The Science Behind Guinness's Foam: Why It's Essential

There is a specific way to pour and drink a Guinness beer. The two-part pour method dates back to the 1930s when Guinness beer came in two types of casks. The first part involves filling a glass three-quarters full, and the second part involves topping it off. The two-part pour is necessary because if the glass was filled in one fell swoop, the head would be too big. The foam is an essential part of the beer, as it is a nitrogen cap that protects the flavors underneath from being oxidized. The nitrogen also gives the beer a smooth and velvety texture.

The two-part pour

In 1951, Guinness hired a mathematician-turned-brewer, Michael Ash, to solve this problem. Ash saw nitrogen gas as the solution as it is inert and already makes up three-quarters of the air we breathe. After much testing and research, Nitro Guinness Stout was launched in 1959 to coincide with the brewery's 200th anniversary.

Despite the development of this new method, Guinness leaned into the two-part pour, developing a training protocol, step-by-step guide, and special handles. They also unleashed a series of groundbreaking ad campaigns touting the message that good things come to those who wait, further adding to the mystique of the pour.

Today, the two-part pour is still widely used, with 90% of American bartenders knowing that something different must be done when pouring a pint of Guinness Draught Stout. While some may argue that it is just a marketing ploy, others claim that it allows for a denser, creamier beer and highlights the beauty of the beer as it changes from a creamy light brown to a dark ruby red.

Whether it is truly necessary or not, the two-part pour has become an iconic part of the Guinness drinking experience, with many believing that it enhances the flavour and presentation of the beer.

The nitrogenation process

Nitrogen is largely insoluble in liquids, which contributes to the thick mouthfeel of nitrogenated beers. This effect is enhanced by the use of a restrictor plate, a special piece of tap equipment that forces the beer through tiny holes before it lands in the glass. This process creates the distinctive "rising" effect, with nitrogen bubbles rising slowly to the top of the glass, resulting in a dense, creamy head.

The use of nitrogen in beer has several benefits. Firstly, it creates a smoother and creamier taste and mouthfeel due to the smaller gas bubbles produced when nitrogen interacts with the beer. Secondly, nitrogenated beers are less carbonated and have a less acidic flavour than their carbonated counterparts. The creamy head and lower carbonation levels give nitrogenated beers a unique, smooth mouthfeel, even when the beer itself is light or thin. Additionally, the absence of oxygen gas in nitrogenated beers allows them to retain their flavours for longer as oxidation is minimised.

The perfect head-to-beer ratio

When it comes to Guinness, the foam is an essential part of the drinking experience. The creamy, almost white foam that makes up the beer's head is crucial to its enjoyment and should be embraced, not slurped off.

The ideal head-to-beer ratio for a Guinness is about 0.5 to 1 inch of foam. This may vary slightly depending on the style of beer and personal preference, but a good rule of thumb is to aim for a head that is thick enough to create a creamy texture and enhance the aroma of the beer without being too dominant.

When pouring a Guinness, it is important to follow the proper technique to achieve the perfect head-to-beer ratio. For a draught Guinness, the glass should be tilted at a 45-degree angle while pouring the first two-thirds of the beer. The glass is then placed on the bar and allowed to settle before being filled the rest of the way with the glass held straight up and down. For bottled or canned Guinness, a similar technique is used, but the beer is chilled beforehand, and the glass is also ideally chilled.

Achieving the perfect head-to-beer ratio is not just about the pouring technique; it also has to do with the ingredients and brewing process. The protein content of the beer, which comes from the grains and hops, plays a crucial role in head retention. Additionally, the hops' polyphenols help to retain foam bubbles at the top of the beer. Brewers may need to experiment with different ingredients and techniques to find the perfect balance for their Guinness.

The glass shape

The tulip-shaped glass features sloping walls that affect the currents in the beer, either separating or accumulating the bubbles. This variation in density creates flow, impacting the overall settling time. While the tulip shape is iconic and traditional for Guinness, Professor Lee suggests that an ideal glass shape would be more like a giant martini glass with sloping walls, which would potentially reduce settling time.

The official Guinness pint glass is a 20-ounce (568ml) tulip-shaped glass, often featuring the classic gold harp and Guinness logo. These glasses are designed to ensure the perfect pour, with a shape that complements the beer's unique characteristics. The glass is also an important part of the Guinness drinking ritual, contributing to the overall experience and enjoyment of the beer.

When drinking a bottled Guinness, it is recommended to drink straight from the bottle as each bottle is equipped with a "rocket" that releases gases to create the signature creamy texture. For canned Guinness, it is recommended to pour the beer into a glass, preferably chilled, at a 45-degree angle, similar to pouring a draught Guinness.

The drinking technique

Drinking Guinness from a tap

The two-part pour is the Guinness-approved method for pouring the perfect pint of Guinness from a tap. First, the bartender fills a pint glass from the tap to two-thirds of the way full, tilting the glass at a 45-degree angle while pouring. Then, they place it on the bar and walk away. After a few minutes, the beer is filled the rest of the way with the glass held straight up and down rather than at an angle. The two-part pour is done to control the size of the head, as a one-fell-swoop pour would create a head that is too big.

When drinking a freshly poured Guinness, it is important to wait until you can see a clear division between the white foamy head and the dark black beer. If the beer in your glass still looks murky and brown, the Guinness isn’t ready. When drinking, grab the pint and gulp down at least a quarter of the beer. Now take three more sips. There should be only four foam lines in the glass when you’re done.

Drinking Guinness from a bottle

The first rule of enjoying a Guinness from a bottle is to not pour it out. Each bottle is equipped with a "rocket," which is activated when the bottle cap is removed. This rocket releases a mixture of gases as the drinker tilts the bottle to their mouth, creating the signature creamy texture of Guinness Draught. If poured into a glass, the Guinness will lack foam and be lacklustre in flavour.

Drinking Guinness from a can

Guinness in cans has a spherical widget inside that releases pressurized nitrogen during the drinking process to mimic a nitro draft pour. When the can is opened, the pressure within the aluminium drops to match the pressure in the room. As the pressure within the widget is still higher than the beer around it, tiny bursts of nitrogen are released into the liquid, providing the brew with Guinness’s classic creamy head.

When drinking Guinness from a can, it should be poured into a glass prior to the first sip. Brewers at Guinness suggest the beer be chilled to approximately 46 degrees Fahrenheit. Then, the glass should be tilted at a 45-degree angle before slowly pouring the beer from the can until the glass is three-quarters full. Then, let the beer settle for a few moments before pouring the remainder of the beer directly into the glass. Before enjoying, allow the beer to settle further until the white head has completely separated from the dark beer.

Frequently asked questions