A blended whisky is made when different kinds of whisky are mixed together, typically mixing a 100% malt whisky, with another derivative, which will often be created using different grains and other ingredients to the purer malt. It is not unusual to have anywhere from 15 to 40 different single malt whiskies and grain whiskies in a blended whisky.

Because of blending, it is possible to take several inferior tasting whiskies and come up with a unique whisky blend that is better tasting than any of the individual whisky types it contains. Distilleries can take years acquiring the art of a blended whisky which contains malt and grain whiskies that complement each other and have a unique and palatable taste.

Blending is an art which may involve experimentation to achieve the best flavouring. Blending in no way dilutes the whisky, in fact additional flavour can be achieved through the aging time and type of wood used for the aging cask. It's important to note that in Scotland, whisky must be aged at least 3 years before it can be classified as whisky. It's not unusual for some whisky to be aged for more than 20 years, which adds to the flavour, much the same principle as wine.

A single malt whisky is considered the best by purist whisky drinkers and a blend is considered inferior, since blended whisky uses other ingredients which act as fillers for flavouring. Grain alcohol is an ingredient on any bottles that are “blended whisky”, as opposed to “blended Malt whisky” or vatted malt, which means that it is a blend of only malt whisky, in different formulations. Typically, blends may have 65 to 85% grain whisky and 15 to 35% malt whisky.

It's not unusual to have blended whisky that has a sweet taste of honey, a smoked flavour, a fruity flavour or something else entirely. Many whisky drinkers actually prefer blended whisky because they are sometimes smoother and have better flavours. Blenders also may mix caramel in for colour uniformity.

In blending, the grain whiskies are neutral and the single malt whiskies are what might bring the flavour. Certain malt whisky, such as Island or Islay malts have a spicy rich flavour, while Speyside malts may have a smoky, fruit, apple or sherry character.

Once a successful blend of whisky has been achieved, the blender has to determine demand in the future and has to decide when the different single malt whiskies will be ready to use in a blend versus grain whiskies. In other words, flavour enhancement can come in varying ages, where some might peak at 5 years and others might take 10 or 12 years.

Once they have reached maturity, they will be mixed in a blending vat and returned to the aging cask for the flavours to mingle for months, in order to improve flavor; although there are some distilleries that bring them together in the bottling stage. The process of combining malt whisky with other malt or grain whisky is known as vatting, which is why you may hear blended whisky also referred to as vatted whisky.

Blended whisky is a certain recipe of different whiskies that have a distinct taste, and most whisky drinkers tend to stick with certain blends, once they have found the one they prefer most.