Why Limestone Water?

By Chris Morris

The use of limestone water in the crafting of great Kentucky Bourbon is legendary. Kentuckians grow up with that belief emblazoned in their psyche. This makes me ask -why? Why is limestone water so identified with Kentucky Bourbon? What is limestone water? Why did our ancestors use it to craft their Bourbon Whiskey in the first place? The answer to these questions, like those of our other articles, can be found in time and place. The use of water in the production of Whiskey is one of its sources of flavor. If you recall the global definition of Whiskey, every Whiskey must be made from cereal grain. Well, unless that grain recipe has been cooked, mashed or washed with water toremove its starch and sugars, fermentation with yeast cannot occur. So, water is a necessary ingredient in the crafting of any type of Whiskey.

What specifically is limestone water? Limestone water is naturally occurring water filtered through limestone rock, which is rich in calcium and magnesium and is iron free. Kentucky is famous for its “karst” region, its cave region. Famous caves such as Mammoth Cave have been formed over millions of years by water flowing underground through cracks in the limestone strata that underlie the Bluegrass Region, dissolving the limestone. This creates caves, sinkholes and of course, limestone water.

The legendary role that limestone water plays in the history of Kentucky Bourbon is fascinating. I have read articles written by professional journalists that actually state that the use of limestone water is required to make Bourbon, that it is part of the standard of identity of Bourbon Whiskey. The use of limestone water is not required by the federal government. The only type of water referenced in standards of identity is the use of pure water. So, no matter how much we may think that limestone water is a Bourbon requirement, it is not the case.

Let’s be clear, every type of Whiskey can be made with water that is not limestone sourced. For example, there are over 100 Single Malt Whisky distilleries in Scotland, but only one of them uses limestone sourced water. So, let’s put that one legend to rest; a distillery does not have to have limestone water to make good Whiskey. In fact, many Kentucky Bourbon distilleries do not use limestone sourced water today. The more modern operations are not purposely situated on a limestone spring water source because today they can rely on a municipal water supply. There is nothing wrong with that. As long as the water has been filtered and is iron free, it can be used. That last point is very important, if water has iron in it, it cannot be used to make Whiskey for chemical reaction reasons. 

Every historic distillery, and by that I mean pre-commercial distilling age, was located on a natural water source. As noted earlier, water is required for the mashing or cooking of the grain recipe and for other activities in a distillery. Therefore, a ready supply of water on hand was needed. 

While a creek or river would supply the amount of water needed for running a gristmill or for providing cooling water for a still, our ancestors knew that that water was not to be used for human consumption. Their livestock would stand in the creek, pond or lake and any runoff from their homestead would flow into the water. They knew from experience that the water was not safe to drink. But they realized that water bubbling out of the ground from an artesian well was going to be pure because its source had not been contaminated by environmental conditions. This was the water you wanted to drink and use in your Whiskey making process. 

The underground source of springs varies from across geographic regions, and in some cases spring water is not appropriate to use such as if it issues from an aquifer that contains sulfur or salt for instance.Fortunately, in central Kentucky many spring systems are fed by limestone strata. The water is iron-free and full of minerals such as calcium, magnesium, and potassium. These minerals are helpful in the production of Bourbon because they furnish yeast, which is essential in the fermentation process, with nutrients it needs to do an effective job. This mineral rich water, the soil and grass it contributes to, was also vital in the establishment and location of the thoroughbred horse breeding industry in central Kentucky. The same minerals in the limestone water that help a bourbon distiller’s yeast are also important in developing strong bones in thoroughbred horses, but that’s another story.

So, limestone water was used to craft the early Kentucky Bourbons not by design, but by opportunity. That was the water available to the early settlers of Central Kentucky, and with their knowledge of the environment, they knew that was what to use. Take the site of today’s Woodford Reserve Distillery as a classic example of this practice. The Elijah Pepper family settled on a hill overlooking the banks of Glenn’s Creek in 1812. While the creek provided vast quantities of water to run their grist mill it was the limestone spring system that fed the creek that was important to them. Not only did Pepper build a home he also built a stone spring house on the hillside below the home. The ruins of the springhouse exist today, still issuing crystal clear, cool spring water year-round. It was this water that provided the Pepper family with clean drinking water, primitive refrigeration, and more importantly the water used in their early distillery to craft Bourbon. Today the Woodford Reserve Distillery still uses that same spring water system to mash its grain recipes. Why change a good thing?