After writing about spirits for a good many years, we thought we had a grasp of the most important aspects of bourbon and other fine American whiskeys. We were wrong. It wasn't until we started our in-depth research about American whiskeys, toured the distilleries, scoured the archives, and interviewed the most knowledgeable whiskey folk in the industry, that we started to understand all of the nuances that surround the various terms and phrases that are commonly thrown into bar conversations - and seldom understood. Here, then, we bring you the fruits of our oh-so-tiring, but very enjoyable investigation of the American whiskey industry.

Alaskan Bourbon
    No, there's no such thing as bourbon from Alaska - but there could be. Legally, due to a congressional proclamation issued in 1964, bourbon must be made in the United States. But it doesn't have to be made in Bourbon County, Kentucky (where there are no distilleries at present), or even in the state of Kentucky.

    At the time of writing, all but two bourbons are made and aged in Kentucky. One is a brand made for "export only" in Illinois; the other is a bottling named Virginia Gentleman. The bottles of Virginia Gentleman currently on the shelves were distilled and aged in Virginia, although the company now purchases once-distilled whiskey from a Kentucky provider, puts it through its second distillation in Virginia, and ages the whiskey in their own warehouse in Virginia.

    Although bourbon can be made anywhere in the U.S., it must be made with a predominance of corn, and whereas the government stipulates only that a minimum of 51% corn be used, most distillers use upwards of 70 % of this indigenous American grain. The other grains used to make bourbon (known as "small grains"), though not stipulated by law, are malted barley and either rye or wheat.

Straight Whiskey
    There are three main types of straight American whiskey - bourbon, rye, and Tennessee - and all three must be made in accordance with certain criteria laid down by law. (Corn whiskey, which can also be designated as a straight whiskey, differs from the regulations below inasmuch as it must be aged in either used, charred oak barrels, or new, uncharred oak barrels.) Some of the regulations are, of course, rather technical, but here are the main points that differentiate straight whiskeys from their blended cousins. (We've added some explanations of what these rules mean to the consumer.)

Straight bourbon, rye, and Tennessee whiskey must be:
1. Distilled out at less then 160 proof (80 percent alcohol by volume [abv]). The fact is, most American straight whiskeys run off the still at between 62.5 and 70 percent abv, and by keeping the proof low, the distillers ensure that more flavor stays in the whiskey. In comparison, vodka usually comes off the still at almost 95 percent abv.

2. Aged for a minimum of two years in new charred oak casks. However, if the whiskey is matured for less than four years, its age must appear on the label. Therefore, most of the straight whiskey that appears on liquor store shelves is bound to be at least four years old. Many people think that whiskey must be aged in American white oak barrels, and indeed, all American whiskeys that we know of do spend their adolescence in that particular variety of oak since the configuration of the grains make it ideal for holding liquid. But this is merely the choice of the distillers, no specific type of oak is laid down by law.

3. No coloring or flavoring may be added to straight whiskey. When whiskey runs off the still it is clear - just like vodka - and it tastes similar to an eau-de-vie. But as the whiskey ages, certain impurities, known as congeners, react with the wood and develop into the "flavor particles" in the spirit. The color of straight whiskey is mostly a result of the spirit expanding into the charred wood during the warmer months and gaining color from the "red layer" in the barrel. So what's the red layer?

    When the barrels are formed, the staves are heated to help them bend, and the heat caramelizes some of the wood sugars and tannins within each stave. This toasting stage of coopering forms the red layer, which not only helps give color to the whiskey, but also imparts some extra flavors. After the barrels are formed, their interiors are then charred over open flame creating a layer of charcoal over the red layer. When the whiskey is in the aging houses, it filters through that charcoal as it expands and contracts with seasonal temperature changes, or in certain cases, by artificially raising and lowering the temperature in the warehouse. Both the red layer and the charred interior add flavors to the whiskey.

    Those, then, are the main points that concern us when dealing with straight American whiskey. Blended whiskey, on the other hand, is flavorful straight whiskey that has been blended with flavorless neutral grain whiskey. Further, blended whiskeys can have other flavorings and/or colorings added. Don't discount blended whiskeys out of hand, many of the top-name brands are sterling examples of the blender's craft, and should be enjoyed in their own right.

Bottled-in-Bond
    Just about 100 years ago much of the whiskey being sold as "straight whiskey" was anything but. So much of it was adulterated in the name of greed--flavored and colored with iodine and tobacco - that a bunch of reputable whiskey distillers, led by Colonel Edmund Haynes Taylor, Jr. (creator of Old Taylor bourbon), joined with then Secretary of the Treasury John G. Carlisle to fight for the Bottled-in-Bond Act of 1897.

    The Bottled-in-Bond Act stated that distillers could store their barrels of straight whiskey in governmentally supervised warehouses for a period of at least four years. After the aging period the government would certify that this same straight whiskey would be bottled at 50% abv and vouch for the aging period. As a result of governmental guarantees, bottled-in-bond whiskeys became very popular spirits in the early twentieth century. To this day, some consumers tend to look on the term as an endorsement of quality, although any straight whiskey bottled at 100 proof that doesn't bear an age statement (denoting a minimum of four years in the wood) is of a similar caliber. The only difference that might occur is that bottled-in-bond whiskey must be the product of one distillation season, whereas bottles without an age statement may be a product of mingling straight whiskeys of differing ages to achieve consistency. But this can be a plus - sometimes 5-, 6-, or even 8-year-old whiskeys are mingled with four-year-olds in order to arrive at the product's flavor profile. The age on any bottle of American whiskey denotes the age of the youngest whiskey in the bottle; older whiskeys can be and often are added.

Sour Mash
    Oh, the barside arguments we have witnessed about this term, and very few people get it right. Here's the scoop: Sometime after 1823 a Scottish distiller by the name of Dr. James Crow (creator of Old Crow bourbon) perfected a method of making whiskey that involved draining the liquid from the mash of fermented, cooked grains that were leftover from the primary distillation. He then added a portion of this liquid to the mash of cooked grains and yeast that would be used for his next batch. (Crow also insisted on aging his whiskey in charred oak barrels - we think of him as the father of bourbon as we know it.) We look on sour mash, a.k.a. backset, as whiskey DNA - it not only brings the character of each batch of old whiskey into the new mash, it is also used to control the acidity of the mash and create an environment perfect for the new yeast.

    Whether or not the words "sour mash" appear on the label, every straight American whiskey currently being produced is a sour-mash whiskey. Most often, during the drinker's debates we have heard, people look at a bottle of Jack Daniel's or George Dickel, see the words "sour mash," and claim that that phrase is the reason that these whiskeys don't bear the name bourbon, but it just ain't so - these are Tennessee whiskeys. And they, along with some bourbon companies, merely decided to put "sour mash" on their labels.

Tennessee Whiskey
    If George Dickel or Jack Daniel were alive today, they would be proud that today's versions of their whiskeys aren't called bourbon - Tennessee whiskeys are very special. Way back in the 1820s there lived in Lincoln County, Tennessee, a distiller by the name of Alfred Eaton, and he is said to be the man who first discovered that when he filtered his whiskey through giant vats of sugar-maple charcoal, it became a much smoother product. Bear in mind that back in those days, whiskey wasn't usually aged, so any process that took the rough edges off new whiskey was very desirable.

    Eaton's procedure is now known as the Lincoln County Process, or charcoal mellowing. We have tasted Tennessee whiskey straight off the still, and again after the mellowing process and can vouch for the fact that it is this leaching over sugar-maple charcoal that gives the Tennessee whiskey the wonderful "sooty sweetness" that is not present in bourbons.

    But don't be confused. Though your bottle of bourbon may bear the words "charcoal filtered," the process is different from the Lincoln County Process. Most bourbons - in fact Booker's bourbon is the only exception - are filtered after aging and before bottling with activated charcoal. Some are filtered at room temperature, others are chilled and then filtered, but the process is quick and meant solely to remove certain impurities that affect the visual appeal of the whiskey. No flavor is imparted by activated charcoal. Why do it? Because when unfiltered whiskey gets too cold, it can develop a "chill haze" or cloudiness. There's nothing wrong with cloudy whiskey, in fact, it is generally more flavorful than the filtered variety, but the public at large doesn't know that. They think the whiskey is spoiled in some way and don't want to buy it; therefore, distillers generally filter their bourbon before bottling it. Tennessee whiskey goes through the same quick filtration process after aging.

    "Wait a minute," you say, "I thought that straight whiskeys couldn't have any flavors added to them, and now you are telling us that the Lincoln County Process adds flavors." Think of it as a loophole that we should celebrate. Just like the German beer, Rauchenfels Steinbier, that has red-hot stones dropped into it to caramelize the sugars and therefore change the flavor without straying from the German purity law that states that nothing but water, hops, yeast, and malt be used to make beer, Tennessee whiskey is legally filtered through a substance that just happens to add its own nuances to the end product.

Straight Rye Whiskey
    When Prohibition was repealed in December, 1933, many whiskey drinkers were looking for the pure rye whiskey that had been so popular before the Noble Experiment. However, since distillation had been, for the most part, banned for almost 14 years, there wasn't enough aged product on hand at the American distilleries. Enter the Canadian whisky distillers. Pioneers such as Joseph E. Seagram and Hiram Walker had plenty of blended Canadian whisky on hand, and it was common at the time for the Canadians to use a fair amount of rye in the their production (these days, little or no rye is used). As time went by, Canadian whisky became know as rye whiskey, and to a great extent, Americans lost their taste for straight rye whiskey.

    As we stated, bourbon must be made from a mash that contains a minimum of 51 percent corn (although most contain over 70 percent), and same applies to the rye content in a straight rye whiskey - usually made with over 65 percent rye. If you have never tasted straight rye whiskey, rush to the liquor store and demand that they order a bottle for you. Ryes are delicate, yet peppery, and far different from either blended whiskies or their cousin bourbon. Indeed, rye whiskeys were the favored dram of Americans in the mid-1700s, almost 50 years before Kentucky bourbon hit the scene.

Small Batch Bourbon
    This term has been the source of much confusion since most bourbon lovers believe that "small batch" denotes whiskey that has been distilled in small quantities. But that isn't true. In fact, small-batch whiskeys are the result of another side of the distiller's craft altogether. The term was introduced in the late 1980s by the Jim Beam Brands Company, and according to them, the term applies to "rare and exceptional Bourbons married from a cross section of barrels in the rack house." Fact is that different sections of a bourbon warehouse produce different whiskeys - most of the buildings are between seven and 12 stories tall, and since the temperatures differ on each level (progressively hotter toward the top), the whiskeys mature at different rates. Distillers of small-batch whiskeys select barrels that have aged into particular styles and mingle them together to achieve consistency. Since not many barrels mature into a style consistent with the quality that these distillers seek, they are, indeed, "rare and exceptional."

    Having said that, however, we must point out that there are many rare and exceptional bourbons out there that aren't designated as "small batch" bottlings, simply because the producers shy away from a phrase that might confuse their products with those from another company.

Single Barrel Bourbon
    These whiskeys are, like their small-batch cousins, selected from prime areas of the warehouse. However, in the case of single-barrel bourbons, the distiller doesn't have the luxury of marrying one barrel with another to achieve a particular result. Each bottle of a single barrel bourbon may differ slightly from the last if it came from a different barrel (check the label, the barrel number should be noted), but each master distiller selects whiskeys that have matured into a specific "flavor profile," and are, therefore, very similar to one another.

Vintage Bourbons
    At the time of writing, Evan William's Vintage Bourbon is the only Vintage-dated bottling on the market. It is also a "single barrel" bourbon. The only real difference here is that the distiller has chosen to note the date of distillation on the label, signifying that this is a special selection that is worthy of note. We have only one small quibble with the Evan William's vintage bottling: Each bottle bears the date on which it was distilled, but not the date on which it was bottled - how are we supposed to know the age of the whiskey? (For the record, this whiskey is a very respectable eight years old, and a darned fine bourbon to boot.)

In Conclusion
    We hope to have cleared up most of the barside arguments about bourbon, rye, and Tennessee whiskey here, but no doubt the guy at the end of the bar wil still insist that bourbon must be made in Bourbon County, and that Tennessee whiskey is the only real sour mash on the market. You, however, can now rest easy when you ask him if he would like to wager a shot of whiskey on the subject, and have the bartender ready to pour you a free dram.

Gary Regan and his wife, Mardee Haidin Regan, have written several books, including "The Book of Bourbon and Other Fine American Whiskeys" and "The Bourbon Companion - A Connoisseur's Guide".