Correlation Chemical Sensory Evaluation Develop Higher Quality Tea Biology Essay

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The principle of living in vitality requires consumption of food products of good quality. Amongst the food categories beverages form a major group of the food industry. The beverage industry in South Africa is vast and amongst the beverages hot tea is steadily growing in popularity. Hot tea contributes 5% of the total value € 500 billion (non-alcoholic; excluding milk, tap and packaging bulk water) of the beverages worldwide (Unilever, 2009). Tea in the commercial sense would refer to a blend of individual grades/types of refined tea leaves sourced from different tea estates. These are combined according to specifications (determined by the food company) to yield a product with an expected taste, colour, aroma etc.

In accordance to one's responsibility as a food technologist, providing food products including tea that is of good nutritional and sensory quality is the goal. The quality attributes of tea would be described in terms of taste (including flavour and strength); colour/hue, aroma and mouth feel of the brewed tea.

However, maintaining standards of good quality is not always sustainable as conditions of sourcing and processing are susceptible to change due to corporate factors. Thus the drive for continuous improvement. In particular Unilever's share of the world black tea being over 20% (Unilever, 2009) has been in recent months receiving consumer complaints (with noticeable increase) of a popular branded black teabag ( for purpose of this study will be referred to as Brand B) in terms of non-conforming taste. With further Pareto analysis, this found that the consumer complained of weak tasting tea.

Therefore the research to be conducted entitled "The correlation of chemical and sensory analysis inured to develop a high quality tea product" will be for the purpose to isolate the major factor specifically between the porosity of the filter paper used versus the dosage of tea that could possibly influence the strength of Brand B tea.

The process will involve preparation of samples of Brand B tea packaged in two other types of filter paper (for the purpose of investigating the influence of filter paper porosity) as well as samples of the same tea in varying weights packaged in the current filter paper used for the brand. These samples will then be tested against each other with analysis of their soluble solid yield, the polyphenol content and the scoring received during sensory analysis by experts of the company.

The overall goal in the commercial sense will be to implement actions, stemming from the study that would inhibit the factor that most impacts on decreasing the strength of the tea. Thus the consumer complaints will decrease resulting in the company achieving one of its targets for the year. In addition if the results show that a decrease in dosage of tea will increase the strength to a consumer satisfactory level then the company will be saving a noticeable amount of money on raw tea. Obviously the opposite could take place if this would be untrue. On the other hand if porosity of filter paper results in being the major defecting factor then the action to change the type of filter paper used could lead to cost savings or extra expenditure of approximately R8781750 (Unilever, 2008) on filter paper.

1.1 Basics on Tea

Tea comes from the botanical bush Camellia Sinensis a white flowered evergreen indigenous to the rain forests of Asam, Northern Burma & South West China but has since been cultivated across the world including South Africa. The tea bush is an extremely hardy & sturdy bush that adapts well to different climates. With the economic life-span of 100 years it yields 40g of black tea per year. . (Bernard & Hajkoop, 1997)

The quality of tea depends on the tea producing area, the area of the plantation it grows in, different times of planting, different planters, variety of seeds and clones. These factors determine the final flavour, thickness & colour of tea.

The manufacturing process which converts the young fresh leaves into tea was developed by the Chinese in ancient times. However now differences in fermentation produces three main kinds of tea.

Unfermented green tea, which is steamed or pan dried

Semi-fermented Oolong tea or red tea

Fully fermented black tea

Manufacture of black tea involves five phases i.e. withering, rolling or cutting, fermenting, drying and grading.

Withering- It involves spreading the leaves over a bed which is 22cm deep and forcing circulation of air with the use of fans. The process takes 12-24 hours. The purpose is to reduce moisture, with moisture loss of 20 to 45%. Withering makes the leaf soft and flaccid and facilitates cutting. It induces various biochemical changes which aid fermentation, such as increasing polyphenol oxidase and enzyme activity, facilitating cell wall permeability, controlling the caffeine level, freeing amino acids and increasing aroma development.

Cutting (CTC) - Cutting, tearing and curling involves passing the withered leaves through pairs of stainless steel mangle-like rollers, etched with sharp-edged intermeshing helicoidal grooves. These shred the leaves into small pieces. This process serves to rupture and open cells of the bud, stem and leave tissue to squeeze out and mix the cell content and juices.

Fermenting- Here the shredded leaves are left to ferment, no biological agents are added. Tea fermentation is essentially the conversion of a simple substrate occurring within the cells of the young shoots into more complex substances under the influence of natural enzymes. A noticeable colour change takes place as the shredded green leaves change to a brown colour.

Drying- Drying aims to stop fermentation at the optimum point of colour, taste and aroma development. It also produces a dry stable product. Fluid bed dryers are used to dry tea, where the tea enters at a temperature of 100°C and exits with a moisture content of 2 to 3%, yielding 400 kilos of tea per hour.

Grading- The dried tea leaves are sorted into a number of grades of uniform particle size using vibrating sieves. At the same time, pieces of stalk & fibre are removed to present a cleaner product.

These graded teas are received by the site to package as teabags.Unilever packs over 100 000 tonnes or 30% of its tea volume in teabags, primarily for black and flavoured tea. The teas are packaged on equipment which are supplied by three manufactures namely, Teepack, IMA & MAISA (Bernard & Hajkoop, 1997), the PMB site uses equipment supplied from IMA, who manufacture a range of Heat-seal machines.

1.2Black Tea Grading

Broken black tea is classified into four different categories i.e. whole leaf, broken leaf, fannings and dust (FML, 2001). An example of whole leaf would be FOP or flowery orange pekoe which consists of fine, tender, young leaves rolled with a certain proportion of "tips". These tips, being the very end of the buds leaves, constitute a guarantee of quality.

Fannings black tea is made from smaller, flat pieces of broken orange pekoe and used to make quick-brewing, flavoured, robust teas with good colour. Dust black tea consists of tiny bits of broken leaf used to brew strong tea quickly, popular for black teabags.

1.3 Why do we blend?

Blending tea ensures that consumers are given a consistent quality and taste from a variable raw tea material, in the required volumes and the lowest possible price. A blend is a combination of different types of tea to maintain the flavour consistency. Due to the large variations in tea flavours from single estates (changing from day to day), teas have to be blended to achieve a consistent flavour and colour through the year. Twenty or more original teas can make up one blend.

1.4 CTC and Orthodox

CTC and Orthodox are process through which the complex series of chemical changes known as oxidation are initiated. The processes are both effective and produce teas with differing characteristics. Orthodox processing involves the tea leaves rolled slowly using traditional rolling tables that mimic the action of hand rolling. This disruption of the leaf cells causes slow oxidation. The process takes approximately four hours. The result is rolled leaves, larger in size and requiring a longer brewing time in order to obtain all the flavour and colour. Generally the tea is light and clear red in colour, preferred by those who like loose tea. (Unilever, 2009)

CTC stands for cut, tear and curl. The tea leaves are passed through a series of cylindrical rollers with small sharp teeth that cut, tear and curl the leaves. The process gives the intense colour and small tea leave size that teabag brewing requires, due to a rapid oxidation process (approximately 90 min). The finished product brews quickly, gives a rapid rich red colour delivery and has a higher level of soluble solids on leaf surface.

Table 1 Average chemical composition of Orthodox and CTC black teas from Assam (FML, 2001)


Orthodox teas

CTC teas

Water soluble solids %



Theaflavins %



Thearubigin %



Total lipid



Flavour volatilised



The table above presents the relevant bio-chemicals that black tea contains, as will be mentioned later on, certain chemicals listed (polyphenols) above are responsible for the strength of the tea therefore the quantity of these chemicals present determine the brewing strength of the tea. Commercially CTC tea is used to produce teabags and this is appropriately so as the tables shows that CTC teas contain more polyphenols which is needed to compensate for the filter paper porosity that may hinder the infusion of the tea thus leading to a weaker brew.

1.5 Composition of black tea

Depending on plant cultivar, climate, soil and cultivation practices, Potter and Hotchkiss (1995) stated there are about 1500 slightly different kinds of tea leaves; these can further be modified in processing and contribute to differences in the final brew and provide opportunity for custom blending to according to commercial brands.

Tea is comprised of three main components i.e. caffeine, polyphenols and essential oils (also called aromatic or volatile oils). It must be noted that additional elements are introduced during tea processing. Polyphenols sometimes incorrectly referred to as "tannins" are responsible for the colour, briskness, flavour and strength of teas, often associated with the terms body and astringency. They account for one third of the soluble material in leaves, but differ in type between teas. Groups of related polyphenolic compounds are called catechins. In black teas, through fermentation, the catechins have formed into larger, more complex structures called theaflavin and thearubigins, which provide complex flavour and colour.

Essential oils contribute significantly to the fragrance of tea and somewhat to its taste. They accumulate in the leaf as it grows, evaporate during and after manufacture. Exposed to strong heat, they will disappear completely, which is why they are also referred to as 'volatile' oils.

Unilever 2009 states caffeine stimulates the central nervous system, promotes blood circulation and stimulates the kidneys to produce more urine. All types of tea contain 40mgs of caffeine per serving, depending upon blend and strength of brew.

Table 2 Principal components of black tea (FML, 2001)


Concentration (g/100g)









Phenolic acids and Depsides


Amino acids








Mineral matters




Components measured in wt % of extract solids.

1.6 Principle of Soluble Solids effecting strength of tea

As stated by the table above black tea used for producing teabags have a noticeable amount of polyphenols present in the final product. Since polyphenols are the principle components that give rise to the taste (strength and astringency) of the tea, the research shows that logically the larger the amount of polyphenols present in the tea the stronger the taste it will yield. (Roberts and Smith, 1963-cited by Liang et al., 2002) Other studies also showed that theaflavin content is an important chemical compound determining the quality if black tea.

1.7 Properties of Filter Paper

Filter paper for teabags is composed of food grade approved oxygen-bleached or unbleached wood pulps and a range of man-made fibres and chemicals with co-polymers to provide a sealable layer for heat sealable filter paper.

An ideal type of filter paper used for teabags would prevent fine dust particles of tea from filtering through the teabag, which at the same time has the capacity for allowing air or gas within the bag to readily escape so that the bag would readily sink to the bottom of the cup rather than float on top of the liquid when the teabag is being used. The filter paper should also have the wet strength necessary for a teabag and that is adequately porous so that the water will readily flow through the teabag for infusion purposes. With these properties in mind, in order to make a desirable cup of tea, the air and gas should be discharged from the teabag during infusion, for the presence of air or gas in the bag will cause it to float on the water in the cup instead of settling to the bottom. The occurrence of this would hinder the brew of a strong cup of tea.

1.8 Sensory Quality of Tea-Relevant History

Research has show that there has always been a link between soluble solid content (SSC) and the sensory attributes of tea as consumers and professionals perceive it. However most studies have been conducted on tea samples sourced from different estates and not on a brand of teabags that consumers will actually experience. Li et al. (2007) states that SSC is one of the major characteristics indicating the quality of black tea and to measure SSC they used analysis based on the Vis/NIR spectroscopy.

However, Liang et al. (2002) proved that there was significant correlation between the individual quality attributes of tea when comparing results from the chemical composition and colour difference of tea (through HPLC) to the sensory evaluation by tea tasters.

In comparison to the methods to be employed for this study, the principle is the same i.e. the aqueous extraction system however in industry the method is more conventional and less time consuming. In terms of sensory analysis the taste panel is the most common method used in industry and the scientific community although Tudu et al. (2009) had successfully attempted to employ the electric nose for the evaluation of the aroma of tea.

2. Aim

To develop a higher quality tea product by determining the most causative factor between the porosity of the filter paper versus the dosage of tea in a teabag of Brand B that result in a weak tasting tea through the aqueous extraction of soluble solids, quantifying the polyphenol content and sensory analysis of brewed tea.

To determine the correlation between chemical and sensory analysis conducted on a higher quality tea product.

3. Objectives

To extract and quantify the soluble solid content of tea samples packaged in different types of filter and at varying weights through an aqueous extraction system.

To evaluate the quality of tea samples of varying weights and packaged in different types of filter paper by sensory analysis of brewed tea.

To determine the polyphenol content of tea packaging at varying weights and different filter paper.

To determine by statistical methods the most causative factor i.e. the filter paper or varying tea dosage the yields weak tasting tea.

4. Materials and Methods

4.1. Preparation of Samples

4.1.1. Porosity Testing-Samples

2.5g of Brand B tea will be sealed in 0.5g of filter paper. This will be done by folding and stapling close, the filter paper which will also be attached to 20cm tag-string to assist in the dunking process. Two types of filter paper (g and a) will be used, 8 samples will be prepared using each filter paper. The control will be a sample of Brand B teabag weighing 2.5g packaged in the current filter paper used for the brand.

4.1.2. Dosage testing-Samples

Three different dosage (weighted) samples will be prepared using the filter paper of Brand B. Four samples each of tea weighing 2.0g and 3.0g will be sealed and attached to a 20cm tag-string by folding and stapling together. The control will be teabags of Brand B which weighs 2.5g, this being the current standard.

4.2. Aqueous extraction of Soluble Solids

Each type of sample prepared above will be used to extract the soluble solid content.

Day 1

The oven will be pre-set to 103°C as well as the water-bath will be filled and switched on. Kettles will be filled with water until water boils (100 °C). The metal trays will then be labelled, weighed & recorded. The prepared samples will be weighed and recorded. The teas will be transferred into beakers, the timer set at 3min, the tea will be liquored with 250ml of hot water, brewed for 3min. 50ml of tea will be transferred to metal trays which will be placed onto water baths to dry until excess liquid has evaporated. Then the trays will be placed in the oven at 103 °C for 16hrs. (Unilever, 2005)

Day 2

The trays will then be removed from the oven & then placed into a dessicator

for 15min, the trays will then be weighed and recorded. The percentage of soluble solids will then be calculated using the following:

% soluble solids = wgt of residue x 5 X 100

Wgt of actual tea

(Unilever, 2005)

4.3 Sensory Analysis (Unilever Bestfoods, 2003)

4.3.1 Tea Batch preparation

Appropriate tea tasting crockery (cup with lids and bowls) will be organised 5.6g of tea i.e. two teabags will be placed into the cup. The timer will be set at 3 minutes. Simultaneously de-ionised boiled (100°C) water of will be poured into the cups at a quantity of 250ml and 5ml of milk to be added with the lids to cover. After the 3 minutes the covered cups will be tipped over to drain the tea into the bowls. There after the tasters will slurp the liquid with a spoon to the back of the mouth to evaluate the sensory attributes.

4.3.2 Scoring attributes

The taster will evaluate the tea by sight (colour), smell (aroma) and taste (flavour and strength). Each attribute will be scored using points from 0.2 (worst) to 8(excellent).

4.4 Statistical Analysis

Each evaluation conducted will be allocated a percentage which will be used to give each sample a final score. Percentage allocations will be Sensory evaluation-50%; soluble solid content-20% and Polyphenol content-30%.

4.5 Polyphenolic content- HPLC

Sample preparation

Each sample prepared as 4.1, will be brewed in a cylinder using 125ml (de-ionised) water at 100°C. Aliquots as per the HPLC conditions will be consumed from this brew.

HPLC conditions

The polyphenols will be analysed using a Shimadzu LC-10 AD HPLC system fitted with a steinless steel column, length 25cm and diameter 4.6mm at ambient temperature. The injected volume will be 20µl. The mobile phase will be acetonitrile:methanol (75:25, vol/vol) with a flow rate of 1ml/min at a run time of 5 min. The polyphenols will be determined using a Shimadzu SPD-6AV UV-Vis detector with wavelength of 294 nm. The peak area will be measured using the Shimadzu C R5A recorder.

5. Work plan



Research Topic


Formulate Research question


On going search and collection of literature


Formulate aims and objective


Write up proposal for project


Prepare and present project proposal

March 4th

Develop/organise method and material for experiment

March -Apr

Execute experiment and correlate results


Write up project dissertation


Present project and findings