Traditional molasses rum

Molasses rum is the traditional way of making rum. It represents more than 90% of the world's production. In the past, each distillery depended on a sugar factory, which is why it is also called "sugar mill rum" or "industrial rum".

In the early days of cane sugar and rum, the skimmings from the cooking of pure cane juice or the cane juice itself were distilled. However, the knowledge and methods of the time did not yet allow for the proper treatment of these fragile materials. It became apparent that molasses, which was stable and easy to preserve, was much more reliable.

This by-product of sugar production was previously used to feed cattle and slaves. It became a very interesting outlet for the plantation owners. They were able to use this effluent to make rum.

Molasses production

When the sugar cane arrives at the factory, it passes through a shredder. It is then pressed in large horizontal rollers. This operation is repeated in order to obtain all the juice, often by soaking the cane with water to facilitate its extraction. This cane juice is then heated, in order to get rid of its water, and thus concentrate it in sugar.

Cane juice is primarily composed of sucrose, glucose and fructose. During the cooking process, a few sugar crystals are sown on top of which the crystallised sucrose clumps together to form larger crystals. Next to the crystals a black, viscous liquid is formed, which is called molasses. At this stage, the whole thing can be centrifuged and a rich sugar can be recovered, still full of molasses. This is the complete sugar, also called muscovado.

From cane honey to Blackstrap molasses

The molasses obtained after this first stage is called cane honey in Latin American countries (e.g. Diplomatico in Venezuela). It is known as "Grade A molasses" in English-speaking countries. It is a molasses very rich in sugars, similar to battery syrup.

The process can then be repeated, and the cane juice heated and centrifuged again. The result is a low-refined Demerara brown sugar and a B-grade molasses. When the juice is evaporated again, a highly refined sugar is obtained. The by-products of this process are the "blackstrap molasses", which is depleted of its crystallizable sugar. Although no more crystallised sugar can be obtained from this molasses, it is not without fermentable sugar (which is of interest to us in the manufacture of rum).

The choice of molasses

Blackstrap molasses is the cheapest for distillers. But it has a lower sugar concentration than first-cooking molasses, more impurities, and carries less of the original cane flavour. Therefore, larger quantities are needed to achieve the same yield as with cane honey. It is said that the less efficient the sugar factory, the better the molasses, and vice versa. The choice is then up to the distilleries. They have to find a balance between flavour, production costs and yield.

Distilleries with their own sugar factory are nowadays more and more rare. They therefore buy their molasses from all over the world, trying to respect certain specificities which allow them a stable and continuous production. To do this, they often use brokers who buy from the major molasses producers in South America or Asia.

Some distilleries, such as Privateer in the USA, ensure a regular supply by working with only one sugar factory in Guatemala.

Molasses and rum

To make rum, the viscous liquid that is molasses must be diluted before it is fermented and then distilled. This is usually done with water, the quality of which is extremely important in this case. But it can also be done with vinasse, the residue of previous distillations, in the Grand Arôme or High Ester method.

This is followed by inoculation with yeast. They are also very important, as they strongly influence the final aromatic profile. This yeast addition can also be natural and spontaneous. This is once again the case for grand aroma rums or certain Jamaican rums, for example.

To learn more about this topic, visit our blog post: The crucial fermentation stage in rum production.

Types of molasses rums

Light rums have less than 225 grams of aromatics per hectolitre of pure alcohol, and often much less (20-90 g/hlap).

Traditional rums have a quantity of aromatic congeners higher than 225 g/hlap.

Highly aromatic rum contains aromatic compounds (non-alcoholic) in quantities of more than 500 g/halp.

In terms of styles, molasses rums are best represented in the English (rum) and Spanish (ron) traditions. Read less