The Hard Shake
Perversely the hard-shake is not hard, it’s gentle; although this choreographed shake is hard to master. Invented by Japanese bartender, Kazuo Uyeda, the hard-shake is a stylised way of shaking a cocktail intended to drive the ice inside around the shaker rather than simply back and forth crashing into either end.
Practitioners of the hard-shake hold the shaker in a slanted position out in front of their body with elbows held high. The shaker is pulled back and forth on a horizontal axis while their arms are simultaneously raised and lowered on a vertical axis, snapping the wrists and twisting the shaker. It's quite a show - the martial arts of bartending.
Proponents of the hard-shake maintain that the method produces a better tasting cocktail. They go as far as to say that different motions of hard-shake produce different bubbles and so the style of hard-shake should be changed to better suit certain cocktails. Enter the '2-step', '3 step', '4-point', '8-point' and 'butterfly' styles of shaking. These hard-shake styles are said to reduce collisions between the ice and the internal walls of the shaker.
Theoretically this avoids breaking up the ice so controlling dilution, increasing aeration and shapes the ice shards produced. A hard-shake should leave circular ice inside the shaker and practitioners of the hard-shake tend not to fine strain, aiming to leave fine shards of ice floating on surface of the cocktail. [Something I'm not a fan of.]
When it comes to the science of shaking I recommend you turn to Dave Arnold of the French Culinary Institute in New York. Back in 2009 he published results from a series of experiments which prove no matter how you shake and pretty much whatever kind of ice you use, as long as you shake vigorously for 12 to 15 seconds, you'll produce a drink between -5°C and -8°C (differences mostly dependent on construction of shaker and its temperature) with very much the same dilution. Dance around as much as you like but different shaking techniques make no difference to the end temperature or dilution.
Sadly bubbles are somewhat harder to measure than either temperature or dilution and shaking does aerate cocktails giving a mouthfeel that is softer than if the same drink is stirred. How the motion of shaking affects the size and numbers of tiny air bubbles in a cocktail is debatable and much debated, but what the eyes tell the brain has a big influence on the perception of how a drink tastes.
Good practitioners of the hard-shake show the customer that they are employing considerable skill, effort and care to craft a cocktail. Much more than simply pouring three or four ingredients into a shaker, giving it a quick shake and straining it into a glass. Perhaps the perception that the hard-shake produces a better tasting cocktail has little to do with bubbles and a lot to do with theatre.
Whatever. Please fine strain my cocktail.