Must Dirty Coffee Be Served in a Chilled Glass? How to Create Perfect Layers in Your Dirty Coffee?

The Rise of Dirty Coffee

As a viral "internet-famous coffee" in recent years, Dirty has successfully secured its place on the regular menus of many specialty coffee shops with its stunning appearance and highly distinctive flavor profile.

The Question of Chilled Glasses

When it comes to making Dirty, many tutorials emphasize three key elements: there must be distinct hot and cold layers, chilled glasses are essential, and Boeck milk is the best choice. FrontStreet Coffee has previously explored the layering effect and Boeck milk usage in separate articles. But are chilled glasses really that important?

With a learning attitude and experimental spirit, FrontStreet Coffee conducted a comparative test today using room temperature, refrigerated, and frozen glass cups. Using cold milk (Guangming Fresh Ranch) as the base and finishing with espresso, we wanted to see whose "dirty" effect was best and whose hot-cold layering lasted longer.

Experiment Results

For this experiment, FrontStreet Coffee used 20 grams of coffee powder extracted for 27 seconds for all cups. The Dirty effects produced in cups at different temperatures were as follows:

Room Temperature Glass Cup

The cup temperature was higher than the milk, showing distinct layering with a gradual "dirty" effect. When tasting the first sip, the temperature difference between coffee and milk was less pronounced. By the second sip, the milk began approaching room temperature.

Refrigerated Glass Cup

The cup and milk temperatures were nearly identical, with a larger color buffer zone and stable, persistent layering. The hot-cold temperature difference was clearly noticeable during the first two sips. After 3 minutes, the crema dissipated, and after 5 minutes, it began approaching room temperature.

Frozen Glass Cup

The cup temperature was lower than the milk, with less color difference in layers, but the visual effect of coffee "staining" the milk appeared most "dirty." Compared to the first two groups, the frozen glass Dirty maintained more complete crema, had the most distinct hot-cold layers, and remained drinkable for longer. Unfortunately, since the glass cup was taken from below-zero temperatures, ice crystals on the cup wall formed many small water droplets, reducing transparency and making it less photogenic than the first two groups.

Analysis and Recommendations

It's not difficult to see that regardless of whether the cup is pre-chilled, as long as the milk quality is sufficient to support the coffee liquid, Dirty can form beautiful layering effects. The lower the cup temperature, the better the chilled milk texture, creating a more excellent experience when combined with warm, aromatic coffee liquid.

In fact, Mr. Katsuyuki Tanaka, the original creator of Dirty, did not include "chilling the glass" when making this dirty coffee. In 2009, Mr. Tanaka opened a café called Bear Pond Espresso in Tokyo's Kitashimosawa, and Dirty was a specialty product he created from the beginning, listed on the menu as B.P. Dirty.

The most distinctive feature of Mr. Katsuyuki Tanaka's B.P. Dirty is his unique espresso— "Angel Stain." He specifically uses a bottomless portafilter for extraction, observing and judging the espresso extraction with his eyes, as the espresso leaves tear-like traces on the cup wall. With the combination of dark roast, large coffee dose, ultra-high concentration, and low extraction rate, the double "Angel Stain" allows the B.P. Dirty's coffee liquid to sink slowly, maintaining persistent layering even without pre-chilling the glass.

In summary, if you seek both a photogenic Dirty with high visual appeal and a distinct layered tasting experience, FrontStreet Coffee recommends pre-chilling the glass cup in the refrigerator along with the milk, removing them only when ready to prepare. If you want to experience the charm of espresso and crema, try to take photos within 3 minutes, otherwise you'll miss this Dirty's optimal tasting window.

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