Tag Archives: CoffeeKnowledge

Coffee Cup Shape Impacts on the Taste, Aroma, and Enjoyment

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Last week, I looked around the folks drinking coffee in the cafe and noticed that there was a variety of cup and mugs being used. Not like a coffee chain where every coffee is served in the same type of cup, generally a tall and narrow paper variety. 

I asked how the barista decides on which cup the drink was served in, thinking it could be tied to the needs of that drink. They said they just grabbed the next one available. That was simple enough, but I did wonder about if it would matter to a person enjoying their coffee every day. So, like you know I will do, I dove into it and put down my thoughts to share.

The general first thought was the relationship between coffee temperature and vessel shape is primarily driven by fundamental physics. Tall narrow mugs demonstrate superior heat retention compared to short wide cups due to two key principles. First, the surface area to volume ratio plays a crucial role – wide cups expose more coffee surface to the air, which accelerates heat loss through both evaporation and convection. Second, thermal stratification occurs more effectively in taller vessels, where the hot liquid naturally forms temperature layers with the hottest coffee remaining at the top, while wider vessels promote more uniform cooling throughout the liquid.

The shape of the cup significantly influences flavor perception in several interconnected ways. Narrower openings concentrate coffee’s aromatic compounds in the headspace above the liquid, which enhances the perceived flavor since smell is a crucial component of taste. The different cooling rates between cup shapes affect how flavors develop and are experienced over time, as temperature plays a vital role in flavor perception. Additionally, wider cups expose more coffee to air, which accelerates oxidation and can alter flavor compounds, particularly affecting the more delicate notes found in specialty coffees.

The vessel shape also impacts the physical drinking experience in multiple ways. The ergonomics of drinking differ significantly between shapes, as tall mugs require more head tilt to finish the drink, while wide cups naturally allow more cooling before each sip. The thickness and design of the rim affect both lip feel and drinking comfort. Heat transfer to the hands varies between designs, with narrow mugs concentrating heat transfer to a smaller area of your hands, while wide cups distribute heat more evenly across your palms. This variation affects both drinking comfort and how long you can comfortably hold the vessel.

For espresso-based drinks, the vessel shape influences crema retention – that desirable aromatic foam layer that forms on top of well-pulled espresso. Wider cups cause crema to dissipate more quickly, while narrower vessels help preserve it longer. This is one reason why different coffee styles have traditionally been served in specifically shaped vessels, such as the tulip-shaped cappuccino cup or the narrow espresso demitasse. Each of these classic designs has evolved to enhance particular aspects of the coffee drinking experience.

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The Science of Crema: Understanding the Golden Layer

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Espresso, a complex concoction of water and coffee, is often crowned by a golden-brown layer of foam, known as crema. It’s an integral part of the espresso experience, serving as a sensory preview of the espresso’s quality, and providing aromatics that enhance the overall taste. The science of crema is multifaceted, involving chemistry, physics, and even a bit of art.

The Chemistry of Crema

The formation of crema begins at the cellular level of the coffee bean. Coffee beans are composed of about 800 volatile compounds, including lipids, proteins, sugars, and carbon dioxide. When coffee beans are roasted, a process known as the Maillard reaction occurs, which leads to the creation of even more volatile compounds, along with the rich brown color of the beans.

When the hot water meets the ground coffee in an espresso machine, it extracts these volatile compounds. The high pressure forces water through the coffee grounds, which extracts oil droplets encapsulating some of these compounds. This oil is crucial to crema formation.

The pressurized water also liberates trapped carbon dioxide gas within the coffee grounds. The CO2 wants to escape and forms bubbles. These bubbles get coated with the oil droplets, effectively creating the crema.

The Physics of Crema

The high pressure used in espresso machines, usually around 9 bars or 130 PSI, is key to the creation of crema. This high pressure helps to dissolve more CO2 from the coffee grounds into the water. When the pressure decreases as the espresso shot is pulled, the CO2 comes out of the solution, forming tiny bubbles.

These bubbles are stabilized by the oils and compounds extracted from the coffee. The oils form a thin layer around each bubble, preventing them from bursting too quickly and helping to create that desirable, persistent crema layer.

The Art of Crema

The quality and quantity of crema can be influenced by several factors, including the freshness of the coffee, the grind size, the roast profile, and the extraction method.

Fresh coffee tends to produce more crema because it contains more CO2. As coffee ages, CO2 gradually escapes, which means less gas is available to create those bubbles.

The grind size is also important. If the grind is too coarse, water will pass through the grounds too quickly, not extracting enough oils or CO2. If it’s too fine, the water may not be able to pass through at all. The perfect grind size for espresso is often described as being like fine sand.

The roast profile can affect the crema too. Darker roasts typically produce more crema due to the longer roasting process, which creates more oils. However, lighter roasts might produce crema with more complex flavors, as they preserve more of the coffee’s inherent flavor compounds.

Crema is a complex combination of coffee oils, volatile compounds, and CO2 bubbles. It’s a fascinating subject at the intersection of chemistry, physics, and art, where understanding the science can lead to a better appreciation of the beauty and taste of a well-crafted espresso.

Please note that if you purchase from clicking on the link, some will result in my getting a tiny bit of that sale to help keep this site going.