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Rum Maths – ABV

We’ve discussed Overproof rum before but after a recent chat with my Bajan brother-in-law, we felt compelled to take it one step further.

“Why do I see these bottles with 102% this and 151% that? How can you get 151% anything!?”

How indeed…well now for the magic! You can’t. Sorry Jerome but what you are in fact seeing on the labels of these wonderful spirits is a classic battle between old and new, imperial and metric, Proof and ABV.

So, let’s start at the end; what is ABV?

ABV is the acronym for Alcohol By Volume i.e. the number of millilitres of pure ethanol present in 100ml solution. The number of millilitres of pure ethanol is calculated by taking the mass of the ethanol and dividing it by its density (0.78924g/ml @ 20oC). ABV is now the worldwide standard for labelling the content of alcohol in a spirit.

Back in 16th century England, spirits were taxed at variable rates dependent on their alcohol content.  It was discovered that if you soaked gunpowder in a spirit and the gunpowder still burned, the spirit was considered above proof (yay) and therefore taxed at a higher rate (boo). For rum that level of alcohol was 57.15% ABV and this became known as 100 degrees Proof.

The gunpowder test was replaced in 1816 with the specific gravity test which lasted until the 1st January 1980. The test was to measure spirit with a gravity 12/13 of water (923kg/m3) and equivalent to 57.15% ABV.

It’s all about the math:

-> 57.15% ≈ 4/= 0.5714

-> 100o Proof = 57.15% ABV ≈ 4/7 ABV

-> 100% ABV = 100o Proof (7/4) = 175o Proof

e.g. 42.8% ABV = 42.8(7/4) = 42.8(1.75) = 75o Proof

Just to make matters more confusing, in the US (c.1848) the proof system established was based on % alcohol rather than specific gravity whereby 50% alcohol was the equivalent to 100o Proof.

So in summary:

UK: 57.15% ABV = 100o Proof (1.75ABV = Proof)

US: 50% ABV = 100o Proof (2ABV = Proof)

This would explain why Bacardi 151o Proof is by virtue of US standards 75.5% ABV.

Hopefully that explains a little bit more about the confusing world of Overproof rum. All that’s left now is to enjoy them!

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What Is Overproof Rum?

Many of us have heard of the term ‘Overproof’ when it comes to rum, the most famous examples being Bacardi 151 and Wray and Nephew Overproof.  But what does it actually mean and where does the term originate from?

The actual history of the term comes from many centuries ago when sailors in the British Navy were given rum. As rum became the norm for the sailors, they started to worry that the rations they were given were being watered down too much. The system they devised to check the quality of the rations was to mix a small portion of the ration with some of the gunpowder they had on board. This mixture was then lit to see if it would ignite. If it did ignite then the sailors knew their rum wasn’t watered down.

The sailors realised that this method would work, due to barrels of rum spilling onto the gunpowder in the past. When these spillages occurred with water, it would make the gunpowder useless. However, when the liquid spilt was rum, the mixture still ignited, much to the delight and relief of the sailors.

By using this method, the sailors had ‘proof’ the rum ration they were given wasn’t watered down. It is from this ‘proof’ we have evolved to the term ‘Overproof’ today which in basic terms means that the rum in question is flammable.

We have written a small piece on Overproof rum earlier which you can visit here. Let us know your favourite Overproof rum, and how you like to drink it!

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Angel’s Share

When rum is left to age in barrels after the distillation process, a portion evaporates. That portion is known as “Angel’s Share.” As it sounds, the portion given to the angels above.

Wray & Nephew recently introduced a new 50 year old Appleton Estate Rum to celebrate the 50th year anniversary of Jamaican Independence. In 1962 there were 24 barrels of the rum. By 2012 when being bottled only 14 barrels remained! That is an Angels share of almost 50%.

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How Is Rum Produced? (Part 1 – Sugar Cane)

In a previous article: Christopher Columbus and Sugar Cane, I mentioned how he transported sugar cane seedlings to the Caribbean. However, from that point there is still a long way to go before you get to the bottle of rum that is (hopefully) sitting in front of you.

The bulk of all sugar cane is still harvested by hand throughout the world. It is cut down by machete and then transported to machines which crush the sugar cane’s hard stalk. This extracts sugar cane juice. From here depending on the producer of rum we have three different options.

1)    If producing Rhum Agricole then the fresh juice is moved directly to the fermentation and distillation process.

2)    This juice can be cooked and concentrated into sugar syrup and then fermented and distilled from here.

3)    The fresh juice is then manipulated into molasses and crystallised sugar. The molasses are sold to distilleries and are fermented and distilled into the bulk of rums that are produced today. They also contain a noteworthy amount of minerals and other elements which contribute to the flavour of the final product.

From any of these stages, we end up with the raw materials for the next stage in production cycle, which is fermentation.

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How Is Rum Produced? (Part 2 – Fermentation)

Please visit Part 1 here if you haven’t already, about sugar cane.

Now we have the raw materials we can move onto the fermentation stage of production. It is from this point where huge amount of variation occur from distillery to distillery. The two extremes of the fermentation process vary from “natural fermentation” to laboratory conditions. Natural fermentation occurs in large open vats where the yeast in the environment ferments the sugars. It can be quite inefficient and unpredictable. Laboratory conditions include specific yeast cultures which are purchased by distilleries as well as precautions to minimise environmental affects.

The addition of this yeast (and to a lesser extent, water) is what converts the available sucrose into alcohol. The time is takes can last from just a few hours to a few weeks and also depends on the yeast that is added to the raw materials in this process. Once this has been completed and there is almost no sugar left, the distillation process can begin.

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How Is Rum Produced? (Part 3 – Distillation)

Please click here for Part 1 about sugar cane and Part 2 about the fermentation stage.

Now that we have fermented the raw materials, we can move on to distillation stage. The fermented liquid is placed in a still. During early stages of rum production, these were pot stills, but as technology has advanced these are now almost universally column stills. From here the still is heated to around 80 degrees C which is where alcohol boils and then evaporates. The steam created from this evaporation is then collected and re-condensed. When re-condensed, this liquid will be between 40-98% alcohol depending on the environmental factors in which it was created. This could be bottled and sold as rum if desired by the manufacturer. At this stage the rum will be colourless and clear and is quite raw.

It would be easy to say that this procedure seems quite basic and simple. However, there are a variety of different factors which go into this science of the distillation. The shape and size of the stills (which are hand made) all add to the final product. The stills could be very complex or remarkably simple. Also at this stage, some distillers may choose to remove certain chemical elements. We now have raw rum which could be bottled. But in most instances we now move onto our next stage in the production cycle which is aging.

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How Is Rum Produced? (Part 4 – Aging)

The first three stages of production can be found here: part 1, part 2 and part 3.

Now we have our rum, we move onto the aging process. This is done to help remove the harsh taste acquired from small amounts of hydrogen sulphide gas which is created during the fermentation process. Due to the high cost of barrels and the relative low cost of rum when it was first aged, rum has almost always and still till today, uses oak barrels which once were used to age whiskey or bourbon. These barrels not only add flavour to the rum but also colour. If the rum is aged in stainless steel tanks it will stay mostly clear. The minimum term rum will usually be aged for is one year.

Rum can be aged for decades if desired but depending on the process we get a loss of rum known as the angel or ‘duppy’ share. The higher the share, the less rum remains after the aging process. The highest angel share I have come across was quite recently where it was over 75% of the rum in the Velier Uitvlugt ULR 1997 (Review here). The final part is next and is the blending and bottling of the rum.

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How Is Rum Produced? (Final Part 5 – Blending & Bottling)

The earlier four parts can be found here: Part 1Part 2, Part 3 and Part 4.

Now we have aged the rum, the distilleries almost always decide to blend the rum with other batches some of which maybe aged for different periods of time. Spiced rums can also be infused with herbs, fruits and spices to produce flavoured rum. Also it maybe diluted with water to help bring the alcohol level down to 40-50%. Once the colour, taste, consistency and anything else the master blender wants to manipulate has been done, the final product is ready to be bottled and distributed. The entire process can be completed in weeks if you do not require your rum to be aged.

As you can see there are only between 3-5 steps for producing rum depending on how you want your final product. However, the endless possibilities in the variety of stages make rum an extremely unique product with endless flavour profiles!

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Rum Or Rhum – What’s The Difference?

If you have started to look for different rums when out or over the internet you may have started to see a change in certain spellings of rum. You may have noticed an ‘h’ being added to certain rums. This is not just a difference in spelling due to the region or place where the rum is made but there is actually a material difference in the manufacture of the rum from a very early stage of the process.

When the islands in the Caribbean were invaded and colonised they were done so by four major civilisations; English, Spanish, Dutch and French. All except the Dutch began distillation of rum on a large scale and as a result have different textures and tastes to each other. The English rums are deeper and full bodied rums e.g. Mount Gay from Barbados. The Spanish were crisper and lighter e.g. Brugal from the Dominican Republic. Both created rum using the molasses produced when making sugar from the sugar cane crop.

The French however not only used this process to make rum, but also decided to use rum made from sugar cane juice. They make a sugar solution from this called ‘vesou.’ Made in this way it is officially called Rhum Agricole, but usually shortened to Rhum. A major difference between molasses and cane juice is that molasses are very stable and can and are shipped all over the world. Cane juice however, is prone to degeneration and as a result is sourced locally so that it is fresh for the distilleries. It is also important to know that currently, Rhum makes up only about 3-5% of all rum production in the world.

As you can imagine using a different ingredient very early on in the production of a rhum would result in different flavours being found in Rhum than Rum. An example of a couple of well-known Rhum Agricole include Rhum JM and Clement both from Martinique. Next time you are at a bar, why not ask to try a Rhum and see how you find the difference between them