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Good Vibrations – How Coriolis Measurement Techniques Keep the Scotch in Whisky

​When it comes to the production of Scotch whisky, accurate measurement is everything. Strict regulations around the taxation of alcoholic spirits, plus the added need to ensure a minimum alcohol content to qualify as an official Scotch, make it essential for whisky producers to make sure that the levels of alcohol in their beverage are carefully measured.

​Today’s whisky producers must adhere to strict regulations that were implemented over 100 years ago.  In 1916, the Chancellor of the Exchequer, teetotaller David Lloyd George, was charged to raise money for the war effort and attempt to curb alcohol consumption.  

After much protestation from the whisky industry, a compromise was met which agreed that a standardised strength of 42.9 percent alcohol by volume (ABV) would be implemented.  Later in 1917, when Lloyd George became Prime Minister, a legal minimum alcohol content was agreed and was set at 40 percent ABV. This limit still stands today and is required for any spirit to be legally considered Scotch whisky. 

Requirements for the measurement of the alcoholic contents of spirits, including Scotch whisky, are set out in the HMRC’s Excise Notice 39: spirits production in the UK. The Notice sets out various procedures that need to be followed, including the requirement for producers to submit quarterly production returns stipulating both the quantity of ingredients used and the amount of spirits produced. These returns must be accurate, with any deviations or errors potentially attracting financial penalties.

Another key requirement is the need to measure the alcoholic strength of the whisky itself. Regulation 18 of the Spirits Regulations 1991 calls for precise and accurate measurement of the density of the whisky during distillation, with measurements being taken at a temperature of exactly 20°C. 

Coriolis measurement scotch whisky

Further requirements are imposed by the Scotch Whisky Regulations 2009. Under these regulations, for a spirit to be called Scotch whisky it must be matured in oak casks not exceeding 700 litres in capacity for a period of no less than three years. These casks, which cannot leave Scotland, must be situated in an excise warehouse or other permitted place, with the whisky then being transferred at the end of the maturation process.

During the maturation period, which can range up to 15 years or more depending on the product, the whisky must be kept at less than 94.8 percent ABV, which maintains alcohol content but also ensures the whisky has the correct taste and aroma derived from its raw materials. 

Requirements are equally as strict when it comes to the transfer of the whisky from one place to another. Excise Notice 197: receipt into and removal from an excise warehouse of excise goods, for example, makes excise duty on spirits chargeable as soon as they are taken out of warehouse storage. In the same way as during production, careful measurement of the quantities of whisky being transferred is necessary to minimise the risk of any errors that could increase the amount of duty levied.

Making the difference between Scotch and not

In basic terms, the alcohol by volume (ABV) level of whisky is defined as the number of millilitres (ml) of pure alcohol present in 100ml of the whisky at 20°C. To derive this figure, the mass of the alcohol must be divided by its density at 20°C.

The strict requirements for what can officially be called a Scotch whisky require ABV levels to be closely measured and controlled. If whisky is distilled at a level above 94.8 percent, for example, it will be considered by law as neutral, as Scotch must be produced containing the right taste and aroma.  Equally, after distillation and during the casking process, the alcohol concentration needs to be at a strength of 63.5 percent ABV to ensure the taste and quality of the whisky is of the highest standard.

The ability to accurately measure the ABV of whisky during the distillation process is particularly important when it comes to estimating the Excise duties on the whisky.  As this is based on the litres of alcohol contained in the final product, it is important to ensure that the measurement is correct, especially as any discrepancies can result in the imposition of added duty.

Capable of measuring mass and volume flows as well as density, Coriolis flowmeters provide the ideal solution for both whisky distillation and custody transfer.

Coriolis flowmeters work by rotationally oscillating the fluid, which produces equivalent coriolis forces. Tube designs are U-shaped, S-shaped, or straight.

In U-shape or S-shape tube designs, the fluid moves away from and back towards the axis of oscillation, resulting in a changing angular momentum of the fluid. As the tube oscillates up, the fluid mass flowing into the tube will resist its increasing angular momentum and push down against the tube.

As the fluid moves back toward the axis, it resists its decreasing angular momentum, pushing up on the tube. These opposing forces depend on the fluid’s mass. They deform the tube with a twisting action.

The two opposing forces twist the tube first one way, then the other, with each oscillation cycle. Waveform outputs from the pickup sensors are sine waves, reflecting the oscillation frequency. Measuring the magnitude of this deformation enables the mass flowrate to be derived.

With zero flowrate, the two sine waves from the pick-ups are in phase with each other as the fluid’s angular momentum is constant and no twist occurs. As flow increases, the phase difference between the two sine waves also increases.

This phase difference produces the measure of the mass flow rate through the coriolis flowmeter. The greater the mass flow, the greater the twist, and the greater the measured phase difference.

DN25 integral sensor / Coriolis Measurement Techniques

Straight tube designs operate in a similar manner. The vibrating tube is fixed at its ends, creating two rotating reference frames. The rotations at the inlet and outlet sides are in opposite directions, creating opposing Coriolis forces that distort the tube.

In most designs, the tube oscillates at its resonant frequency, which depends on the meter tube geometry, the characteristics of the flowmeter materials, and the mass of the fluid in the meter tube. Using these properties, it is possible to calculate the fluid density within the tube, making coriolis flowmeters ideal for measuring the alcohol density of the whisky.

The flowmeter also includes a thermal sensor to account for dimensional and elasticity changes of the tube with fluid temperature, which eliminates any potential errors in the mass flow measurement.

Furthermore, because the coriolis metering principle is independent of the fluid's density, temperature, viscosity, pressure, and conductivity, it is independent of Reynolds number as well as upstream and downstream flow velocity profiles. Consequently, coriolis flowmeters require no straight runs of piping on either side, reducing both installation space and cost.

A key benefit of coriolis meters is their accuracy. Accuracies of ABB’s own CoriolisMaster flowmeter models, for example, range from 0.1 to 0.4 percent of reading for liquids and 0.5 to 1 percent of reading for gases.

Such accuracy means whisky distillers can ensure they are providing HMRC with the most accurate measurements for both the quantity and density of whisky produced, which can then be used to calculate the appropriate level of tax.

The requirement to turn mass measurements into volume flow to meet HMRC requirements can also be satisfied by coriolis flowmeters. Instruments such as ABB’s CoriolisMaster, for instance, can make the necessary conversions and calculations via the flow transmitter, with the output being relayed to the distillery control system.

Summary - the perfect solution for whisky production

With such tight controls on the production and taxation of Scotch whisky, the need to ensure accurate measurement throughout the distillation and custody transfer stages is of paramount importance.

Despite carrying a larger upfront cost than other flowmeter technologies, the performance and operational savings benefits of coriolis flowmeters enable them to eclipse the short-term purchase savings offered by cheaper technologies.

When coupled with their ability to enable accurate calculation of excise duties, coriolis flowmeters offer the perfect solution for whisky production.

Coupled with the assurance of paying the correct levels of excise duties, makes coriolis flowmeters a wise choice for whisky production. ABB offers a range of coriolis meters which are designed to work in a range of processes and applications.  

To find out more, please visit www.abb.com/measurement.

Process Industry Informer

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