Course:FNH200/Projects/2020/The Processing and Roasting of Coffee
Coffee:
Coffee is known for having stimulating effects.[1] To gain more insight into what goes into making coffee, additional information on topics such as processing methods, roasting, the chemical reactions and other possible uses of coffee beans has been provided below. Furthermore, an in-depth look at caramelization, Maillard reaction, dry processing, wet processing and semi processing is focused.
Processing methods
Dry processing:
This process is favoured in areas where water resources are limited and where the climate can support drying the fruits in the sun.[2][3] Freshly picked coffee cherries of all maturation stages are dried whole in the sun over a period of a few weeks until a moisture content of 11% is reached. [2][3] After the fruits are dried, the fruits are cleaned and husked to remove all the other parts of the fruit excluding the beans.[2]
Wet processing:
In this method only mature fruits are used; the coffee cherries are pulped to remove the flesh and skin of the fruit from the beans.[2] Once pulping is completed, the beans are fermented in tanks filled with water for up to 48 hours to remove any remaining flesh as well as the mucilaginous residues attached to the parchment.[2][3]
The beans are then washed and dried, also to a moisture content of 11%, before removing the remaining outside layers on the bean, the parchment and testa (seed coat), in a process called hulling.[2][3]
Semi-dry processing:
This method begins similarly to wet processing in which the cherries are picked and pulped; however the mucilage is left on and not fermented.[4][5] Instead the beans are left to dry with the mucilage on for approximately two hours or until the moisture level is 30-35%.[4][6] Then the beans are hulled so the parchment is removed, before undergoing a second drying process until the moisture content of 12-13% is reached, at which the beans attain a dark green colour.[5][6]
Once the beans have been husked or hulled depending on the processing method, they are optionally polished and sorted before their storage and exportation.[3]
Roasting
Chemical Reactions:
The major difference between coffee roasts comes from the chemical reactions that occur in the coffee beans at certain temperatures. As a result of these chemical reactions, aromatics, acids and other flavor components are created, balanced or altered in a way to build a variation of flavors, acidities, and aftertastes.
1. Maillard Reaction
The Maillard reaction is a main factor in the development of flavour and colour in roasted coffee. The reaction is a form of non-enzymatic browning which typically proceeds rapidly from around 140 to 165 °C. Heat causes a reaction between the carbohydrates and amino acids (the building blocks of proteins) in the beans. This causes changes in color, flavor, and nutritional content.
The carbohydrate level in the coffee bean plays a key role in the Maillard reaction. Quakers (unripe coffee beans) are a great demonstration of this – the lack of sugar means that Maillard and caramelisation reactions cannot take place, and the resulting beans are pale and lacking in flavour. As well as flavour, melanoidins formed in the Maillard reactions also play an important role in forming and stabilising crema in espresso, and provide body to brewed coffee. They may also provide some of coffee’s health benefits – especially antioxidant and anti-inflammatory activity (AS Moreira et al, 2012). [7]
The length of time spent in the Maillard reaction is also an important factor in viscosity and flavour. Coffee that has spent longer in the Maillard reaction has been reported to have an increase in viscosity. A shorter Maillard duration can create more perception of sweetness and acidity. This is in part because the acids that produce fruity and sweet notes are destroyed if the coffee remains in the Maillard reaction for too long.
2. Caramelization
Caramelization is the browning of sugar, a process used extensively in cooking for the resulting nutty flavor and brown color. Like the Maillard reaction, caramelization is a type of non-enzymatic browning. However, unlike the Maillard reaction, caramelization is pyrolysis (thermal decomposition of materials at elevated temperatures), as opposed to reaction with amino acids.
From 170-200°C the sugars in coffee start caramelizing, which browns the sugar and releases aromatic and acidic compounds. As the process occurs, volatile chemicals are released, producing the characteristic caramel flavor. In our roasting, we find that the length of the caramelization phase most closely correlates to the coffee’s expression of body and sweetness. In general, the faster a coffee proceeds through caramelization phase, the more it will tend to express a lighter body and higher sweetness; the slower a coffee proceeds through caramelization the more it tends to express higher body and lower sweetness.
Roast Levels
Light roast:
Light roast coffee beans have a light brown colour and contain no surface oils. They also have more flavour than the medium and dark roasts, but also contain the most caffeine. These beans have a “toasted grain” taste with a noticeable acidity taste. During the roasting process, the first crack (when the bean cracks and expands) occurs between 300- and 350-degrees Fahrenheit. When we refer to coffee as a “light roast,” it essentially means the coffee has only been roasted up until the “first crack”.[9]
Medium Roast:
Like the name suggests, medium roasted beans are a bit darker in terms of colour, compared to the light roast beans. However, similar to the light beans, medium roast beans have no oil on their surface. Medium roasted beans are roasted between 410- and 428-degrees Fahrenheit. This temperature is just before the second crack occurs.[9]
Medium-Dark roast:
Lokker explains how medium-dark roasts have a darker brown colour, and heavy body with a very little amount of oil on the surface of the bean. These beans are roasted at 437-450 degrees Fahrenheit. These beans tend to have a slight spicy taste to them.[9]
Dark Roast:
Like dark chocolate, these dark roasted beans have a very dark brown colour to them. Dark roast beans have a thin body and burnt/charcoal taste due to the temperature these beans have been roasted at. To get dark roasted beans, they are roasted at 465-480 degrees Fahrenheit. This temperature is at the end of the second crack, sometimes even past the second crack threshold. Dark roast beans contain less caffeine than the other beans.[9]
Additional Uses
Coffee is very versatile and aside from roasting it for a drink, there are many other ways to get a caffeine buzz from coffee. Coffee can be added as a flavour enhancer to multiple food items such as ice cream, tiramisu and even on steak. In addition, the advancement of technology has allowed for the creation of zero waste coffee products. Items that can be made out of coffee waste include, cascara, which is a tea that can be made out of the dried skin of coffee cherries. Coffee can even be made into a sparkling coffee called ŝelosoda from the dried discarded coffee cherries. Coffee can also be made into flour and be used as an insect repellent and air freshener. The leftover grounds from coffee can be composted and used as a fertilizer for a garden.[11]
Potential Exam Question
In coffee roasting, with increasing duration of the Maillard reaction ________:
- A. The flavour does not change
- B. The sweetness decreases
- C. The acidity decreases
- D. Both B and C
Correct answer: D
This question reviews a concept we learned in Lesson 2, and demonstrates the implications of roasting duration on the flavour of coffee.
References
- ↑ George, Sunitha Elizabeth; Ramalakshmi, Kulathooran; Rao, Lingamalli Jagan Mohan (May 2, 2008). "A Perception on Health Benefits of Coffee". Critical Reviews in Food Science and Nutrition. 48 (5): 464–486. doi:10.1080/10408390701522445 – via Taylor & Francis Online.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Kleinwachter, Maik; Bytof, Gerhard; Selmar, Dirk (2015). "Coffee Beans and Processing". Coffee in Health and Disease Prevention: 73–81 – via Elsevier ScienceDirect.
- ↑ 3.0 3.1 3.2 3.3 3.4 "10 Steps from Seed to Cup". National Coffee Association USA. Retrieved August 4, 2020.
- ↑ 4.0 4.1 "Coffee Processing Methods". Cartel Coffee Roasters. Retrieved August 9, 2020.
- ↑ 5.0 5.1 "Semi-washed processed coffee". Trabocca. Retrieved August 9, 2020.
- ↑ 6.0 6.1 "The Semi-washed/Wet-hulled Process". North Star Coffee Roasters. Retrieved August 9, 2020.
- ↑ Moreira, Ana S. P.; Nunes, Fernando M.; Domingues, M. Rosario; Coimbra, Manuel A. (April 13, 2012). "Coffee melanoidins: structures, mechanisms of formation and potential health impacts". Food & Function (3): 903–915. doi:10.1039/C2FO30048F – via Royal Society of Chemistry.
- ↑ Sheth, Sarang (May 9, 2018). "Roast Levels". Yanko Design. Retrieved August 11, 2020.
- ↑ 9.0 9.1 9.2 9.3 Lokker, Brian (December 11, 2017). "Coffee Roasts from Light to Dark". Pinebrook Roasters. Retrieved August 10, 2020.
- ↑ Jansen, Maureen (April 18, 2014). "Coffee Flour Product". Sprudge. Retrieved August 11, 2020.
- ↑ McCusker, S (November 24, 2015). "Zero Waste Coffee: 5 Creative Uses for Coffee By-Products". Perfect Daily Grind. Retrieved August 10, 2020.
External Links for further exploration and research
[1] Chemical Changes in the Components of Coffee Beans during Roasting
[2] Handbook of Coffee Processing By-Products: Sustainable Applications
[3] Following Coffee Production from Cherries to Cup: Microbiological and Metabolomic Analysis of Wet Processing of Coffea arabica
[4] How Much Caffeine in Coffee Cup? Effects of Processing Operations, Extraction Methods and Variables
[5] How Can We Minimize Waste in the Coffee Industry?