What is a nitro beer?
Not so much a beer variety, more a special technique to create a very distinctive drink. A nitro beer differs from a usual brew in that carbon dioxide (which occurs naturally in the brewing process, and is also often added at the bottling stage) is partly replaced with nitrogen gas.
You’ll instantly recognise the results: a cascading effect as bubbles in the liquid appear to be falling rather than rising, a creamy white head and a velvety taste. You can increasingly find both ale and lager nitro beers in many pubs and bars – but the most famous is a stout, and from the brewery that pioneered the technique, Guinness Draught.
Know Your Beer - Nitro
Know Your Beer - Nitro
The history (and science) of nitro beer
Watch a glass of Guinness Draught being poured and it looks like alchemy at work – bubbles seemingly defying gravity, a long mesmeric settle and surge of black and white. What you're witnessing, though, is not magic but pure science, the fruits of many years of brewing innovation.
In the early 1950s, British mathematician and brewer Michael Ash, and his team at St James’s Gate, worked on a pouring system to produce, and easily reproduce, a perfect pint of Guinness on tap. Ash’s solution was to harness the properties of an element born in the stars, in the very heart of a supernova: nitrogen.
At 78% it is the most abundant gas in Earth's atmosphere, and is largely insoluble in water. This property leads to two effects when infused with beer: firstly, its bubbles are smaller and more stable than carbon dioxide, which are interpreted by receptors in our mouth as having a smooth and velvety feel.
Secondly, the stable bubbles, coupled with the type of protein in the barely wheat used by Guinness, make for a longer-lasting beer head. Carbon dioxide, on the other hand, is a much more volatile gas in water, meaning its bubbles pop quicker, and your beer head vanishes quickly as a result.
When Ash and his team revealed the first nitro stout in 1959, to coincide with the 200th anniversary of the signing of the lease at St James’s Gate, they had not only created the perfect draught pint of Guinness, they’d also essentially crafted a new type of beer.
Nitro: frequently asked questions
Why do the bubbles in a Guinness Draught travel downwards?
In nitro beers, such as Guinness Draught, drinkers are often left perplexed by how its bubbles appear to defy the laws of physics by travelling down not up. What they are witnessing though is a actually a flow of tiny stable bubbles of nitrogen around the glass.
When the beer is first poured, some bubbles will stick to the side of the glassware, slowing rising ones around it, while bubbles in the centre of the drink can flow faster, unimpeded. This has the effect of creating a circulating current with a central column of bubbles going up, pulling others, and the ones visible to the drinker, downwards.
Eventually this leads to the forming of the beer head and, as bubbles nitrogen are more stable, one that’s creamy and long-lasting, be that on the top of your drink or on your top lip.