Dimensions of Rum

Base Ingredients

Rum is made by distilling sugar cane derivatives—principally molasses and byproducts from molasses production
Rhum Agricole and Cachaça are made from sugar cane juice. Since cane juice retains more of the flavor of the sugar cane, regional nuances are easier to taste than in molasses-based spirits.

Pot still, favored in Jamaica and used by most small-scale distilleries. Pot still rum has a complex and robust flavor.
Column still, used by any large-scale rum distillery e.g. Bacardi, Cruzan, Brugal, etc. In general, the flavor from column still rum is cleaner and less nuanced than pot still rum.

With few exceptions, rum is blended from multiple sources. Combining spirits from different locales, produced by different methods, and aged in different amounts is more of an art than a science. As such, the master distiller plays an outsized role in shaping the experience of the resulting spirit.
During the blending process, some rums are sweetened to change their flavor profile. It is hard to find reliable information about which producers sweeten with rums. Plantation, for example, is a distiller that frequently sweetens their rums.

Like most spirits, rum is aged in barrels (or stainless steel basins lined with strips of wood). Rum is traditionally aged in oak casks.
Most rum is aged near where it is distilled: in the tropics. The warm, humid environment catalyzes the aging process. Because of this, an 8-year rum from Puerto Rico will taste closer to a 12-year Scotch than an 8-year Scotch. Scotch wiskey is aged in Scotland. Scotland is a long way from the tropics.

Locale influences the distilling practices, both in term of distillation method and blending style.
There is some variation in the flavor of the spirit depending on regional differences e.g. rainfall, soil varieties etc. Regional variations in flavor are more pronounced in Rhum Agricole.

Rum has always been spirit with a high alcohol content. One of the early names for rum was “kill-devil” to impart that it was “a hot, hellish, and terrible liquor”.
The British developed the proof system for measuring alcohol content in rum to determine the appropriate tax rate. Gunpowder does not burn if soaked in rum that is less than 57.15% ABV (roughly 4/7). Thus, if the rum was strong enough for the doused gunpowder to light it was “proof” of the rum’s sufficient strength. (Unlike the British system, which measured specific gravity, the American proof system measures the percentage of alcohol so the proof numbers between the two standards differ.)
Rums are typically 80 proof but there are also “overproof” rums e.g. Journeyman Road’s End Rum (90 proof), Plantation OFTD (138 proof), and Bacardi 151 (151 proof).