|Apparatus for preliminarily desiccating tea-leaves in medium and small enterprises (00:00:00 Ngày 16/02/2006)|
Using inappropriate apparatus for preliminarily desiccating tealeaves could decrease the quality of commercial black tea, leading to loss of foreign currency in the tea export. The following paper includes recommendations on necessary technical parameters for enterprises could produce by themselves apparatus for preliminarily desiccating tealeaves abiding by standards. Consequently, there is presentation of apparatuses suitable to medium and small enterprises for tea processing.
Preliminarily desiccating tealeaves is the first step in the process of black tea production, but it is an important step with a decisive role on technological subsequent process and on quality of the final product. Technically fit preliminarily desiccating tea not only creates the homogeneity of bud pliability, but also retains most tannin, solvent substances as well as increases activation of polyphenoloxydaza enzyme, creating favourable conditions for the subsequent process of crumpling, fermenting to generate characteristics of products, thus preventing phenomena of breaking, pulverizing, staling…
State of ineffective apparatuses for preliminarily desiccating tealeaves.
In some recent years, along with the renovation of national economy, the tea processing branch, mostly black tea processing for export, had substantial changes. The quantity and capacity of tea processing in small and medium enterprises had been increased at a rather accelerated pace. But the remaining problems are: due to spontaneous development in the pursuit of immediate profits, the processing equipment, particularly apparatus for preliminarily desiccating tea leaves in these small and medium enterprises in yet rudimentary, so the production efficiency is not satisfactory , with high energy cost and low product quality. The price of Vietnamese exported tea is rather low as compared with other countries’ product. Average price of Vietnamese tea in world markets fluctuates with in the range of USD 900 ÷ 1,100 / ton whilst the average price from other countries is USD 1,400 ÷ 1,800 / ton.
Surveys on medium and small enterprises’ apparatuses for preliminarily desiccating tea leaves in Yen Bai, Thai Nguyen and Phu Tho provinces had shown that all these enterprises are using trough for tea leaves’ preliminary desiccation. This technology although being labour intensive, not mechanized, automatised in production, is very appropriate to production scope and investment capacity of these enterprises. Noteworthy, all troughs for tea leaves’ preliminary desiccation are designed, manufactured at random, without any scientific basis. The proportion between length, width and height of troughs being irrational, makes it difficult to the operation of workers, with low productivity. The height from trough bottom to wired mesh for supporting tea leaves is usually low and uniform from beginning to end, the temperature of hot air being high (up to 42°C and over), thus affecting the gradual desiccation, and at the end of desiccation process, many tea buds are still green and some tealeaves are over dried … the proportion of conveniently desiccated tea leaves being low.
Improved technology and equipment
Starting from the above production facts, the research team led by Dr. Do Van Chuong had put forth ideas for studying the basio parameters of tea desiccating trough as fundamentals for designing, manufacturing such trough. The concept of it is that: the design and manufacture of the desiccating trough is not merely based on specific conditions of each enterprise, but foremost on the air flow of ventilator as a principal parameter. By practical experience combined with refenence on relevant domestic and foreign documents, the research team had proved that the most adequate air flow supplied to tea leaves desiccating is about 1,000 cu.m/hour for each square meter of trough bottom. The slope of trough is about 1/100 for creating uniform pressure of hot air flow on the tea layer from end to end of trough.
The ratio between the width of trough (R) and the diameter of ventilator being 1,8 for creating a thickness of desiccated tea layer of about 25 cm and convenient to operation of workers.
Enterprises could base on these parameters to design and manufacture apparatuses for preliminarily desiccating tea leaves according to their specific conditions.
Without half way stopping, expert of the research team had made surveys on equipment in the market for providing processing enterprises with necessary information on axial ventilators generally used in tea leaves’ desiccation. Those are Vietnam made ventilators as well as Indian ones now existing in our market. Information on these ventilators is shown in (Table I).
One step forward, for convenience in the application process, the research team had made use of its achievement to design a series of desiccating troughs for processing enterprises to rely on it in selecting equipement appropriate to their condition. (Table 2).
For controlling and demonstrating research results, the team had manufactured and installed a type of trough with dimensions: 22 m long, 1,8 m wide (bold italics in Table 2) at the Hoai Trung tea enterprise (Chi Chu hamlet, Chi Tien commune, Thanh Ba district, Phu Tho province). Experiments shown that the difference of temperature between lower and upper layers of tea being about 1°C. This difference of temperature as well as that of hot air flow above and under the tea layer is almost constant from end to end, proving the homogeneity of tea mass during the process of desiccation. Experimental results also shown that when using these types of desiccation troughs at hot air flow of 35 ÷ 38°C, the duration of desiccation being 6 ÷ 8 hours, the quality of semi - products shall be highest. The rate of properly desiccated tea reached 80 ÷ 86,3%, the desiccated tea being supple, of dark - greenish colour. Meanwhile, with the use of previous troughs, the above rate was only 70%, and desiccated tea leaves being not so uniform, with greenish - yellowish colour.
It is safe to say that, with their effort, the research team having designed, manufactured such an efficient apparatus, not only had provided medium and small tea processing enterprises with scientific bases for designing various types of troughs, but also provided them with many necessary information on technology and equipment of this important processing stage. That is a substantial act helping enterprises reduce production expenditures and creating conditions for improvement of quality and prestige of Vietnamese black tea in the world market.
Enterprises in need of information on design, manufacture of tea processing trough could directly contact with: Dr. Do Van Chuong, Research Team Leader, Tel: 0912.237.567 or Department for processing agricultural, forestry produces and Salt, Ministry of Agriculture and Rural Development 2 Ngoc Ha, Ba Dinh, Ha Noi, Tel: 04 7.335785.
Some types of appropriate tea desiccating troughs for medium and small tea processing enterprises
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