It has become customary in Scotland for distilleries to sell barrels of whisky to blenders and independent bottlers as a means of making additional income. In fact, some distilleries exist solely to serve independent bottlers, and do not market any brands themselves.
Distilleries also pass on barrels of whisky to ensure consistency. When blending whisky, they ensure consistency by using barrels with similar flavours. If a particular flavour is notably different, it may be deemed uncharacteristic of the distillery and as such cannot be used in "official" product bottlings. Whiskies bottled by independent bottlers may or may not be labelled with the distillery of origin, but tend not to use the distillery's trademarks such as logos, fonts and images as they may not have the authorization to do so.
In general, the fact that a whisky was produced by an independent bottler does not, by itself, provide any indication of quality. Independently bottled whisky ranges from "bottom shelf" products of low price and quality to the finest classes of whiskies. However, an independent bottler can sometimes provide more niche-style products due to the nature of their business model.
Independently bottled whisky is sometimes bottled at cask strength, which means it is not diluted from the strength that comes out of the barrel. This often results in a more full-flavoured whisky, because lowering the strength by dilution also dilutes the flavour. Independent Bottlers may also not chill filter the whisky, a process which involves removing fatty acids, proteins and esters to give the whisky a clearer appearance. Chill filtering can affect flavour, however, because these compounds account for a lot of the taste (the esters, for example, have a fruit-like aroma). One further measure often not taken when independently bottling whisky is the addition of spirit caramel for colouring.
Due to the long history and marketing campaigns undergone by some distilleries, their brands may be associated with a great deal of prestige. As such, proprietary bottlings can sometimes command a higher price than an independently bottled whisky from the same distillery. Because of this, independently bottled whisky is often much cheaper, which can enable connoisseurs and whisky drinkers to try "rarer", older whisky without paying quite so much. However, as distilleries often strive for consistency, and are careful not to tarnish their reputations, their branded bottlings can sometimes be more reliable.