Fundamentals Part 2 – The Science

Fundamentals Part 2 – The Science

Fundamentals for “Reaching Espresso Nirvana” – for traditional, semi-automatic pump-driven espresso machines

Note: The following does not fully apply to super-automatic, hand lever, or steam power-generated espresso machines that may operate under different principles and guidelines for proper operation.

Part 2: The “Science”

In this section, we will cover the following areas that pertain to the “science” for Reaching Espresso Nirvana.

The Fresh Roast Of The Coffee Bean

“Estate Coffees”. Coffee beans from a single country are known as varietals. Blending, as preferred by roast masters, is the mixture of 2 or more “Estate Coffees” and/or varietals to produce their own signature coffee blend. Each Estate Coffee, Varietal, and Blend would change in flavor characteristics when the degree of roast changes. Just as wine changes flavor with age, coffee beans change in flavor with different roasting times.

According to roasting professionals, there are four (4) different types of roasts that are suitable for proper espresso extraction. In order of increasing darkness, they are Full City Roast, Vienna Roast, Espresso Roast, and French Roast. The main reason to utilize coffee beans with these roasts is that the flavor and crema production of espresso is highly dependent upon the oils formulated within the coffee beans during and after the roast. Any roast lighter than Full City Roast may not properly caramelize the coffee beans to produce enough oils for your espresso. As the roasts become darker, the oils tend to move to the surface of the coffee beans and you will see a “glossy” surface or feel the oils on them.

Another important factor in the roasted bean is freshness. Freshly roasted beans will provide superior tastes and aromatics. Stale beans or those laying around for a while will not allow you to achieve the fundamentals for Espresso Nirvana no matter how much you master the other variables.

Ultimately, it is important to experiment with different coffee beans (Estate Coffees, Varietals, and Blends) with a varying degree of roasts to find the one that best suits your palette! Most importantly, it is ideal to use coffee beans within 7 days of the roasting date!

The Fineness of The Coffee Grind

One of the most important parameters to proper espresso extraction is your coffee grind. The most important aspect of grind fineness is the ability to grind very, very fine (like NutraSweet) AND consistency. The consistency of the grind is directly attributable to the design and performance of your grinder. There are three types of grinders – hand grinders, blade grinders, and burr grinders.

Hand Grinders – Some, but not all hand grinders can grind fine and consistently enough for espresso extraction. The process of hand grinding involves the laborious task of turning the grinding handle many times. The advantage is that this slow process of grinding does NOT produce any heat that would negatively affect your coffee grind.

Blade Grinders – Blade grinders are identified by a whirling blade that “chops” the coffee beans. Grinding long enough, the coffee beans will result in a coarse grind more suitable for drip coffee. Grinding even longer, the coffee beans sometimes can turn slightly finer. However, the finest grind is not suitable for proper espresso extraction. The reasons are 1) The coffee grind will not be consistent, and 2) The high speed blade will create excess heat which will adversely affect the oils in the grind.

Burr Grinders – Burr grinders typically consist of two opposing grinding burrs – one stationary and one attached to the motor wheel. There are two types of burrs – conical and flat. Conical burrs are designed to produce greater consistency in the grind fineness. However, the type of burr becomes irrelevant as one chooses a high quality “flat” burr grinder that typically houses larger burrs closer to the commercial type.

Burr grinders typically have the advantage of lower heat generation due to the lower speed of the burrs. In addition, different degrees of fineness are achieved by changing the setting of the distance between the grinding burrs. The greater the distance between the grinding burrs, the coarser the grind. Oppositely true, the lesser the distance between the grinding burrs, the finer the grind. The equidistance of the grinding burrs achieves the consistency needed for proper extraction of espresso.

The settings on burr grinders will differ from customer to customer as all electric burr grinders have relative settings. This means that a setting of “6” on one particular grinder will not be precisely the same as a setting of “6” on another unit of the same model grinder.

Second, each type of coffee and the darkness of roast will require different settings to adhere to the fundamental rule. In the former instance, beans from two different farms, countries, or blends will have differences in the grind fineness from one to the other in acquiring the fundamental rule. The reason is that different beans have varying degrees of hardness. In the latter instance, a darker roast will require a coarser grind when compared to a medium roast to achieve similar extraction times and volume (however, the taste will be different). lighter roasted espresso beans should be ground finer than darker roasts. The main reason a finer grind is required on lighter roasts is that lighter roasted coffees do not have the oils on the bean surface. Therefore, a finer grind is needed to expose those oils on a greater surface area. Darker roasted coffees tend to have more oils at the surface.

Therefore, experimentation (not frustration) is essential in locating the best grinder setting for your coffee beans.

Finally, burr grinders should always be adjusted when the grinding burrs are in motion. This is especially important when adjusting from a coarse setting to a finer setting. The reason is that coffee grinds will always be between the two burrs, and this will not allow you to properly adjust the grinder to a finer setting. The end result is a more consistent grind and less chance of the burrs becoming dull or gummed.


The amount of coffee (known as the dosage) you place into the filter basket (on traditional filter handle machines) will also affect the “Fundamental Rule”. The industry standard in the United States is 7 grams of coffee roasted and ground for the single espresso shot and 14 Grams of coffee roasted and ground for the double espresso shot. This standard is an industry guideline. This means that the guideline can be adapted and changed to one’s personal need to achieve the crema rule and taste profile desired.

Typically, adding an amount greater than 7 grams of coffee will result in a longer extraction time since the extra coffee will increase the path the water needs to travel and creates greater resistance. Less than 7 grams would result in a quicker extraction time since there will be less coffee to create the resistance needed for proper extraction.

Wet Pucks: Wet pucks can result from too little coffee in the filter basket in combination with too fine a grind. When a wet puck is noticed, you may need to add more coffee to the basket and coarsen the grind. Please note the flavor profile may change as a result. If the best flavor profile is achieved with the result being a wet puck, then it is a good idea to leave things alone.

Tamp Pressure

Tamping is essential for proper espresso extraction. Tamping results in enough resistance for the water to pass through the grind, creating even distribution of pressure, and aids in allowing easy removal of the coffee from the basket after extraction.

Tamping is the application of force to compress the loose coffee grind in your filter basket into a “puck”. A special tool known as the “tamper” is utilized to press down on the coffee. A tamper is pre-built into some machines. In others, the back of the measuring spoon works as a tamper. More commonly though, a tamper must be purchased seperately.

The tamper consists of a tamping plate or “base” (made from plastic, wood, aluminum, or stainless steel), a stem, and a handle. There are two types of tamper bases – flat or curved. Flat tampers are typically used when the filter basket is straight on the bottom of the basket and curved tampers are used when the filter basket has a curved bottom. Neither type is universally superior to the other in terms of performance. Technique is more important than type for achieving a good tamp.

There are two types of home model espresso machines that impact the technique needed for proper tamping pressure. The first type are home model espresso machines that have PRESSURIZED handles or filter baskets. Please note that either the basket or the handle may be pressurized but never both on the same machine. This design compensates for tamping error by allowing the filter handle basket to create the pressure needed for proper extraction of espresso. Machines of this type include Capresso, Saeco, and the Solis Crema SL. Other machines, such as Gaggia, sometimes include pressurized disks that serve the same purpose. The second type are machines that have standard, non-pressurized filter handles or baskets. All traditional, commercial machines, as well as many home models, are of this type. Tamping pressure is much more critical on these machines since the resistance relies more on tamping pressure and grind fineness. This is due to the absence of added pressure from the design of the basket or handle. Below are the techniques for machines with pressurized and non-pressurized filters and baskets.

General Technique For PRESSURIZED Filter Handles and Baskets
The general technique for tamping in a pressurized filter handle or pressurized filter basket would be less than 30 pounds. In other words, only a very light tamp is needed. The proper tamp can be accomplished with the hand tamper, with the tamper built into the espresso machine or grinder, or with the back of the measuring spoon. please note that too firm of a tamp will not allow the water to come through the coffee grind or will result in a very long extraction time (usually exceeding 27 seconds).

General Technique For STANDARD Filter Handles and Baskets
The general technique for tamping in a standard filter handle is to apply about 30-50 pounds of evenly distributed pressure into the coffee ground dosed into the filter basket. The technique should be completed with a slight twist to result In a slightly polished finish on the surface of the tamped coffee. The 30 pounds of tamp pressure is a guideline and an area for experimentation as some of our customers have used less tamping pressure and others have tamped to 50 pounds of pressure. Some 1st-line Equipment customers have used a bathroom scale to measure tamp pressure. By using a scale to measure pressure, you can change one of the other parameters to achieve The Fundamental Rule.

Brewing Temperature

The optimal brewing temperature, as measured at the point where the water contacts the coffee grind, is 190-204°F. The temperature of the extracted espresso will vary from 150°F to 180°F. The temperature loss is attributable to the ambient temperature, the brew group temperature, and the temperature of the cup.

Therefore, it is important to preheat the brew group and the cup prior to extracting espresso The brew group can be pre-heated by pulling an “empty shot”. In other words, the filter handle and Basket should be placed on the brew group (or grouphead) without any coffee and hot water from the machine should be run through and into the cup that needs to be pre-heated. We have found a temperature loss of up to 100°F in circumstances where customers do not preheat the brew group, the filter handle, the filter basket, or the cup. Also, do not make the mistake of rinsing your filter handle and filter baskets with cold or hot faucet water. This can also reduce the temperature. It is best to wipe the handle and basket clean with a cloth or paper towel.

In addition, the closer the spouts of the filter handle to the base of the cup, the less the temperature loss due to room temperature.

Brewing Pressure

The optimal brewing pressure for a pump-driven espresso machine is 8 to 9 bar or atmospheres. Most machines show pressure “ratings” of Greater than 9 bar. Please note that these “ratings” indicate the “maximum” pressure that can be produced by the pump. It does not mean better espresso! Quite the contrary! Over 9 bar pressure can produce very BITTER tasting espresso.

Since most home model machines do NOT have gauges to monitor the brewing pressure, you may wonder how you know if we are at the optimal pressure. The answer is very simple. We will know if we are at the right pressure by comparing our results to The Fundamental Rule – Double Espresso Shot = 2 to 3.0 fluid ounces in 23 to 27 seconds.

The pump pressure is regulated by the resistance in the filter basket – The resistance of the espresso bean finely ground and tampered into the filter basket or the resistance created by the pressurized filter handle or basket.

A greater resistance in the filter basket will result in a greater pressure created by the pump. Too much pressure, the espresso will take longer than 27 seconds to extract. This is called over extraction and will result in a very bitter flavor. In addition, the home model espresso machines we sell have an expansion relief valve – when there is too much pressure (over 11-12 bar), this expansion relief valve will open to relieve the excess water pressure and divert it to either the machine’s drip tray or back to the water tank. The purpose is to avoid pump damage and lessen the chances of over extraction.

A lesser resistance in the filter basket will result in a lesser pressure created by the pump. Too little pressure, the espresso will take less than 23 seconds to extract. This is called under extraction and will result in a very weak, watered down coffee. In this case, the resistance in the coffee puck needs to be increased by changing one of the above variables – coffee grind fineness, amount of coffee grind, or tamping pressure. By grinding finer, increasing the amount of coffee grind, and/or increasing the tamping pressure, the resistance will become greater to extract at the right pressure.

Therefore, the resulting brewing pressure is a direct result of the resistance in the filter basket.

We have covered The Fundamental Rule and The Science. Now let us discover The Arte.

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