the study of these uniquely American spirits.

Bourbon Whiskey is Made in the United States

Named for the French-Bourbon dynasty at the time, bourbon whiskey first began in territorial Kentucky. Blue Ridge Mountain distillers in both Kentucky and Tennessee managed to hide from revenue agents during the Whiskey Rebellion of 1791, which had everything to do with allowing the moonshiners to thrive in an unregulated industry. The successful production of these mountain distilleries eventually evolved into the refined bourbon and sour mash that famously hail from these parts today.

It was not until 1964 that the U.S. Congress ruled that bourbon whiskey is a “distinctive product of the United States,” and Federal regulation defines bourbon whiskey to include only bourbon that is produced in the U.S. Bourbon-makers do exist in other counties, however, only the bourbon produced in Kentucky is permitted the use of the name of the state on its labels.

The labels hold useful information to help you identify the whiskey. For example, by law, to be labeled Sour Mash Kentucky Straight Bourbon Whiskey, this bourbon has not been blended with other whiskeys, has been produced using some of the mash from a previous batch, which is the “sour mash,” and the entire product was made in the state of Kentucky.

While Tennessee whiskeys are produced using corn mash distilling, makers may only specify “sour mash” on the label if that process is used. These spirits may use the same bourbon recipe, but they are filtered through maple charcoal to achieve a different overtone. The strongest influences on the taste of bourbon are the grain, the yeast strains and the new, oak barrels. As well, even the type of wood used will contribute to the taste.

Both Kentucky and Tennessee are located where large limestone layers filter the water to a superb clarity for whiskey production and is considered by Kentucky bourbon distillers to be a signature element in their sour mash process. The predominant grain used to make all bourbon is corn, at least 51 percent. It is preferred for the sweeter, robust vanilla and maple syrup flavors that come from the sugars. Unlike the single malts made entirely from barley that come from Scotland and Ireland, rye, barley and wheat tend to be added to make up the balance of grain contained in the mash.

It All Starts with Corn Mash Distilling

Small Yeast Bubbles of Yellow Bourbon Mash with selective focus

It is generally thought distilling began in Kentucky in the late 1700s introduced by the Scots, Scots-Irish from the province of Ulster and others including the English, French, Germans, Irish and Welshmen. The possibility of identifying a single inventor of either whiskey or bourbon is unlikely.

Charring barrels for enhanced flavor when aging whiskey is a centuries-old practice in Europe. It was inevitable that this practice would migrate with the settlers.

Numerous counties were founded in the vast regions west of the Allegheny Mountains proceeding the American Revolution. Despite the region’s burgeoning growth, most people continued to refer to this area as Old Bourbon. As it happened, the main port in Old Bourbon where the whiskey was shipped was located on the Ohio River in Kentucky.

To indicate their port of origin, “Old Bourbon” was stenciled on the barrels. Like it or not, this strongly associated any corn-based bourbon whiskey with the name Old Bourbon. Most often, this was the first taste of corn whiskey most people ever had. In Tennessee, they prefer to call their bourbon “Tennessee whiskey” instead. The production process for both Kentucky Bourbon and Tennessee Whiskey are the same except that Tennessee whiskey is charcoal-filtered before going into the barrels.

Your Choice of Grains Influence the Flavor

Whether starting as whiskey or intended to be made into bourbon, it all starts with a mash bill that requires the minimum 51 percent corn with any cereal grain making up the remainder. Wheated bourbon is the result of using wheat in the mash bill instead of rye making it milder and smoother on the tongue. A higher rye content produces a dryer, spicy whiskey. The corn sugars produce a rich and syrupy quality and lends to a leathery finish as the spirit is aged. Craft whiskey distillers experiment with many different grains as accents to the corn.

Corn whiskey may either be unaged or aged in previously used barrels. You can really taste the corn influence in these whiskeys as there are little to no barrel flavors influencing the batch. If mash from a previous distillation is added to the corn mash to ensure consistency, then you have a sour mash. Most bourbons today are run off a column still that is then redistilled in a thumper. The clear spirit produced from this process is called “white dog,” which is placed in the charred new oak casks for the aging.

Sour Mash Distilling is Essentially Yeast Management

The yeast strains possessed by Kentucky and Tennessee distilleries have survived since prohibition with patents filed for their isolated yeasts. The primary purpose of the sour mash is the control of yeast reproduction with the pH balance being key to this process. Even the object used in this process are autoclaved to ensure no foreign element contaminate the desired yeast strain. The consistency of the batch depends upon this careful handling.

The sour mash process is much-praised for its ability to create an acidic environment for the yeasts. When prepared with fresh spring water as it is in Kentucky and Tennessee, its chemically neutral condition is neither acidic nor alkaline. With a pH of about 7, the yeasts cannot work correctly. It is the addition of the sour stillage, or mash, with a lower pH of between 5.0 and 5.4 that leads to the acidification of the entire mash. This brings the pH up to between 5.4 and 5.8, which is ideal for the yeasts to work properly.

Clearly, you can see the advantage to using sour mash when your goal is to achieve consistency in your white dog or if you intend to market your product as straight bourbon. The decision is ultimately yours, but at least now you have some knowledge as to the laws and regulations that come to bear upon how you identify your distillations.