Isn’t it one of the most amazing sounds of summer? The sound of the fizz or the one when the can pops open? But its popularity sure doesn’t stop the beer or the fizz from coming out.
The refreshing hissing sound on opening a can of an aerated drink is caused by the gas bubbles that try to escape from the bottle due to the insolubility of CO2 in it. This is caused due to the change in the pressure for bar 3 to 1 on opening the can at atmospheric pressure. Co2’s solubility in water reduces and comes down to as much as -3 form -4.5 at atmospheric pressure, the phenomenon described in Henry’s Law.
The microscopic gas bubbles attach themselves to the inside of the can (nucleation) before it is opened. On the opening of the can, these bubbles increase in number due to lack of solubility of CO2. When these bubbles reach a definite size they separate from the inside of the can and rise up to the top of it due to buoyancy. Displacing liquid on their path.
Here tapping the top of the can plays its part. This technique works or not is a debate but there are studies that state, it may. As described earlier, the bubbles in the can nucleate at the walls so tapping can dislodge the bubbles, allowing them to float on the liquid.
The bubbles expand in size when the can is opened, with those deeper in the liquid travelling to the top and those shallower on the surface, displacing more of the liquid and resulting in larger amounts of liquid being cast out. A “tapped” can will have less “deep” bubbles and so less liquid will be casted out – and possibly sprayed out – than an “untapped” can.
Bubbles can also be dislodged from the side of the can with intense shaking, this method presents more hurly-burly which increases the energy in the system, causing more bubbles in the drink and more squirting when opened. Tapping the top of beer bottle with another has a similar effect, resulting in a colossal outburst of beer foam. This is because of the “mushroom clouds” created inside the bottle that gush huge quantities of liquid as they escape.
Glass and gushing
The debate of tap on top aside, the actual material that forms the container may also reduce gushing. Studies say that the amount of foam formed when beer is poured into glasses of different “wet abilities” explaining the extent to which water wets a material.
When it comes to the level of gushing another important factor is the stabilization of the bubbles which is caused by the presence of large molecules in the drink. This is the reason why some beers have long-lived foam heads. Such foam stabilizing agents are a conversation for another day.
This summer try different ways to open your fizzy drink – and see how much of it ends up on you!
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Author: Technology and Beyond
