By 1785, thousands of illicit stills were in use across Scotland making inspections, surveillance and prosecution by the Excise officers increasingly difficult. The Board of Excise calculated a still could run a maximum of seven discharges a week. Unable to gauge the daily discharge volume of every still, the Government passed the 1786 Amended Wash Act that licensed Lowland stills' cubic gallon capacity, by charging an annual fee of 30 shillings per gallon, known as the Licensing System. The changes were the catalyst for a handful of innovative Lowland distillers to exploit the regulations with invention.
An English distiller visiting a Leith rectifier in 1788 suggested to the owners, William and John Sligo, to fabricate a 40-gallon flat, or shallow still, for rapid batch distillations to exploit the Act. Sligo’s shallow still was kept secret for a year until Scotland’s largest distilling family, the Steins, learnt of this marvel and exploited this loophole and converted to rapid distillation, minimising duty on their 200-gallon ‘teacup’ shaped stills.
The capital expenditure for this new method of distillation was significant. Less than a dozen Lowland distillers could afford the plant and working capital to operate this intensive process. After 1789, Kennetpans, Kilbagie, Cannonmills, Hattonburn, Dolls, and Craigend engineered and installed shallow stills. When the Government discovered the vulnerability of their new licensing system, the Board of Excise increased the duty per cubic gallon. In turn, distilleries upgraded their technology in response. By 1803, Kennetpans was discharging every three minutes. One distillery was allegedly charging every two and a half minutes. The spirit quality described from rapid distillation as unwholesome, even noxious. A handful of Lowland distillers produced 70 per cent of Scotland’s spirit, shipping it to English rectifiers to compound into gin and brandy.
Each year more sophisticated, more efficient and faster stills were engineered. Feeding these ravenous apparatuses the distillery’s infrastructure needed to accommodate larger volumes. Specially engineered furnaces were constructed to permit fast turnover and better heat control. Local Lowland coal replaced peat as the fuel source. Not only was it cheaper and reliable, it was also six times more energy efficient. Distilling year-round demanded huge amounts of raw materials from grain, yeast and cooperage wood to feed this rapacious production. Puncheons of porter yeast were sent daily from London to ferment the large volumes of wash for the constant charging of the stills. Scottish distilleries began to install steam engines, the first was at Cannonmills in 1787. By the 1790s, rummagers, rotating iron chains were driven by steam engines to prevent scolding of the wash against these fast-heated cucurbits. Soap was added to suppress foaming. Copper plates were inserted into the neck to stop boil-over and puking the condenser. Special flat and zig-zag condensers were invented to cope with the high volume of spirit vapour generated. During this period, famines and high grain prices led to distilling bans and export restrictions, frustrating the distilleries. Distillers commonly used about 25 per cent malted barley to avoid the sixfold increase in the malt tax from 1792 to 1803. The balance was a mash of local bere, unmalted barley, rye, oats, even beans, peas and potatoes.
The Government abolished the Licensing System under the October 1815 Excise Act. In 1823, the revised, landmark Excise Acts of May and July harmonised British distilling regulations under common production standards, measurements and duties. The Government’s regulatory attention was turning to understand a new emergent technology that was about to change whisky production. Applications for column patent stills were registered, and the Board of Excise found this new technology perplexing when evaluating against the existing batch regulations. Not only was this new continuous distillation cheaper, but it also produced a cleaner and high proof spirit. Within a few decades, this silent spirit would usher in the era of blended Scotch.