Crema Espresso Should we keep the crema or not 0
Espresso Knowleadge

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people like Espresso Crema, some dont, they think that the concept of Espresso with a nice and smooth Crema layer is an outdated standard.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.
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Crema – Surface layer of Espresso

Crema 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?

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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.
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Espresso Crema

After 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.  
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Espresso Crema is a form of art

 

The unknown facts of Crema in Espresso

Crema in general

While 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.
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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 stability

The 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:
  1. 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.
  2. 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.
  3. Drainage: After forming, bubbles begin to drain due to the effect of gravity, they gradually shrink and burst.
  4. Disproportionation: In parallel with drainage, the reduced surface tension causes small bubbles to merge into larger, more unstable and fragile bubbles.
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In essence, crema is considered as a colloidal system with the dispersion of air bubbles in the continuous phase which is Espresso extract. More specifically, the gas phase consists mainly of CO2 produced during roasting and then retained in part in the cellular structure of the bean. The continuous phase is an emulsion system (consisting of oil and water) in which microscopic oil droplets (less than <10 nm, i.e. about 0.00001 mm) disperse in a coffee extract solution containing a number of components such as sugar, acids, proteins, etc. as well as small pieces of solid coffee cell (2-5 nm). Espresso Crema can be classified as super-durable foam with a fairly long life. In most cases, it can survive for 40 minutes before completely disappearing (the average for beer is 2 minutes). As the crema ages, its properties develop from the fine foam in the newly-prepared Espresso that becomes a polyhedral foam that dries as it ages. Ideally, crema should account for at least 10% of the volume of an Espresso with a foam density of 0.30 – 0.50 g/ml – according to The Craft and Science of Coffee. In crema formation, an energy source is required to create a dispersed system of air, fat in the liquid phase. For coffee, this form of energy comes from the pressure of an Espresso machine.
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In 1948, Achille Gaggia introduced a lever-operated, spring-loaded Espresso machine that pressed water through coffee under a pressure of about 9 bar. This is the first floor of oil and CO2 emulsified in an Espresso cup, which we now call the crema. Indeed, Gaggia has advertised this as an entirely new beverage, named Crema Caffe.  

Crema formation

There 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.
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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.  
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Factors affecting crema stability

After 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 & quality

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A 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 crema

Not 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?

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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.
  And after some more complex studies, we have clearly demonstrated that 4-vinylcatechol oligomers, rather than sucrose esters, play a major role in determining the structure of crema in a good Espresso. These results indicate that Robusta, which is richer in caffeic acid and chlorogenic acid than Arabica coffee, thus promotes the formation of 4-vinylcatechol surfactants during roasting, combined with pressure. and CO2 can explain the role of Robusta coffees foam boosting in Espresso better than Arabica. In summary, we have the basis for adding a quantity of Robusta coffee to Arabica when extracting Espresso, firstly Robusta with a higher acid content gives a better ability to form crema, secondly, Robusta has less oil. Therefore, the stability of crema is longer than that of Arabica coffee.
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How to produce a thick, delicious layer of crema

Refine coffee powder fineness

20-30 seconds is the standard extraction time for espresso coffee. This period also indicates that the fineness of your coffee powder is appropriate. However, for some reason but often because of the fineness that makes you extract coffee too quickly or too slowly – observing the flow will see it most clearly.
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In general, the espresso crema layer will be affected, as well. If the coffee powder is too rough, the water passes through the amount of flour in the basket too fast, before it can penetrate and extract all the substances in the cafe. In a nutshell, chemicals mean hot water has not yet been emulsified with coffee oil, and supersaturated with CO2 has been pushed out. Finally, you will get a bland espresso, sourness, and fragile crema. And if the coffee powder is too smooth, you can imagine it. Instead of the water passing through the coffee powder too quickly, it goes through extremely long and slow. Therefore, the result is that water dissolves too many substances in coffee than expected and make emulsification, supersaturation takes longer.
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The result is a bitter, rich aroma, dark brown Espresso Crema, and giant bubbles. In a nutshell, the first advice is to choose the right smoothness for Espresso. At the same time, the coffee powder must be uniformly smooth; the size between the coffee beans must be consistent.  

Control the source of water to make espresso.

Tap water and well water all contain an unexpected amount of minerals, odors, and flavors. While Espresso has a high requirement for water quality, if you use these two types of water to make Espresso, then a lot of bad things will happen to the machine. In the long term, the coffee machine is broken, and in a short time, the Espresso is not good.
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Some minerals such as ions, zinc, magnesium that permiss in water more than the permissible level will make the emulsification and supersaturation are hindered. In short, hard water is not suitable for coffee machines, not good for Espresso, and not ideal for the crema. So buy a water filter dedicated coffee machine for your machine as soon as possible.  

Use electronic scales every time you take coffee powder.

You can take the excess or lack of it and this situation starts to happen similar to the dough is too coarse or too smooth. If there is too much coffee powder in the basket, the water must be absorbed long and vice versa.
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So, adjust the number of grams of flour on your coffee grinder appropriately according to each type of coffee machine you currently own. If you use a commercially available coffee powder, be sure to equip yourself with an electronic scale when measuring each coffee powder into the handle.  

Clean coffeemaker periodically

The cleaning of the dispensing equipment is crucial, especially the coffee machine. During use, coffee oil and sediment will accumulate around the group-head, steam nozzles … that directly affects the flavor of Espresso and your espresso crema layer.
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Please clean your device after the end of each day and periodically follow the instructions of the technical staff. Especially clean the group-head, shower, handle cafe (handle), steam.

Choose the right type of coffee

Lipid is a water-insoluble substance, and it tends to separate from water, which affects the sustainability of espresso crema. Lipid content in Arabica is higher than Robusta. Specifically, in an espresso cup of 30ml contains about 46 – 146 mg of lipid for Arabica coffee and about 15 – 120 mg for Robusta coffee.
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Therefore, the coffee you use must have Robusta mixed with Arabica to be able to form a desired crema layer. Besides, the perfect level of roasting to have a nice crema layer is medium. Dark or light levels all affect crema formation.

The temperature and pressure of the coffee maker machine

If the pump pressure is weak (standard pressure is 9 bar on the professional machine; 15 bar on an automatic machine), it will not create conditions for hot water to emulsify the oils in coffee and then supersaturated with CO2. Besides, the temperature – including the blending temperature (92ºC) and the extraction temperature (70ºC) not reaching the prescribed threshold, also makes the crema fragile and rapidly dissolves. The tip for this is to use a thermometer to check before making coffee.  

Is your coffee new or too old?

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Degas is the process of releasing CO2 of coffee after roasting. It makes the state of coffee become perfect and sublime flavor after brewing. New coffee has not undergone degas and how much the old essence has evaporated. Ideally, buy high quality roasted whole-grain coffee. Mix a sufficient amount each time. Above is some basic information about crema, Espresso Crema as well as factors that can affect your crema layer. What about trying to make a Espresso Crema reward yourself after a hard-working day? Have fun and relax!  

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