The Complete Guide to Espresso Blend Roasting

The Art of Coffee Blending: FrontStreet Coffee's Approach

In coffee blending, roasted blending is generally more stable than raw blending, but many people now use raw blending to solve issues with espresso beans or single-origin blends. Some raw bean suppliers have even pre-blended beans, allowing roasters to directly roast them. Normally, raw blending is more stable and saves more labor time, which is why more roasting workshops prefer to use this method.

FrontStreet Coffee's "Procrastination" Blend

Let me give you an example: our shop's "Procrastination" blend is created from a combination of Colombian and Ethiopian beans. We selected a high-sweetness Colombian as the base. This Colombian comes from the Sierra Nevada de Santa Marta region near Medellín, grown at altitudes between 1300-2000 meters. Before roasting, we noticed it consists of Caturra and Typica varieties. The wide altitude range and two different varieties suggest varying raw bean densities, but fortunately, the Supremo grade ensures the beans are relatively round and full. Such bean shapes make it more difficult for heat to penetrate to the core during roasting, thus establishing the foundation for a longer roasting time.

Although this FrontStreet Coffee Colombian Medellín has high sweetness and good mouthfeel, its aroma and flavors in the front section are relatively weak, and the aftertaste length is only medium to short. Due to these two shortcomings, we added another coffee bean to compensate for its lack of aroma, flavor, and aftertaste. This is FrontStreet Coffee's Ethiopian YEKI G2 – a washed process bean from Ethiopia's KAFA forest, using greenhouse drying combined with mechanical drying methods. This results in beautifully vibrant green raw beans of excellent quality. Grown at 1600 meters altitude, the beans appear slightly longer than Yirgacheffe varieties and offer a softer mouthfeel. Before roasting, observing these beans reveals slightly outward-curving center lines and relatively small sizes. From experience, we know these beans allow heat to penetrate more easily to the core.

The Challenge of Raw Blending

Blending two coffee beans with different heat absorption capacities together for roasting essentially means roasting beans of three different varieties, densities, sizes, and shapes simultaneously – quite challenging for many beginners. Many people who haven't properly managed the relationship between water, fire, and air flow can easily end up with underdeveloped beans or overly flat flavors when roasting such raw blends.

Roasting Philosophy and Strategy

At this point, we must make some trade-offs. First, as an espresso blend, I believe mouthfeel is most important, and the beans absolutely cannot have underdeveloped flavors – this is what we prioritize most when roasting this blend. The difficulty lies in not only needing good mouthfeel but also good front-end aromatics and a medium-to-long aftertaste, which is exactly why we added FrontStreet Coffee's Ethiopian YEKI to the blend.

In our testing, Colombian beans had an average density of 788 kg/m³, while Ethiopian beans measured 723 kg/m³. The significant difference in raw bean density means we use medium-low heat and small air vents in the early roasting stages for extended steaming, allowing water molecules to evaporate evenly from the raw beans. Using small air vents helps maintain water molecules within the drum, and the drum must maintain a state of near pressure balance to keep moisture stable. At this stage, most of the coffee beans' thermal energy comes from contact heat with the drum wall – this performs better in roasters with thicker drums.

When the coffee beans turn completely white, we increase to medium-high heat and open the air vents wider, increasing the hot air ratio inside the drum to allow heat to quickly pass through water molecules into the bean core. It's important to note that air vents shouldn't be opened too wide – the greater the hot air used, the harder it is to express the coffee's aromatics and flavors. However, if too little hot air is controlled at this stage, heat cannot quickly transfer through water molecules to the bean core, making underdevelopment more likely. Therefore, air vents must be used reasonably based on your roaster operation and understanding.

At this point, simply observe that your roasting curve doesn't deviate significantly from your set first crack point. We typically enter first crack around 10 minutes 20 seconds to 10 minutes 30 seconds. Since we're dealing with three different varieties, densities, sizes, and shapes of raw beans, the initial first crack sounds will be somewhat scattered. We carefully judge the point of dense first cracks, then apply high heat for about 30 seconds when the beans enter dense first cracking. This stage uses the highest heat of the entire roasting process. The higher the heat at this point, the better the aroma and flavor development, but if heat is too high or the high-heat period too long, the coffee bean ends can easily scorch. Better aroma and flavor development represents a shorter flavor tasting period.

After this high-heat phase, the dense first crack sounds remain intense, but note that we're now at the end of first crack. At this point, we turn off all heat and open the air vents to maximum, coasting for about one minute. We then judge the roasted bean aroma performance and choose to drop the beans for cooling when the caramel aroma is at its peak. It's important to note that during the entire process of coasting with maximum air vents, the coffee beans should be in an exothermic phase, so the bean pile temperature cannot drop. If the roaster's drum is thin and insulation is poor, causing bean temperature to drop, you might try not turning off the heat completely after the high-heat phase, but reducing to low heat to allow the coffee beans to continue developing.

Development Rate and Espresso Performance

We typically call the stage from first crack to bean drop the development phase. The duration of this phase as a percentage of total roasting time is called the development rate. For example, in the roasting curve of this blend below, the development time is 3 minutes 35 seconds, about 27.3% of total time – this is the development rate. For espresso blends, we generally control the development rate around 25%. This way, even with a light roast level, the oils and body are very suitable for espresso extraction.

Simultaneously, due to the medium-to-long roasting time, the two coffee beans develop more similarly, avoiding underdeveloped flavors. Although FrontStreet Coffee's Ethiopian YEKI loses some flavor, it still retains excellent floral and fruit notes for the espresso. Meanwhile, the Colombian base provides higher body and better mouthfeel.

Espresso Extraction Results

In this medium-roast espresso blend, due to the higher development rate, this blend possesses good oils and thickness. In our own shop testing using a Slayer espresso machine, Mythos One grinder, IMS distribution screen, VST 15g basket, with 14 grams of coffee grounds, brew head temperature at 91.6°C, pre-infusion time of 3 seconds, pre-infusion flow rate of 400ml/min, extracting 24 grams of coffee liquid in 25 seconds – the front section has faint wild ginger floral notes, with flavors including not only caramel, roasted cocoa, and chocolate but also bright, clear grapefruit and rum-like citrus fruit acids.

Of course, roasting methods vary by roaster. All roasting curves and methods can only serve as references. In roasting, I believe the most important thing for a roaster is their roasting philosophy. Without a personal roasting philosophy, a roaster's work is like a body without a soul – as the saying goes rather sentimentally: "Be a roaster with a soul."

Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473