What is Espresso Crema? Should we keep the Crema or not?
Espresso is a complex beverage, composed of many different levels, typically Crema – an integral element of Espresso. Many people like Espresso Crema, some dont, they think that the concept of Espresso with a nice and smooth Crema layer is an outdated standard. So what is Espresso Crema and is it crucial to keep the crema?
What is crema?Crema in Italian means ice cream, and it is a natural floating bubble formed on the surface of coffee, similar to the foam on a beer glass.
Crema – Surface layer of EspressoCrema formation: When pressed, water at high pressure dissolves more CO2 – the gas that accumulates inside coffee beans during roasting. After the end of the extraction time, the solution (Espresso) returns to normal pressure and forms extremely small air bubbles. These bubbles form on the surface of the solution and form a floating foam.
What does Crema tell us?For a long time, the Crema class was considered important. But in fact, Crema shows two things. First, the fresher the coffee is, the less gas it has left over after roasting – so the less bubbles appear. The second is your strong or weak cup of coffee. The darker the color of the foam layer indicates, the stronger the coffee. This is explained as follows: Coffee is just a layer of foam floating on the surface of the solution, and there is a lighter color because the air bubbles reflect light, so the color of coffee will determine the color of the Crema layer. Therefore, dark roasted coffee also has a more colored crema layer.
Espresso CremaAfter all, the Crema class cannot tell you whether or not the coffee beans are of a good quality, or if they are carefully roasted, or whether the broth is suitable – what makes a cup of coffee tasty. A cup of Espresso with a smooth, long-lasting brown-yellow crema always catches the eye of a drinker more than an unsustainable crema. So how can the sustainability of the espresso crema be made? Refer to the following tips offline. Espresso Crema is not just a drink; it is also an art.
Espresso Crema is a form of art
The unknown facts of Crema in Espresso
Crema in generalWhile coffee experts use crema to assess the quality of Espresso extract. For example, crema indicates whether all parameters that affect the extraction process, such as degassing time, grinding level, pressure mechanism, are correct when extracting a coffee cup. Most consumers prefer the presence of a nice layer of crema on the cup, some will spoon it into the cup, and some will rotate the cup to save the crema for the last sip of coffee. All sensory elements from the image of the crema are used to create the expected taste of an Espresso cup with the expected balance of flavors. Although the dark brown or tiger skin color Crema and the velvety of air bubbles are “characteristic” of a desirable Espresso, they are only a minor sign of a good extract and behind the taste of the coffee. Finally, for most baristas, the formation of crema is a craft rather than a science. A neatly placed layer of coffee in the basket allows high-pressure water to flow along with the carbon dioxide (CO2) present in roasted coffee and the carbonate present in the water, which is a key factor in the formation of crema. Quite simple, but most baristas choose to adjust the grinder and manipulate techniques such as grooming and tamping to optimize the extraction process and obtain the most delicate crema layer. However, the question is what is the effect of color, bubble size, and number of crema on the coffee experience? Is there a crema that is optimal or a feature of crema in evaluating coffee sensory perception in general? We need to answer these questions before we can think about how to extract the perfect Espresso. As a first step, it is important to understand the physical and chemical aspects of crema and how we can refine the properties of crema to optimize its quality. To do this, we need to distinguish crema formation from the stability of crema.
Crema formation and stabilityThe process of crema formation can be considered a complex and challenging phenomenon for those who do not like science, but if you like beer – the foaming mechanism of these two drinks is the same to 85 %, includes four main stages:
- Bubble Formation: The formation of bubbles occurs when CO2 is released from the espresso extract from the supersaturated state at the nucleation positions in the glass – in Espresso, the nucleation position is from the microscopic fragments of the coffee bean in the extract.
- Bubble rise: Light pouring process and low surface tension of the extract promote the formation and increase of smaller bubbles, creating a more stable cream foam.
- Drainage: After forming, bubbles begin to drain due to the effect of gravity, they gradually shrink and burst.
- Disproportionation: In parallel with drainage, the reduced surface tension causes small bubbles to merge into larger, more unstable and fragile bubbles.
Crema formationThere have been several attempts to describe how crema forms in Espresso. And according to academics, that when the water is forced through the coffee under great pressure, it causes the emulsification of coffee oil in the extract – because the oil nature cannot dissolve in water but due to the large pressure The oil is broken down to microscopic size and can disperse in water. This emulsification system, combined with the amount of CO2 (these gases are retained in the cell structure of the grain during roasting and compressed by high pressure) create the crema layer we are talking about. In fact, the longer the coffee is exposed to high pressures, the more CO2 it will release, and the thicker the crema layer will be. However, CO2 also impedes the flow of water in diffusing the flavors contained in the seeds. Therefore, during the whole process of preserving coffee to make Espresso, we always try to balance the freshness of coffee just enough to create crema. Another study found that the super-saturated condition of CO2 in coffee is a possible motivation for crema formation in Espresso. More specifically, the water-soluble CO2 concentration at pressure and normal temperature will be lower than the CO2 solubility during extraction at high pressure (9 bar) and with a water temperature near 100 ° C. This process of dissolving CO2 in water at high pressure and temperature causes CO2 oversaturation in coffee extract and leads to the nucleation of small bubbles after the phase transition from high pressure to environment pressure (when the high-pressure extract exits the coffee and enters the cup). This effervescence effect can be observed immediately after making Espresso and it is similar to when you open a beer or champagne. But in the case of Espresso due to the small volume with the height of the liquid limit of about 1.5-2 cm, only small bubbles can be formed in the crema – instead of large bubbles like in beer or champagne.
Factors affecting crema stabilityAfter the crema is developed, instability usually occurs through three steps, before it completely dissolves. The first is a combination of bubbles close together, which occurs when the membrane separating the bubbles collapses. Second, following the Ostwald ripening process, due to the pressure difference, the small bubbles are close and merged into the larger sized bubbles. Finally, gravity forces the liquid to separate from the air bubbles. This in turn makes the crema thinner. Although these phenomena occur the same in any Espresso cup, the high-temperature effect and the way it cools from the top-down adds complexity of the physical phenomena in the creation and stability of crema. On the other hand, many studies have shown that the lipid content can also affect the stability of the foam (as stated before, the lipid is insoluble in water, it always seeks to separate from the water leading to instability of crema). In a regular Espresso (25 ml), total lipid levels range from 45-146 mg for Arabica coffee and 14-119 mg for Robusta coffee (completely pure). In other words, Espresso from Arabica coffee contains a higher total lipid content than Espresso from Robusta, and therefore the probability of instability induced by lipids is higher for Arabica.
Water temperature & qualityA number of previous studies have suggested that the relatively high temperature of an Espresso can negatively affect the stability of the crema. The main reason is that volatile water reduces the distance between the steam bubbles and causes the foam to collapse quickly. Finally, the stability of Crema on espresso has also been shown to depend on water hardness (The Craft and Science of Coffee). In particular, changes in ionic content or interaction between cations and protein/polysaccharide complexes will lead to instability of the foam formation mechanism.
Chemical basis of cremaNot much detailed research has been published so far on the chemical compounds responsible for the formation and stability of Espresso crema. Some studies show that the quality of crema depends on the amount of protein in general in the extract. Cream stability is found to be related to carbohydrate components such as galactomannan polysaccharide and arabinogalactan. Other dependent variables observed were total dissolved solids, pH, lipid, protein, and carbohydrate. A strong correlation was found between crema stability and high molecular weight compounds, including complexes between polysaccharides, proteins, and phenolic compounds caused by roasting.
Why does Robusta coffee help make crema better?Recent empirical studies on the crema ingredients & activity have yielded new insights into the molecular structure of the compound responsible for crema formation. Thereby, scientists have discovered that the Sucrose Ester group (1) and the 4-vinylcatechol oligomers group (2) are the two main active components of foam in the coffee crema (Kornas data and Hofmann et al.).
- Sucrose ester or sucrose fatty acid ester is a natural product in green coffee and decomposes gradually when roasted with increasing roasting time.
- Caffeic acid is the main cause of the intense and characteristic bitterness of Espresso coffee, during roasting, CGA decomposition reaction will initially form caffeic acid and release 4-vinylcatechol. Therefore it can be said that oligomers 4-vinylcatechol is a secondary product created with increasing time.