The creamy head produced on pints in pubs and bars comes about through the dispensing process which introduces nitrogen into the product. Replacing carbon dioxide, nitrogen has different characteristics producing tighter `nucleated’ bubbles to form the familiar foaming head.
Reproducing the creamy head on drinks at home remained impossible until the advent of the widget. This simple plastics device, introduced in 1989, had a number of disadvantages, among them its temptation to over-foaming on being opened and the fact that unless kept under refrigeration, they were subject to creep.
As a result two companies, Whitbread and Heineken, embarked on a collaboration to refine and develop widget technology. Its objective was to create a floating device, made in aluminium which was also capable of being used in bottles. The outcome was the draughtflow widget.
The original widget was made of plastic, fixed to the bottom of the can and relied on pasteurisation to make it work. The draughtflow widget floats on the top of the beer, and as it is smaller, leaves more space between the contents and the top of the can. This extra space making over-foaming less likely.
The can widget is made of aluminium apart from two plastic one-way `duckbill’ valves. The bottle widget functions in a similar manner, but is smaller and made of plastic to enable it to pass through the narrow bottle mouth.
After filling oxygen is removed and liquid nitrogen is dosed on top of the beer which evaporates after the container is sealed, building up the pressure in the headspace.
On opening the headspace pressure escapes and the widget jets nitrogen through the lower duckbill valve into the beer. This causes a break-out of dissolved nitrogen and carbon dioxide, creating a small quantity of foam in the headspace. As the beer is poured into a glass this foam enters the glass first and as the rest of the beer is poured on the foam, `seeding’ begins, creating the characteristic creamy head.
Whitbread Technical Centre Tel: 01582 391166