|Espresso shot with crema floating on top|
Stylish Glass Espresso Cup with Stainless Steel Handle
The beansSome beans will never produce crema, even some that are sold as espresso roast. The best espresso roasts use primarily Arabica beans, which originated in Ethiopia, but have spread throughout the coffee-growing world. Some Robusta beans are typically included in the blend because of their ability to generate crema. Most people imagine espresso roast beans to be dark, but it all depends on the roast. You can get both light and dark espresso roasts. The beans in an espresso light or mid-roast tend to be quite dry and shrunken when compared to dark roasts which are plump and oily. If you are buying your beans from a good source, they should be able to describe for you the crema-producing qualities of the beans. (My recommendation: Coffee Masters Ethiopian Yirgacheffe)
The grindIt seems everything has to be just so when making espresso and producing good crema. The next thing is the grind. Basically you are aiming at not allowing the water to pass through too quickly, but not making the grind so fine that your machine won't be able to force the water through without straining. This is achieved in two ways: the fineness of the grind of the beans, and the tamping of the beans in the portafilter. To achieve good crema, for a double shot, extract 2 to 2.5 ounces of coffee into your cup in 20 to 30 seconds from the moment you turn on the pump. You will see this referred to in various places as "The Golden Rule". (I have a completely different Golden Rule for perfect espresso you should read about.) A single shot should still take 20 to 30 seconds, but now you will want 1 to 1.5 ounces of coffee in your cup.
The flow of the coffee when being extracted should be steady and even, coming from both holes of the portafilter. If your coffee beans are ground too coarsely, the flow will be too fast and no crema will be produced.
On the other hand, if they are ground too finely, the flow will be too slow, or hardly any flow at all and your pump will be straining. To a certain extent, you can make up for the grind being too coarse by tamping the coffee harder, or if the grind is too fine, by tamping more gently. With a bit of trial and error, adjust your grinder setting until you achieve the correct flow and perfect crema production. You need to use a conical burr grinder that grinds the beans to an even consistency and which has multiple variable grind setting. Here is my recommendation for a conical burr grinder (Breville Smart Grinder).
TampingTamping is the process of pressing down on the ground coffee in the portafilter with a tool known as a tamper. The tamper should fit snuggly into the filter basket. Tamp with even pressure of about 30 lbs. How do you know what 30lbs is? Get out your scales and put them on the counter and practice so that you get the feel for how hard you need to press down. Tamping is aimed at achieving an even and consistent flow of the water through the coffee. If the coffee is packed unevenly, the water will find its way through gaps in the coffee, flowing too quickly through them for there to be a good extraction; most of the water will flow through the more loosely packed coffee, and not flowing through some of the coffee in the filter basket at all. In fact it is possible to bang out the coffee after the extraction is finished and see whole areas of coffee that are completely dry. You can't make good crema without tamping your coffee before the extraction.
Correct brewing temperatureThe temperature of the water has to be hot enough to caramelize the sugars in the coffee to make the crema. The optimal temperature range is around 92 to 96 degrees Celsius (198 - 205 Fahrenheit). The best machines use a metal for the boiler that has good heat retention, such as brass. Also, many machines offer separate boilers for coffee brewing and steam generation. This is because the water used for steaming has to be heated to a higher temperature than is the optimal temperature range for brewing the coffee.
Correct brewing pressureEffective brewing requires pressure of at least 130 psi, which some domestic machines just don't seem capable of. The pressure rating for your machine will be quoted in "bars". Many of the cheaper domestic machines achieve 8 bars of pressure, which is a stretch when it comes to achieving good crema. Get a machine that is rated about twice that. Sometimes these machines are described as "semi-commercial", but don't you believe it; consider this the minimum standard for your home espresso machine. (My recommendation: Breville BES900XL Dual Boiler Semi Automatic Espresso Machine or the Gaggia Evolution. See my reviews).
At the beginning, you will have to accept a certain amount of trial and error. Practice, practice, and practice some more. Vary everything: the grind, the amount of tamping pressure you use, and your beans.
With just a little bit of practice, provided you are using good fresh beans, you too will be pulling the perfect espresso shot with a rich layer of crema floating on top. Yum!