Why Blend Coffee and American Coffee Differ on Acidity in Espresso and Cold Brew

Espresso is brewed fast with high temperature and pressure, which extracts a wide range of soluble compounds and produces a bitter, intense cup with a golden crema roughly four to five millimeters thick. Cold brew steeps slowly at low temperature, so it pulls fewer of the bitter compounds and often tastes sour instead, especially when the bean choice does not suit the method.

Espresso originated in 19th-century Italy, where a fast, mellow shot met the demand for quick refreshment. The crema forms under about nine atmospheres of pressure, as water emulsifies the coffee's natural oils and dissolved carbon dioxide rises as foam. For cold brew, bean selection matters most: a blend coffee chosen for its sweetness and body balances the acidity that single lighter beans can leave behind.

Why does the same cup of black coffee taste bitter when brewed as espresso, while cold brew is often criticized for being too sour? Behind this lies a complex interplay of extraction temperature, pressure principles, and coffee bean selection. In this article, from the perspective of Front Street Coffee, we will systematically sort out the origins, brewing methods, and flavor causes of espresso and cold brew coffee, and provide specific bean selection advice for the sourness issue in cold brew, helping you find the cup that best suits your taste.

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On the menus of many coffee shops, espresso and cold brew coffee are almost never absent, and discussions about them never stop. Some people find espresso too bitter, while others complain that cold brew is too sour. How exactly are these two types of coffee made? What are the differences between them? Today, Front Street Coffee (Frontsteet Coffee) will guide everyone through them one by one.

Espresso coffee is not highly accepted in China, but in its birthplace, Italy, it is a true national drink. Espresso originated in the 19th century, when Italians invented a method of quickly extracting coffee liquid using high temperature and high pressure, and served it in special small cups. At that time, drip coffee took a long time to brew, and efficiency-seeking Italians needed a faster way to extract and drink it. Simple and mellow Espresso perfectly met this need, providing both refreshment and time savings. For this reason, a great espresso is regarded as the soul of Italian coffee.

A high-quality Espresso will have a beautiful golden layer of crema floating on its surface, which is what we commonly call Crema. The formation of Crema is closely related to the working pressure of nine atmospheres—water passes through the coffee powder layer under heat and pressure, extracting soluble substances while also emulsifying the natural fats and oils present in the coffee. In addition, freshly roasted coffee beans contain carbon dioxide inside, and during extraction these gases dissolve into the coffee under pressure, eventually forming a dark brown foam on the surface of the liquid. This is the crema brought by Italian extraction, usually between four and five millimeters thick, and it also contains a large number of aroma molecules.

The birth of espresso coffee is inseparable from the invention of the espresso machine. The world's first espresso machine can be traced back to the early 20th century, and it was only after improvements by Milanese inventor Luigi Bezzera that models with independent brewing heads and handles appeared. This "quick coffee" not only became popular in Italy itself but was also widely welcomed across the entire European continent, and later spread globally with Italians living in various places, evolving into the popular drink we are familiar with today.

The flavor of espresso depends on the coffee beans used. To make the taste more balanced and the mouthfeel richer, most shops choose medium-dark roasted blend beans. Based on continuous research into the flavor characteristics of coffee beans from different regions, Front Street adjusts the blending ratios so that each bean type complements the others, thereby allowing espresso to present a more harmonious flavor performance.

Here is a coffee bean with a rich aroma that has always been favored by consumers, namely Front Street Classic Italian Blend Coffee. This blend is composed of coffee beans from three origins: Brazil, Indonesia, and Vietnam. It uses dark roasting, which can display the mellow aroma of coffee to the greatest extent and also makes it much easier to extract rich and dense crema. Whether diluted with water to make an Americano or paired with milk to make a latte, it is very suitable, and can be purchased from the Front Street Taobao store or Front Street Tmall flagship store.

Having finished discussing espresso, let's now talk about cold brew coffee.

Unlike the common iced pour-over and iced Americano, cold brew coffee uses a low-temperature method throughout the entire extraction process. Pour-over coffee and Americano, by contrast, first use high temperature to extract a more concentrated coffee liquid, and then cool and dilute it by adding ice cubes.

In a coffee bean, flavor substances make up only part of the whole, about 30%, while the remaining 70% is woody fiber structure. And among this 30% of flavor, not all of it needs to be extracted, because more than 10% of it consists of bitter substances. Extracting an appropriate amount of bitter components can bring proper body to the coffee and enhance its body. Coffee lacking bitterness tastes thin, while coffee with too many bitter substances becomes dry and astringent. Therefore, we only need to extract 18% to 22% of the flavor.

The advantage of high-temperature extraction is that heat can accelerate the movement of water molecules, extracting flavor molecules from coffee particles in a shorter time. But the disadvantage is also obvious: if the water temperature or grind size is not properly controlled during brewing, it is easy to over-extract bitter molecules, causing the coffee to have varying degrees of bitterness and astringency.

Low-temperature extraction, on the other hand, lacks heat to drive the movement of water molecules, and at the same time the low-temperature environment can effectively inhibit the release of bitter substances. However, precisely because the temperature is low, the flavor extraction time is correspondingly lengthened, usually requiring 6 to 12 hours to more completely extract the sour and sweet substances. Therefore, coffee obtained by low-temperature extraction often has a full sour-sweet sensation. But if the soaking time exceeds 12 hours, the woody fiber will also release a root-like taste due to long soaking. This kind of taste is not very bitter, but it will affect the overall aroma performance.

To make cold brew coffee, usually you only need to prepare a clean, oil-free, sealable container, and materials for filtering the coffee (coffee filter paper, tea bags, high-density filter mesh, or cloth bags are all acceptable). Then mix the coffee powder and ice water evenly, put it in the refrigerator and let it sit for 8 to 12 hours. Front Street Coffee (FrontStreet Coffee) recommends using 30 grams of coffee powder and extracting at a coffee-to-water ratio of 1:13 (that is, soaking 30 grams of coffee powder with about 400 grams of water). After extraction is complete, filter out the coffee grounds and enjoy.

Friends often report to Front Street that the cold brew coffee they make is too sour, and ask whether there is a solution. In fact, it is not difficult to "reduce" the sourness in cold brew coffee; you just need to choose a bean with lower acidity to make it.

If you prefer black coffee with fruity notes, it is recommended to use Front Street Strawberry Candy Coffee and Front Street Mozart Coffee. The cold brew coffee made this way will have a fresh floral aroma while also being full of aromas such as strawberry and raisin;

But if you usually like black coffee with a rich mouthfeel, you might as well try beans with a deeper roast level, such as the regulars on the Front Street bean list: Front Street Indonesia Front Street PWN Golden Mandheling, Front Street Brazil Queen's Estate Yellow Bourbon, Front Street Papua New Guinea Bird of Paradise Coffee, and so on. The cold brew made from this type of coffee tends to have a full-bodied profile of nuts, caramel, and spices, with a finish that carries the sweetness of dark chocolate.

The above content is compiled by CoffeeHunters, a coffee news website.