Sezeryadigar / Getty ImagesOptimized Brazilian tulip glass, with trumpet mouth to keep the beer colder for longerSezeryadigar / Getty Images
Unlike many others who drink their beer at higher temperatures, the overwhelming majority of Brazilians like it ice-cold. With this preference in mind, mechanical engineer Cláudio Pellegrini, of the Federal University of São João del-Rei (UFSJ), Minas Gerais State, applied knowledge from his fluid mechanics specialization to determine what glass format would keep the beer as cool as possible while being consumed.
Mathematical modeling results produced a type of general rule—to be validated—that could be adapted to any type of glass (tulip, pint, or mug/tankard), provided that the main aim of the receptacle is to keep the liquid cold for longer: the circumference of the glass should increase progressively from bottom to top. With a narrow base, the diameter only increases in the direction of the wider mouth, and applies a growing mathematical function known as monotone (or monotonic).
The general rule is exemplified by a tall glass with the so-called trumpet mouth, which makes for less heat exchange between the liquid and the atmosphere. Except for its top, where the trumpet mouth is located, the glass has straight lines along most of its length. Drinking vessels that bulge at their base or halfway up, such as those similar to the Brazilian tulip, are not ideal for keeping the beer cold for longer, according to the study.
Pellegrini used equations to describe the heat transfer between the glass and the atmosphere over time to define what curvature would be most effective in minimizing this process. The analysis included a dynamic aspect of the system: heat transfer is reduced as the amount of beer in the glass decreases on consumption. Trumpet-mouth glasses minimize thermal exchange because the beer remains at the base, which is narrower and has a lesser area of contact with the atmosphere, for longer.
“The study could be used to guide the manufacture of more effective glasses, as it points to a design not currently produced,” says the mechanical engineer. Of the better-known commercial models, the Pilsen-type glass (tall with a wide mouth and small base) is probably the closest to the ideal model. In October last year, Pellegrini shared a preprint (unpublished article not yet peer-reviewed) on the arXiv repository about the study. The text updates and develops an approach presented in a 2019 article published in the Revista Brasileira de Ensino de Física (Brazilian Physics Education Journal).
In a previous article, without having fixed the dimensions of the modeled glasses, Pellegrini arrived at solutions of little practical use: the ideal glasses to keep beer colder for longer had a capacity of between 2 liters (L) and 103 L. The approach outlined in the current study included more specific details on the receptacles. The researcher used fixed dimensions for classic types of glasses, such as the US pint, capacity 473 milliliters (mL), the Brazilian tulip (300 mL), and the mug/tankard (473 mL). He also defined the basic parameters of their geometry: the height of the glass and circumference of the base and mouth. With these adaptations, the new study presents solutions close to reality. The modified Brazilian tulip glass design that illustrates this report is one of those.
To mathematically model the problem, Pellegrini employed certain ideal suppositions to conceive the glasses. Head (that foam at the top), which helps keep the beer cold, and heat transfer by hands touching the glass, were disregarded. Calculations were focused on the heat passing through the side of the glass and what enters from above due to contact between the air and the beer. The bottom of the glass was designed to be isolated from the outside environment (thicker glass) and the liquid temperature considered as homogenous.
Pellegrini focused only on glass receptacles and not those with thermal isolation, which have become popular in recent years. The most famous of these, the Stanley cup, uses a well-known, effective design: the thermal isolation provided by the vacuum between the inside in contact with the liquid and the outside in contact with the atmosphere.
The article is very humorous, and full of witty remarks. Considering the US-style glass, very common in Brazilian bars, Pellegrini concluded that the beer is kept cold by the most primitive process. “Due to the low capacity [of the glass], the beer is consumed so quickly that there’s no time for it to warm up,” he says. This statement gets a footnote: “And no, you don’t know anyone who drinks that slowly,” he jokes.
Physicist Peter Schulz, of the University of Campinas (UNICAMP), welcomes Pellegrini’s work. “It’s a very pleasant surprise,” he says. “Science can take itself too seriously, and the article speaks to a general desire to unstiffen scientific studies a little.” Vanderlei Bagnato, a graduate physicist from the University of São Paulo (USP), now at Texas A&M University, says that the study indicates how creativity can be used not just in the production of new science, which advances the frontiers of knowledge, but also to solve day-to-day issues using existing knowledge. “Though it doesn’t generate science, the article shows the value of knowledge to optimize our daily lives,” Bagnato comments.
The UFSJ researcher also points to another reason for applying himself to such an apparently banal theme. “Young people have not shown interest in areas of knowledge that have little practical application,” says Pellegrini, 33 years a professor. That’s why he conducted an educational study; he purposely avoided using computer simulations and experiments to indicate how heat transfer can be used to obtain the answers to simple questions, with a strictly analytical approach. It worked.
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