Every single day that I work the sales floor I meet a person who is flummoxed by the idea that single malt whisky is rarely one singular whisky. Or that many twelve year old Bourbons aren't the result of one continuous stream of brown whiskey coming off the still. Unless you're drinking single barrel hooch, you're never drinking just one whiskey -- you're drinking dozens, hundreds, or even thousands of whiskies that have been married together to create a specific flavor profile. Some products are composed of whiskies from the same distillery (as is the case with single malt whisky) and sometimes they can be a blend of different producers. They can be from the same type of cask, or a marriage of different ones. They can be all the same age, or a blend of different ages. There are so many aspects of the whisky-making process that can affect the ultimate flavor of a whisky that I feel it might be a good idea to list them here.
And it might help to compare them with wine because some spirits, like brandy and pisco, are distilled from wine, so that adds a lot of extra potential flavor factors.
Potential Flavor Factors of a Wine
Variety - This is an obvious one. What type of grape is being grown? Cabernet Sauvignon? Red or white? From what type of clone? Perhaps the vineyards are selection massale, meaning the the grapes are a propagation from a number of the vineyard's own most successful plants. Are the vines new or are they old vines? Older vines have deeper roots.
Terroir - When we're talking about making a wine, we have to begin by growing the fruit necessary to make a wine. That means grapes. The terroir factor in a wine's flavor depends entirely on where the grape was grown. What is the soil like? Is the vineyard on a hillside? How does that affect drainage? How does that affect sunlight? What is the weather like in this location? Pinot noir grapes that are grown in Oregon don't taste the same as pinot noir grapes grown in Burgundy. Cognac grapes grown in the Grand Champagne region aren't the same as the grapes grown in the Borderies. The flavor differences begin with terroir.
Viticulture - How does the farmer manage his vineyard? Does he use pesticides or are the vineyards organic? Or biodynamic? Does he harvest by hand or with a tractor? If the vineyard is machine harvested it can split the fruit prematurely and begin oxidation before the grapes are ready to be pressed. Does the farmer prune the leaves or create a canopy to increase photosynthesis? How are the vines spaced? What is the root stock? How large are the harvests? Concentrating flavor into fewer grapes can make a big difference. Is all the fruit being used from the farmer's own estate or is he sourcing fruit from another lcoation as well? Does he have control over that location as well? These are all very important questions that need to be addressed and understood.
Production Methods - How are the grapes being pressed once they've been harvested? Is one wine being made from the first pressing of juice and a second wine from the second pressing? Is chapitalization allowed (the adding of sugar to increase alcohol levels)? What about acidification? Are the stems being used during the wine's fermentation? What about the seeds? Maybe 50% stems, 50% destemmed? Maybe 25% stems/75% destemmed? Stems add tannin and earthy flavors to the wine, so leaving them in creates a different flavor. Destemming entirely helps to create a fruitier wine. Are the grapes cold-soaked, meaning the juice and skins been left longer to macerate and extract flavor without oxidation? How much sulphur is used before bottling?
Yeast and Fermentation - Is the yeast a commercial yeast meant to impart a specific flavor, or is the strain naturally cultured from the vineyard itself? What temperature is the fermentation allowed to reach? Hotter temperatures can extract more flavor, but also cook it right back out. How long is the fermentation allowed to last? Is it done in stainless steel or in wooden barrels? How long is the fermentation period? Oban, for example, is fermented for more than 80 hours to create a light and fruity style.
Maturation - Is the wine put into stainless steel? Used oak? New oak? A combination of both new and used oak? How long has the wine been in the bottle before you opened it? Is it a recent vintage or has it been aged longer? What type of cellar was the bottle aged it? What is the fill level like in the bottle? This will help tell you how much oxygen has permeated the wine.
Batching and Bottling - How many barrels are being used for the final wine? Perhaps a combination of some barrel aged selections and some stainless steel tanked wine? Is it from a single vineyard or is the wine a marriage of different wines? Were the grapes separated at the beginning and fermented to create different wines, then blended together at the end? Or were the grapes mixed from the beginning?
These are just a few of the things you need to think about when attempting to understand a wine's flavor. If you're talking Cognac or Armagnac, then you need to understand these concepts before even beginning with distillation.
Potential Flavor Factors of a Whiskey/Spirit
Base Material/Mashbill - What type of matter is being distilled? Corn? Rye? Barley? Maybe a combination of all three? Fruit? Wine? A percentage of both?
Terroir - I haven't found terroir to be a big factor concerning most whiskies, but some Bourbon distilleries are experimenting with GMO versus non-GMO corn. Bruichladdich and Kilchoman have local barley whiskies available (which are wildly different than their standard releases). Bryan Davis from the Lost Distillery here in California has also experimented with local barley and local peat. If the whisky is peated, where did the peat come from? With tequila, terroir makes a huge difference. Also with fruit brandies like Calvados.
Cooking, Malting and Creating Sugar - How was the barley malted? In a temperature-controlled vat or on the distillery floor? Was it raked? How often? Was it peated or not? With agave, was it steamed or baked in an oven? Or maybe roasted in a pit like mezcal?
Yeasts and Fermentation - What type of yeast was used? Four Roses is famous for using five different yeast strains with their two different mashbills -- each creating a very different flavor profile. Some tequila producers cultivate a natural yeast from their agave fields, much like wine producers do. How is the spirit fermented? In stainless steel or in wooden barrels? How long does the fermentation last? Oban, for example, uses an extra long fermentation time to help create a lighter, fruitier spirit.
Distillation - What type of still is being used? Pot still or column still? How much copper is involved? Is the distillation being done in batches? If using a pot still, at which point are the heads and tails separated from the heart? Are they dumped back in to be redistilled? How high is the column still? How many rectification plates are in the column? Is only the fermented liquid being distilled or is the base material added into the still as well?
Maturation - What type of barrel was used to mature the whiskey? Brand new charred oak like Bourbon? Or was it a used barrel like with single malt? If the barrel is being reused, what was in the barrel previously? Bourbon? Sherry? Port? Wine? How many times has the barrel been reused? The more often it's been used, the less flavor it can inflect into the whiskey. How long was it aged? In what type of warehouse? Is it hot or cold where the warehouse is located? Is the warehouse inland or by the sea?
Batching and Bottling - This is where the number of permutations can really boggle your mind. Is the whiskey you're drinking a single barrel whiskey from one cask only? If it's a small batch whiskey, how many barrels were used? Which types of barrels? All Bourbon? A mixture of Bourbon and Sherry? Some old barrels, some young barrels? If the whiskey says "12 years old" is all the whiskey 12 years old, or just the youngest ones? Producers only have to state the age of the youngest whiskey in the marriage. Are all the whiskies from the same distillery? What proof is the whiskey bottled at? Was some water added? No water? Is the marriage a blend of one type of whiskey, or is it both grain whisky and single malt whisky like Johnnie Walker Blended Whisky? Is it a straight Bourbon whiskey or a blend of both rye and Bourbon like High West's Bouyre? When you buy a whiskey more than once it's rarely the same as it was previously. While producers are very good at matching flavor profiles, batches can be wildly different from one another despite the fact that you're buying the exact same product as before.
There are probably some important things I'm forgetting, but this should cover most of the basics. I'm doing this off the top of my head right now. Nevertheless, the point is that many, many, many things affect the ultimate flavor of a wine or whiskey and they need to be understood in order to truly appreciate what's in your glass. These are the things that make one product different from another. These are the things that separate great producers from mediocre producers. And we haven't even talked about sterilization!