Sugars in Rum that Get There from the Aging Barrels

Former Bourbon Barrels Filled With Rum

     There are small amounts of sugar in all rum. Most aged rums will have some sugars dissolved from the oak cask and often some from optional Caramel coloring.  Total amount of sugars are quite low, usually well below 1 gram/liter, but in certain cases it is quite possible to reach a few more grams per liter.   The sweet aromas of rum matured in used bourbon or new oak casks mostly come from sweet aromatic vanillin and fruity esters, not from the sugars.  However, sugars can have a significant role in the case of casks previously used for sweet wine or a sweetened spirit.

Barrels Repaired in Cooperage

     Another source of sugars in rum is wood. Oak is composed of three main macromolecules; cellulose, Hemicellulose and glucose.   Cellulose breaks down very slowly in alcohol-water solution extracting very small amounts of glucose to the rum.  Most sugars extracted from the cask come from hemicellulose, most of which are 5 carbon sugars.  

Large Aging Warehouse in Trinidad      Probably the most important factor considering the amount of sugars in rum is the previous content of the cask. The most common type of cask is an ex-bourbon cask.  These will impart minimal amounts of sugars, often well under 50 mg/l/year and overall well below 1 gram/liter even during a long maturation.  The charred American oak cask used for bourbon is quite low on sugars to start with and the bourbon will extract a major part of the available sugars.

Rum can, and often does, contain added sugar or other sweeteners.  Most sweetened rums are sugared at the bottling phase, but sometimes sugar or molasses, cane juice, fruit etc has been added already into the cask and some of that sugar is bound to get into a cask that was used previously for rum.  Up to 40 grams/liter sugar contents have been reported in rum and up to 100 g/l in spiced and flavored  rums, but when the sugar added directly to cask the finished product is usually in the range of 5-20 grams/liter.  Oloroso Casks Filled with Rum    Significant amounts of sugar can be extracted from a sweet wine cask.   Sherry is by far the most used ex-wine cask in the rum industry.   Most sherries, such as fino, manzanilla, amontillado, palo cortado and most olorosos, are dry wines in the range of 0-5 grams/liter of sugars and add very little sugar to the cask.  The sweetness perceived in the olorosos often comes from high amounts of glycerol, not as much from sugars.  A notable exception is Pedro Ximenez wine, which nowadays is produced almost exclusively in Montilla-Moriles, a Spanish Denominación de Origen.  It is a sweet wine produced from late harvested dried PX grapes and it typically contains by law over 212 grams/liter of sugars. It is quite sweet even compared to other sweet wines, such as port that has 100-150 grams/liter, Sauternes at 100-200 grams/liter or a Tokaji that has 60-500 grams/liter.     What does this all mean in the finished product?   It basically that sweetness in you rum may not be coming from added sugars.  By aging in final finishing in casks that were used for finishing sweet spirits and wines can impart their sweetness to the rum as it is being aged.  This is a process that takes time in the barrel, but it does give you not only a sweetness, but picks up some of the previous fill in  the barrel.  I love rums that have been finished in wine casks, they add a really nice finish to the final product. There is a lot more information you can read on the subject at http://whiskyscience.blogspot.dk/2016/12/sugars-in-whisky.html?m=1