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  • Toxic elements of coffee roasting

    Why roast coffee?

    One of the most critical steps in coffee production is the roasting process. Roasting coffee beans has implications on coffee taste, smell and colour, and therefore has an overall affect upon the quality of the coffee. The length of roasting and the temperature that it is carried out and need to be optimized to produce the highest quality coffee possible from the bean. In addition to the coffee beans one of the major variables in the roosting process is the coffee roaster itself.

    Undesirable elements of roasted coffee

    In addition to the creation of wonderful tastes, colour, aroma and health gaining antioxidants, the roasting coffee beans process may lead to the creation of some undesirable chemicals that have a detrimental effect upon these elements and therefore if roasting is not carried out effectively it will have a marked impact upon the quality of the coffee.

    Chemical changes during coffee roasting

    One of the main chemical processes that occurs during the roasting of coffee is called the Maillard reaction, this affects free amino groups of peptides, amino acids and proteins, and leads to sugar becoming reduced when it is heated. This process leads to the creation of pyrroles, which give raise to the aroma of coffee. However as mentioned previously the roasting of coffee can also create unwanted elements; when carried out at 250 degrees, trigonelline, one of the components of raw coffee beans, is converted into compounds that are known to have mutagenic capabilities.

    Another component that has been identified in coffee is acrylamide, once again this is influenced by the Maillard reaction, and the length of roasting. The levels of acrylamide in coffee are lower in darkly roasted than in lightly roasted coffees. It is thought that the higher temperatures involved in creating a darker roasted coffee lead to the degradation or evaporation of acrylamides in the roasted coffee bean. A similar phenomenon is found with 5-hydroxymethyl-2-furfural, with it being created early in the roasting process and being degraded at later stages of roasting.

    Polycyclic aromatic hydrocarbons in coffee

    Other known toxins found in coffee are polycyclic aromatic hydrocarbons; it is thought that these may be found in coffee due to either their presence in raw green coffee beans or as a consequence of the roasting process itself. These polycyclic aromatic hydrocarbons are known to be both mutagens and carcinogenic in nature. It was therefore thought useful to find out which roasting conditions create different toxins in the diet. With this in mind Houessou and colleagues from Agro Paris Tech in france investigated the phenomenon further. Their findings are reported in the next section of this effect of roasting coffee article.


    Houessou et al (2007). Effect of roasting conditions on the polycyclic aromatic hydrocarbon content in ground Arabica coffee and coffee brew. J.Agric. Food Chem.
    Lantz et al (2006) Studies on acrylamide levels in roasting, storage and brewing of coffee. Mol. Nutr. Food Res. 50:1039–1046.
    Sharma and Hajaligol (2003). Effect of pyrolysis conditions on the formation of polycyclic aromatic hydrocarbons (PAHs) from polyphenolic compounds. J. Anal. Appl. Pyrolysis 66: 123–144.
    Yanagimoto et al (2002). Antioxidative activity of heterocyclic compounds found in coffee volatiles produced by Maillard reaction. J. Agric. Food Chem. 50: 5480–5484.