Aging of Scotch takes place in an oak cask, which is charred inside before being filled. Over the years, the whisky seeps in and out of the charcoal. This filters it, mellowing it, and gives it the caramel color (charred wood, like charred sugar, produces caramel, both being of similar chemical composition.)
Some would try to speed the process. They add caramel coloring to the blend, to make it look like it has spent the time aging.
Some distilleries, like The Macallan, make a big deal of using oak casks from Jirez, Spain that were used to hold Sherry wine. They char them and use them as normal. It adds a bit of Sherry wine taste to the Scotch. Whether or not this is superior, I leave to your discretion. I can take it or leave it. Others use barrels formerly used for aging American Bourbon Whiskey (Laphroaig), others insist on new oak barrels (Glenmorangie). Many use some of each kind of barrel and marry them before bottling (Glenfiddich).
Finally, most Single Malts are dilluted to bottling strength (usually 86 US proof/43% alcohol) with spring water. Cadenhead and a few others bottles "cask strength" single malts, at the proof level of the barrel, often around 105 proof (52.5% alcohol). Also, so-called "Single single Malts" are bottled directly from a selected cask, instead of from the combination of all the casks from that distillery for that year.
Speyside Malts
Geographically grouped in the Highlands, Speyside Malts vary from the delicacy
of higher altitude Highland Malts to some of the rich flavours of the
Islay Malts. The Glenlivet is a Speyside-located Highland Malt. I always get
this confused, because I think of Islay when I hear Spey. Spey is a river that
runs through the Highlands, but most of the distilleries are by the last few
miles of the river in a valley (the low Highlands? I don't know!)
Single Malts are made from Malted Barley only. Grain whiskys are made from unmalted barley, wheat and other grains. Blends include both malt whisky, and grain whisky.
Your average Scotch is a blend, like Chivas Regal. By blending different distillations, weaknesses can be hidden or compensated for, and strengths can be compounded. If the Masters are good at what they do, they can produce consistent blends year after year.
Single Malts, on the other hand, are much more of a challenge for the distiller. After a few years, the whiskey is sampled to see if it is good enough to be bottled as a Single Malt under the distillery's name. If not, it goes to a larger firm that blends it with other distillations.
A marrying of Malt whiskies from different distilleries, containing no grain alcohol.
Hey, did you know about the etemology of one of these words?
After this erudite elucidation I'll just wonder on home.
Or, I'll have another wee dram of scotch.