Why tasting is remains best method of testing tea quality

A tea basket on a tea farm in Tetu, Nyeri. [File, Standard]

Last year, when the tea bonus payment was announced, many smallholder tea farmers were not satisfied and believed that the payment ought to have been higher. I agree, the payment in many factories was not what we expected. In some factories, the prices were way lower than the monthly payment.

A debate on the price disparity between East and West of the Rift Valley came up, but I must say that this difference has been there for years. Teas from the east fetch a fairly higher price at the auction than those from the west. We should also note that even in the east some factories have a history of higher prices than others. 

Kagwe, Ngere, Gacharage, Kimunye, Kangaita, and Imenti are some of the tea factories known for high prices at the auction. Outside Kenya, some factories like Kitabi and Gisovu in Rwanda outperform others due to characteristics like the brightness of their infusions, briskness, and brightness of their cups, etc. The auction prices have a strong correlation with the final green leaf payment to the farmers.

Another debate arose over the quality determination of tea. Tea processing is managed through sticking to temperature ranges in withering, fermentation and drying, ensuring the crushing, tearing, and curling machines are well maintained. During processing, the tea is sampled. Tea tasters carry out quality evaluation using their senses. This is known as organoleptic testing, where tea is tasted by experienced cuppers who also, besides tasting, observe qualities like blackness, presence of fibres in the tea, creaming of the tea liquor as it gets cold, and others.

Critics of this method have challenged the industry to come up with more objective methods of quality determination. This is a good challenge. A commodity like milk has some characteristics, such as acidity, lactose content, and clotting on boiling, that can be determined using science. The sucrose percentage in sugar can also be determined scientifically. Such tests may also be used as a basis for the rate paid to the individual farmers.

Human senses

Tea, just like coffee, miraa, and tobacco, is a nutritionally challenged commodity (almost nutritionally useless) that is not taken for any nutritional value. These commodities possess organoleptic characteristics that make them so attractive to some human senses, thus causing addiction. 

Tea contains oxidation products, mainly flavour and colour compounds that are responsible for the flavour and the colour of the tea, respectively. If the characteristics attract the human senses, then the same senses are the best to determine the quality of the tea.

Some challenges are experienced during organoleptic quality determination. These include expectation error, where the taster has too much information about the tea he is tasting, causing bias due to what he expects. The ways the samples are arranged may also cause bias, as the tea cupper may think that tea liquoring cups are arranged starting from best to worst. 

Stimulus error happens when the taster is influenced by the colour of tea in the determination of the tea liquor quality, yet the two may not be related.

These errors can be mitigated through making the organoleptic testing more scientific through methods like developing tea cupping forms equivalent to the ones used by the Specialty Coffee Association, having more than one person do the cupping for comparison purposes. Ideally, blind cupping, where the tea samples are not labelled as per factory or origin.

Dr. Irungu offers specialist services in the tea and coffee industries