Want to systematically master the underlying logic of espresso? This article provides a complete overview of the core knowledge system of espresso, from equipment principles to practical details. First, it deeply analyzes the differences between four types of boiler heating systems and their impact on extraction stability, then explains steam wand selection, grinder burr structure, tamper matching principles, and key points for choosing latte art pitchers one by one. In the materials section, it focuses on comparing the roasting differences between Northern and Southern Italian style coffee beans and the logic for selecting suitable milk. Finally, it focuses on the five major extraction variables and six factors of milk frothing, and explains in detail the technique of integrating coffee and milk foam. The full text balances theoretical depth with operational guidance, suitable for coffee enthusiasts who want to solidify their foundation.
I found a great share in Group 4's space, so I'm posting it to the forum for everyone to share. The article comes from: Group 4: Hilton-Shijiazhuang
1. Professional Italian coffee machines
Based on the boiler's brewing and heating system, they are generally divided into four types: single boiler system, twin boiler system (also known as the sub-boiler or heat exchanger system), dual boiler system, and multi-boiler system. These four different boiler brewing and heating systems will create differences when we brew espresso. The main reasons for these differences come from the different boiler configurations and the heating methods of the heaters.
Single boiler system: In a single boiler system, the hot water, steam, and brew head water are all heated by the same heater. When using a single boiler system to brew coffee, the use of hot water and steam directly affects the brew head water temperature, causing instability. Therefore, single boiler systems are mostly used in home coffee machines or lever spring piston espresso machines. General commercial espresso machines no longer use this type of system.
Twin boiler system: In a twin boiler system, the hot water, steam, and brew head water are also heated by the same heater, but the twin boiler uses a heat exchange method with the main boiler for heating. When using a twin boiler system to brew coffee, the brew head water temperature is not directly affected significantly. Only when a large amount of hot water is used will the brew head water temperature drop. The twin boiler system is the boiler system used in most espresso machines on the market today, so as long as hot water is not used in large quantities, the machine's stability is within an acceptable range.
Dual boiler system: In a dual boiler system, the hot water and steam are heated by one heater, while the brew head water is heated by another heater. When using a dual boiler system to brew coffee, the brew head water temperature will not drop due to the use of steam and hot water, and the machine's stability is better.
Multi-boiler system: The heating method of a multi-boiler system is very similar to that of a dual boiler system, except that each brew head has its own independent heater and can be set to different water temperatures individually. Therefore, a dual brew head espresso machine has three boilers, and a triple brew head espresso machine has four boilers.
Each boiler system has its own characteristics and differences. When choosing an espresso machine, consider the following points:
a. Whether it is comfortable and smooth to operate
b. Whether all control buttons and knobs respond well
c. Whether the machine's stability is good
d. Whether the heating and recovery speed is good
e. Whether the steam output is sufficient
f. Whether the steam dryness is good
2. Steam wand, nozzle tip
Every espresso machine uses different steam wand forms and nozzle tip output methods. In terms of steam wand form, they are divided into long tube type and short tube type, and among these, there are also thick tube type and thin tube type. When using a long tube steam wand, due to its length, the steam strength is somewhat weaker than the short tube type, but the long tube type is less restricted during operation; the thick tube steam wand has a larger steam output and weaker strength, while the thin tube type has a smaller output and stronger strength.
The output method of the nozzle tip is greatly related to the arrangement and position of the steam holes. Most steam hole configurations are 4-hole and 5-hole. Different arrangements cause different steam directions, so they are categorized into the outward horizontal spread type and the concentrated type.
Different forms of steam wands produce differences in steam strength and output. Combined with differences in steam hole positions and number of holes, this creates differences in the angle and method when steaming milk. Before using an espresso machine, pay attention to what type of steam wand is being used, and then pair it with appropriate milk frothing. Only then can you produce dense and fine milk foam.
3. Choosing a grinder
Most professional grinders on the market use flat burr grinding to grind coffee beans, while most home grinders mainly use blade type, using a chopping method to grind coffee beans. The uniformity of the coffee grounds after grinding differs greatly between the two. Although flat burr grinders are more expensive, they have a great impact on controlling coffee brewing. Therefore, it is still recommended to choose a flat burr grinder as the first choice.
Professional flat burr grinders can be divided by blade type into flat burrs and conical burrs. Most use flat burrs, which consist of upper and lower burr discs. The lower burr disc is driven by a motor to rotate, achieving the grinding of coffee beans. The upper burr disc is rotated to adjust the spacing between the upper and lower burrs to control the coarseness of the coffee grounds. Common flat burr sizes have diameters of 58mm, 64mm, 75mm, and 84mm. Larger diameter burrs not only grind faster but also produce more uniform grounds and generate less heat, better ensuring that the aromatic compounds in the coffee grounds do not dissipate excessively. In addition, pay attention to the adjustment increment of the upper burr when rotating the setting; it should not be too large, so that finer adjustments of coffee ground coarseness can be made. Also, some grinders add a counterweight to prevent vibration during grinding from causing uneven coffee grounds. Therefore, we can choose a good professional grinder based on the above points, which has a very critical impact on professional coffee quality.
4. Coffee tamper
There are many different types of coffee tampers on the market, but broadly speaking they are mainly divided into flat type and convex (rounded) type. As for differences in material and weight, these vary according to individual habits and techniques, so we will not discuss them further here. So how should one choose between a flat type and a convex type tamper? Before choosing, first pay attention to the brew head screen of the espresso machine and the shape of the filter basket on the portafilter. A flat screen and filter basket should be paired with a flat type coffee tamper, and a convex screen and filter basket should be paired with a convex type coffee tamper. Only then can the tamped coffee puck, after absorbing water and expanding, evenly seal with the screen and filter, allowing even extraction of the coffee puck. Otherwise, it will cause uneven density after the coffee puck absorbs water and expands, resulting in over-extraction or under-extraction during brewing. Therefore, choosing an appropriate coffee tamper is very important.
5. Latte art pitcher
There are also many types of latte art pitchers. Based on the spout shape, they are mainly divided into pointed spout type and round spout type. The pointed spout pitcher makes it easier to draw fine-line circles, while the round spout type is smoother when drawing symmetrical patterns. Based on the groove form of the pitcher spout, they are divided into long groove type and short groove type. The longer the groove shape, the better the milk gathering effect and the easier it is to control when drawing patterns; while the shorter groove is easier to use when skimming milk foam. In addition, the handle form is also divided into connected type and separated type. The connected type pitcher handle is easier to grip, while the separated type pitcher is easier to use when chilling and cooling. As for which pitcher is better to use? Actually, as long as you are skilled and accustomed to it, that is enough, so more practice is the key to success.
Other tools include thermometer, stainless steel spoon, hand-pump milk frother, stainless steel pot, stainless steel cup, espresso pot, electric stove or gas stove, toothpicks, needle-like objects, sieve, etc.
Materials that determine quality
1. Espresso coffee beans
There are many types of espresso coffee beans on the market. Because espresso beans express rich and multi-layered flavors and mouthfeel, they are all blended using a combination of beans. Espresso is also divided into Southern Italian style and Northern Italian style coffee. Northern Italian beans use a medium-light roast. Due to bean selection, the caffeine content is lower, and when sipped, the flavor is rich and bright with a slight fruity acidity, and the aroma leans toward floral or fruit peel notes; Southern Italian coffee beans use a dark roast. Because of the bean blending method, the caffeine is higher, and when sipped, the flavor is intense with a caramel-like sweet finish, and the aroma leans toward fruit or cocoa notes.
Why is there such a difference between Northern and Southern Italy? Because Italy is a long, narrow country, the climate difference between north and south is quite large. Residents in the north, because the climate is colder, have relatively lighter dietary tastes, so the coffee bean roasting method is mostly medium-light roast; while residents in the south, because the climate is hot, have heavier dietary tastes, so naturally the coffee bean roasting leans toward dark roast. Also, because of the wealth gap between north and south, people in Northern Italy tend to use a higher proportion of Arabica beans when blending coffee, so the caffeine content is lower, and relatively the coffee oil content is also lower; while people in Southern Italy add Robusta beans when blending, making the caffeine content higher than Northern Italian style, so the coffee oil content is also richer.
2. Milk
Generally speaking, whole milk is more suitable when choosing milk, and milk with a milk fat content above 3% is even more suitable. Different brands differ slightly in taste, texture, and composition. When choosing, match according to personal preference and coffee beans. If the espresso beans chosen are Southern Italian style, then when choosing milk you can select one with a richer milky aroma. However, if you want to particularly emphasize the coffee's flavor, you can also choose milk with a moderate milky aroma. If the espresso beans chosen are Northern Italian style, then when choosing milk you can select one with a medium milky aroma, so that the coffee's flavor will not be overwhelmed by the milk. But if you want to particularly emphasize the milk's aroma, you can also choose milk with a rich milky aroma. It all depends on your own needs and preferences.
3. Other materials include cocoa powder, cinnamon powder, chocolate sauce, caramel sauce, etc.
Coffee cups and latte art
The shape of the coffee cup is also greatly related to the latte art method. Generally speaking, cup body shapes are divided into two major categories: tall cups and short cups. Tall cups have a longer body, and the force is also greater. However, if the amount of milk foam is insufficient, when starting to draw the latte art pattern, there will not be enough milk foam to create a beautiful latte art pattern. Conversely, if the amount of milk foam is abundant, the resulting latte art mouthfeel will be excellent, but the technical difficulty is relatively higher. Because short cups have less capacity and shallower depth, the movements during latte art must be very quick, and it is more difficult when making advanced and highly difficult patterns. However, short cups make it easier to present latte art patterns when brewing coffee.
In addition, the shape of the cup bottom is also very important. It is broadly divided into round bottom and square bottom. Round bottom cups have better blending uniformity than square bottom cups. The reason is that square bottom cups have a larger bottom surface area, which lowers the height of the espresso, so during blending it is more prone to excessive rolling, causing the surface cream to break. Moreover, the right-angle shape of the square bottom also makes the rolling motion during blending less smooth, and blending is also prone to unevenness, resulting in a less uniform taste when drinking. Also, the diameter of the cup rim will produce different effects. The larger the cup rim diameter, the larger and brighter the latte art pattern that can be made, but because a larger diameter means a larger surface area, the thickness of the milk foam will be affected and reduced. However, if the cup rim diameter is too small, the difficulty of latte art increases.
Finally, when choosing a cup, select one with good heat retention so that the coffee's temperature can be maintained.
Key factors for successful latte art
Coffee——adjustment and settings of machine equipment
1. Professional Italian coffee machines
A. Boiler pressure
Boiler pressure gauge: The unit displayed on the boiler pressure gauge is bar, which is the unit of atmospheric pressure. It is generally adjusted to 1±0.2bar. Some boiler pressure gauges and inlet pressure gauges are displayed within the same pressure gauge, configured either top-bottom or left-right. The easiest way to identify the boiler pressure gauge is that its measurement scale is smaller, and the needle changes little when brewing coffee.
Boiler pressure adjustment box: Most espresso machines have the same boiler pressure adjustment box. Only a small number of brands use their own manufactured parts for adjustment, or use computer board settings. So now we will introduce the general method. The boiler pressure adjustment box has two adjustment screws: one is a locking screw, and one is an adjustment screw. When adjusting, first loosen the locking screw, then turn the adjustment screw to adjust. In most cases, the adjustment direction is clockwise to reduce pressure and counterclockwise to increase pressure. After adjusting to the set pressure value, tighten the locking screw.
B. Brewing pressure
Brewing pressure gauge: The display unit of the brewing pressure gauge is also bar, generally adjusted to 9±2bar. Before brewing coffee, the pressure value shown on the brewing pressure gauge is the water pressure of the inlet line itself, generally around 1-2bar. After pressing the brew switch, it will display the set pressure. There is also one thing to pay special attention to: when setting the brewing pressure, you need to fill the portafilter with coffee grounds, because only then is the brewing pressure setting value correct. This is because the pressure when coffee grounds are loaded will be greater than when no coffee grounds are loaded, so pay special attention to this point.
Brewing pressure adjustment screw: The brewing pressure screw is located at the water inlet pump. Most of the time, some parts of the espresso machine's casing need to be removed, though some espresso machines are designed with the brewing pressure adjustment screw in a more accessible position. When adjusting the brewing pressure adjustment screw, first loosen the rear locking screw, then turn the front adjustment screw. In most cases, the adjustment direction is also clockwise to reduce pressure and counterclockwise to increase pressure. After adjusting to the set pressure value, tighten the locking screw. However, some espresso machines have a brewing pressure adjustment screw that turns in the opposite direction.
2. Commercial grinders
When adjusting the coarseness of coffee grounds on a grinder, simply rotate the setting dial. In most cases, rotating the adjustment setting clockwise makes the coffee grounds coarser, and rotating counterclockwise makes the coffee grounds finer. Commercial grinder setting dials are divided into two types: one type has fixed locking pins on the setting dial, and adjustments are made one notch at a time. The increment per notch varies by brand. Generally speaking, the smaller the adjustment increment, the better, because then finer coarseness adjustments can be made; the other type has no fixed locking pins, and you simply turn the dial directly when adjusting. Also note that after adjusting the setting dial, you should grind some coffee beans and discharge the coffee grounds from the grinder's grounds chamber, so that the coffee beans ground afterward are at the set coarseness.
The 5 major brewing factors of espresso
The scientific definition of espresso is: coffee grounds dose——6.5±0.5 grams; brewing water temperature——90±5℃; brewing water pressure——9±2bar; brewing time——30±5 seconds. When brewing espresso, we must use the scientific definition as the baseline. However, because there are too many factors to pay attention to when brewing a cup of espresso, with about twenty different influencing factors in total, we will not discuss them here.
Brewing pressure: The greater the brewing pressure, the higher the proportion of coffee chemical substances extracted. But what percentage should be extracted to be correct? This must be determined according to the condition of the coffee beans used and daily changes. There is no so-called absolute standard brewing pressure value, but we can use the scientific definition of espresso as a basis to adjust to the correct brewing pressure setting.
The boiler pressure value, assuming the same atmospheric pressure value, will produce different brew head water temperatures due to differences in each boiler's volume and water level setting. Therefore, the correct brew head water temperature must be determined through measurement. When the boiler pressure is lower and the temperature is lower, the extracted coffee will have more obvious acidity and the overall flavor will be weaker; when the boiler pressure is higher and the temperature is higher, the extracted coffee will have a heavier burnt flavor and the overall flavor will be heavier. Therefore, we can use this principle as a basis for adjusting the extracted coffee's flavor.
Coffee ground coarseness: Basically, the three control factors of "coffee grounds dose, tamping force, and coffee ground coarseness" are used in coordination with one another to tamp out different coffee puck densities and thereby adjust and control the degree of coffee extraction. As for coffee ground coarseness, in most cases the coarser the coffee ground particles, the shallower the extraction, the more acidic chemical substances and the fewer bitter chemical substances; conversely, the finer the coffee ground particles, the deeper the extraction, the more bitterness and the less acidity. However, some coffee beans will differ from the above principle due to the characteristics of the bean variety itself. Everyone should pay attention!!!
Coffee grounds dose: The greater the coffee grounds dose, the more the coffee concentration and body will increase. Assuming the same coffee puck volume, when the coffee grounds dose is too much, the density of the coffee puck will be too compact, causing under-extraction of the coffee grounds; when the coffee grounds dose is too little, the density of the coffee puck will be too loose, causing over-extraction of the coffee grounds. Therefore, only an appropriate coffee grounds dose can correctly extract the chemical substances in the coffee puck.
Tamping force: The force used to tamp coffee grounds is determined by the coarseness of the coffee grounds and the amount of coffee grounds. Assuming the same coffee ground coarseness and dose, if the tamping force is too great, the density of the coffee puck will be too compact, the water passage and extraction time will be lengthened, resulting in over-extraction; when the tamping force is too small, the density of the coffee puck will be too loose, causing under-extraction.
The state of the coffee extract: After brewing coffee, you must observe the state of the coffee extract to check whether the correct coffee extract has been obtained according to your own settings. This is because the state of the extract will differ according to the coffee bean blend, roast level, espresso machine adjustment settings, and the barista's brewing technique. It is not, as is commonly said, that only coffee extract with reddish-brown cream is correct. Take Northern Italian style medium-light roasted coffee beans as an example: the surface cream is not reddish-brown. Therefore, when the cream's texture is even, the body is sufficient, and there is no over-extraction or under-extraction color, that is the ideal state of the coffee extract.
The principles and methods of milk frothing
a. Why use frothed milk?
The basic principle of milk frothing is to use steam to strike the milk, causing liquid milk to incorporate air. By using the surface tension of milk proteins, many tiny bubbles are formed, causing the liquid milk to expand in volume and become foamy milk foam. During the frothing process, lactose dissolves into the milk as the temperature rises, and the frothing action seals the lactose within the milk foam. The function of milk fat is to allow these tiny bubbles to form a stable state, so that when these milk foams are consumed, the tiny bubbles burst in the mouth, allowing the flavor and aromatic substances to disperse and amplify better, giving the milk a sweet, rich taste and mouthfeel. Moreover, when blending with coffee, the bonding force between molecules is stronger, allowing the characteristics of both coffee and milk to stand out individually while also blending completely together, achieving a mutually complementary effect.
b. Making dense and fine milk foam
There are many different ways to create a good milk foam texture, but they all include two stages: the first stage is aeration, which means injecting steam to cause the milk to foam and increase in volume; the second stage is texturing, which means using a vortex method to fold air into the frothed milk, causing larger milk foam bubbles to burst and break down into fine bubbles, and allowing the milk molecules to bond, making the milk foam texture denser.
There are many milk frothing methods on the market, but they are broadly divided into two major categories: one is aeration and texturing at the same time, which combines the milk aeration and milk foam texturing stages; the other is separating the aeration and texturing stages, meaning first aerating the milk and then texturing the milk foam. These two methods produce different milk foam textures and mouthfeels. The first method, aerating and texturing at the same time, produces a finer and softer milk foam texture, but the milk foam's thickness will be thinner, and it is less easy to produce a dense, elastic milk foam texture, though the round shape for latte art is easier to form; the second method, first aerating the milk and then texturing the milk foam, produces a milk foam texture with higher thickness and can create bouncy, elastic milk foam, but it is more likely to produce coarser milk foam texture during the aeration stage, making latte art patterns more difficult to create, though the resulting latte art mouthfeel will be denser.
6 factors affecting milk foam
a. Milk temperature: Milk temperature is a very important factor when frothing milk. For every 2℃ rise in milk storage temperature, the shelf life is reduced by half. Also, the higher the temperature, the more milk fat breaks down, and the lower the frothing degree. When milk is being frothed, the lower the starting temperature, the more complete and uniform the protein denaturation, and the higher the frothing degree. In addition, note that the optimal milk storage temperature is about 4℃.
b. Milk fat: Generally speaking, the higher the milk fat content, the denser the milk foam texture, but the proportion of milk foam will be less. Therefore, if all high-milk-fat whole milk is used, the resulting milk foam texture is not necessarily in the best state. By appropriately adding some already-frothed cold milk, the resulting milk foam texture and amount will be greater and denser.
c. Steam wand form: The steam wand output method is mainly divided into outward horizontal spread type and concentrated type. Different forms of steam wands produce different steam strength and output, and combined with changes in steam hole position and number, this causes differences in angle and method when frothing milk. When frothing milk with an outward-spreading steam wand, it should not be too close to the edge of the pitcher, so as to avoid turbulence; with a concentrated steam wand, more attention must be paid to angle control
d. Steam volume: The greater the steam volume, the faster the milk is frothed, but relatively speaking, coarser milk foam is more likely to be produced. The method with a large steam volume is also more suitable for use with a larger stainless steel pitcher; too small a pitcher tends to cause turbulence. A steam wand with a smaller steam volume has a poorer milk foaming effect, but the advantage is that it is not prone to producing large bubbles, and although the time needed to froth and texturize is longer, overall control is easier.
e. Steam dryness: The higher the dryness of the steam, the lower the water content, and the milk foam produced will be finer and denser with less water content, so the better the dryness of the steam, the better.
f. The size and shape of the latte art pitcher: The size of the pitcher is related to the type of coffee drink to be brewed. The larger the drink volume, the larger the pitcher needed. Generally speaking, when making cappuccino, use a 600ml pitcher, and when brewing latte, use a 1000ml pitcher. Only by using the correct pitcher capacity can well-structured milk foam be produced. Since this is a method of making latte art, the shapes of the pitchers are mainly sharp-spout types, and for pitchers with different sharp-spout shapes, you will need to practice a lot on your own.
The principles and methods of integrating coffee and milk foam
The principle of integration: The integration of coffee and milk is a very important step when brewing espresso. It can raise the taste and mouthfeel of espresso to a better level, and it can also correct small errors that occur during the making of espresso and milk foaming. Through the methods and techniques used during integration, it can also change the strength and lightness of the mouthfeel of the entire cup of coffee. What is the principle of integration? First, let us use our imagination to picture coffee, milk, and milk foam as individual molecules. The best way to integrate is for the entire cup of coffee to be a uniformly combined body of coffee, milk, and milk foam molecules. To achieve such a state, it is necessary during integration to provide the force that binds the molecules together, and this force must be stable and continuous. Therefore, during integration, milk and milk foam molecules should be poured in a measured way so that the coffee, milk, and milk foam molecules form a uniformly combined body. This allows every sip of the entire espresso to be a uniformly combined body of coffee, milk, and milk foam molecules, so that the effect of each molecule can be brought into play and the entire cup of coffee can present its best state.
One of the integration methods,
1. During the integration action for coffee, first bring the pitcher close to the rim of the cup and do not pour too much milk foam, so as to avoid the initial impact force being too great and breaking up the cream on the surface.
2. Then raise the pitcher and add a larger amount of milk foam to increase the force of integration.
3. Then lower the height of the pitcher and control the flow of milk foam so that the integration force is even.
4. Then raise the pitcher again to perform the second integration action.
5. Finally, lower the pitcher to near the rim of the cup, and after the cup is full, quickly cut off the milk foam.
Integration techniques: Before integrating the coffee and milk foam, we must use a stainless steel spoon to scrape off the coarser milk foam from the surface layer of the foamed milk. Special attention must be paid to the way the spoon is held: the fingers should be placed against the back of the spoon to avoid scooping up the delicate milk foam that was so painstakingly created.
During the integration of coffee and milk foam, the most important technique is to maintain a certain flow of milk foam to integrate with the coffee and to provide an appropriate integration force. When we pour in the milk foam, the pitcher must continuously move up and down to provide integration force, but a certain amount of milk foam must still be maintained in the pour. Therefore, when the pitcher rises, the amount of milk foam must be increased, so the wrist must control and increase the amount of milk foam being poured. When the pitcher descends, the amount of milk foam must be reduced, so the wrist must control and reduce the amount of milk foam being poured. During the process, milk foam must still be poured continuously rather than intermittently, so the elbow should be raised slowly at a constant speed. This technique must be practiced continuously in order to be used proficiently. We can use the size of the milk foam flow when pouring and the size of the impact force during integration to change the strength and mouthfeel of the coffee when drunk. The greater the integration impact force and flow, the lighter the coffee mouthfeel when drunk; the smaller the integration impact force and flow, the stronger the coffee mouthfeel when drunk. In this way, different strengths of mouthfeel can be adjusted to meet the needs of different customers.
The speed and rhythm of integration: There is another very important factor during integration, namely the speed and rhythm when integrating the coffee and milk foam. The speed of integration affects the strength and lightness of the coffee when drunk, while the rhythm affects the overall performance of a cup of coffee and the presentation of the pattern during latte art. Be fast when it should be fast, and slow when it should be slow. The grasp of rhythm requires proficient skill and accumulated experience, and different latte art patterns will have different rhythms.
The above content is compiled by CoffeeHunters, a coffee news website.
