The Life Cycle of Coffee; Roasting

roasted coffee leaves the drum to the cooling tray!

For the intents and purposes of this article, roasting (and really everything in this series of articles) has been simplified, to say the least. Roasting can be approached as simple as pie or as complex as organic chemistry, quite literally. The aim here is to provide an overview of how we end up with roasted coffee.

As 50kg burlap bags bags of sweet smelling green beans arrive to be stored at the roasters location, the roaster is already planning how to alter every coffee to bring out its best. Roasting is the process of applying heat to coffee seeds to promote enzymatic browning, sugar caramelization, and pyrolisis; all crucial elements in developing a delicious roasted bean.

Roasting, it is said,  first occurred in a pan over hot coals, stirring the beans gently and quickly as they come up to temperature. Although this method is now only part of some traditional ceremonies and true aficionados, stove top roasters still exist. Given that only some sides of the beans are directly in contact with the pan, this style of roasting results in quite an uneven roast. As roasting has evolved, the objective has been to roast the entire charge of beans as evenly as possible.

There are 3 ways to apply heat to a coffee bean: Convection, conduction, and radiation. No roaster works on one of these alone, rather roasters have a combination of these features. Fluid-bed refers to any roaster in which the beans are roasted by a current of hot air which both roasts and agitates the beans. These range from dedicated coffee roasters to improvised pop corn poppers. Drum roasters offer the widest variety in method and controls and refer to a roaster in which the green beans are placed into a drum and heat is then applied to or through the drum. The method you use to roast coffee will significantly affect its final taste.

When the charge, or green coffee dose, is introduced into the roaster it immediately starts its transformation towards deliciousness. First the green beans begin to turn pale as they soften and release a smell much like that of freshly baked bread. As the roast progresses the beans turn pale orange and the smell becomes sweeter. When the beans become light brown, you begin to smell enzymatic browning and the smell of coffee is more pronounced. As this occurs, the roasting beans begin to “pop”, marking the beginning of First Crack. First crack is when beans expand in size and at this point coffee is roasted enough to be drank, but this is still considered a light roast. The popping then reduces and  more smoked is produced if the roast is continued. If you are  wondering why a roast would continue past the stage of drinkability then read on. After First Crack has concluded a second more subtle crack commences, Second Crack. Second crack marks the beginning of dark roasts.

Different roast levels give coffees different characteristics. Light roasts tend to accentuate brightness and acidity, nuance of origin (or the terroir of coffee), and noticeable body. Medium roasts, those in between the end of First crack and the beginning of Second crack, bring out more body and are the roasts most associated with the taste of coffee. Dark roasts accentuate the roast, not the origin. This isn’t to say, however, that the quality of green bean doesn’t affect a dark roast. Dark roasts have bold, smoky flavors are very pungent, but have little body or acidity. The time it takes for a charge of coffee to roast depends on the size of batch and the type of roaster. Fluid bed roasters for example are capable of creating great roasts at 5-6 minutes while some drum roasters can take up to 20. The roast however does not conclude at the time the roaster removes the charge from the roaster. The beans are still very hot (anywhere from 415-450 F) and need to be cooled immediately to prevent the roast to continue. To do this most roasters have a dumping tray with a fan underneath and rotating paddles that quickly cool the beans. Also there is a method of applying a fine mist of cold filtered water to roasted beans called quenching. Quenching the beans cools the roast quickly but must be closely monitored or the beans may become water logged.

As soon as coffee is roasted its momentum towards staleness is highly increased. Coffee flavors are mostly found in its naturally present oils. When coffee is roasted a large amount of CO2 is stored in the infrastructure of the bean. Its exerting force keeps oxygen away preventing it from staling the oils. As soon as that exerting force stops (after 2 weeks after roasting) oxygen seeps into the beans and quickly stales them. This is whole bean coffee we are talking about. As you can imagine, grinding coffee immediately releases all of its gas making ground coffee an extremely perishable product (about 2 hours of lifetime!) So it is important to always use fresh roasted coffee, and freshly ground coffee as well.

Large roasters, knowing that their coffee might be on the shelf for some time, use Nitrogen flushed bags to give their coffee some extra lifetime. As soon as coffee is roasted and cooled, it is bagged through a specialized machine that flushed Oxygen out by introducing Nitrogen. These bags also have a one-way valve, allowing nitrogen to escape but no Oxygen to come in. Most local roasters that don’t have this type of packaging, but rather brown paper bags, are meticulous to date roasts and restock old beans on their shelves. As you walk out of the store with your freshly purchased bag of coffee you get home and…

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3 Responses to “The Life Cycle of Coffee; Roasting”
  1. What do you mean by hot air agitating the bean?

    • lalinpv says:

      Good question Fabian,

      I should have specified. In fluid-bed roasting, a current of hot air blows into a chamber. The heat of the air is what roasts the beans, but the air current is what makes them spin, or agitates them. Also as beans heat up, them being in contact with each other also roasts them! Something true of all roasts methods. As I stated in the post, one of the methods of heat application is conduction; as the beans toss and turn, they touch each other, and conduct heat to each other.

      There are dedicated home convection roasters that agitate the beans by means of screws. Basically instead of flowing air through the chamber, the air in the chamber is heated to a certain temperature and a screw lifts the beans to the top of the chamber, they fall once they reach the top, and then commence the cycle again. This promotes even roasting.

      Let me know if this answers your question!


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