The South African Breweries has brought to market its first nitrogenated draught in a can – Castle Milk Stout Ultra Smooth. Created to give a sensory effect and a special theatrical moment during pouring, Castle Milk Stout has tight and creamy foam and a smooth sensation in the mouth thanks to a balance of nitrogen and CO2 gases.
Most beers are pressured with carbon dioxide, which gives them their sharp, effervescent quality. A nitrogenated beer is pressurised with a mix of nitrogen and carbon dioxide. This causes the beer to take on a creamy mouth feel, with its sweeter aspects drawn to the forefront.
Drinking a nitro-charged beer in the comfort of your own home is not just something which happened overnight. Rather, the beer gurus at The South African Breweries worked their magic to recreate the high pressure which beer on tap has. This activates the nitrogen gasses and causes the beer to bubble. "Understanding gas dynamics was our greatest learning," said Frieda Dehrmann, Consumer Science and Sensory Manager for SAB.
Rather than using a disruptive device placed inside the beer to manage the characteristics of the beer's head, Ultra Smooth is pressurized by the addition of liquid nitrogen, which vapourises and expands in volume after the beer is sealed. "Some nitrogen dissolves in the beer which also contains dissolved carbon dioxide." Dehrmann said it was vital that oxygen be eliminated from any process developed as this could cause flavours to deteriorate. "The presence of dissolved nitrogen allows smaller bubbles to be formed, and this is what increases the creaminess of the head. Smaller bubbles need a higher internal pressure to balance the greater surface tension, which is inversely proportional to the radius of the bubbles. "Achieving this higher pressure would not be possible using just dissolved carbon dioxide, as the greater solubility of this gas compared to nitrogen would create an unacceptably large head," she said.
It is the two magic words of "pour hard" which the consumer really needs to listen to, otherwise the beer would just lie there in the glass, appearing flat and lifeless. To do this, the can should be inverted and held in a 180˚ angle over the beer glass, emptying the contents as quickly and roughly as possible.
Castle Milk Stout general manager, Julian Remba, said there were four steps to ensuring Ultra Smooth was served correctly. "Firstly, the beer should be chilled to its utmost and served in a pint glass, large enough to enable one pour with no top-ups. Ultra Smooth should be poured with a 'hard pour' - not in the usual careful way in a tilted glass. This is to ensure enough motion of the liquid to guarantee the surging of the gas bubbles, he said. After this, pause to allow the beer to settle and then sip and enjoy the creaminess on your lips.
"Castle Milk Stout Ultra Smooth is made from quality dark roasted malt, and due to its special fermentation process, provides a rich, smooth and satisfying taste experience."
Dehrmann explains further: "The fermentation is especially designed and tailored through what we call an arrested fermentation. With this process, the recipe has designed the perfect balance of malt and fermentation flavours that gives the unique smooth creaminess of the Milk Stout style."
Because Castle Milk Stout is much smoother than most beers, and contains less carbon dioxide than regular beers, it is the perfect drink with a rich oxtail stew, or with a delicious dessert. Paired with a chocolate mousse, or sticky toffee pudding, or Tiramisu, the smooth sensation of Ultra Smooth is their perfect companion. "It can be enjoyed with a cheese, dried fruit and nut platter as the perfect balance between smooth and creamy, at the end of a meal."