Coriolis flowmeters help Scotch whisky producers meet strict regulations

Producing the perfect bottle of Scotch whisky is a complicated business, where 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 ensure that the levels of alcohol in their beverage are exactly right.

Today’s whisky producers must satisfy strict regulations that were implemented over 100 years ago. In 1916, the U.K.’s Chancellor of the Exchequer, teetotaller David Lloyd George, was given the task of finding ways to raise money for the country’s war effort and attempt to curb alcohol consumption. One of the targets for his efforts was the whisky industry. After much protest from whisky producers, a compromise was met that agreed that a standardized strength of 42.9% 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% ABV. This limit still endures 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 subject to strict regulations set down by Her Majesty’s Revenue and Customs (HMRC) in the U.K., the government body responsible for the collection of taxes. These regulations set out various key requirements, with producers obligated 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.

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 liters 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% ABV, which not only maintains alcohol content but also ensures the whisky has the correct taste and aroma derived from its raw materials.

Requirements are equally stringent when it comes to moving the whisky from one place to another. With excise duty on spirits chargeable as soon as they are taken out of warehouse storage, the quantities of whisky being transferred need to be carefully measured to avoid any errors that could increase the amount of duty levied.

Making the difference between Scotch and not

In basic terms, the ABV level of whisky is defined as the number of milliliters (ml) of pure alcohol present in 100 ml 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%, 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 cask process, the alcohol concentration needs to be at a strength of 63.5% 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 liters 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, due to the following:

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 toward 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, and 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 flow rate to be derived.

With zero flow rate, the two sine waves from the pickups 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.