The selection and extraction of raw materials for the production process of instant tea

1. Raw Material

The raw materials for instant tea extraction are now divided into two types: dry tea leaves and fresh leaves. The content level, composition ratio, and fineness of quality components in tea raw materials are the main factors affecting the processing quality and yield of instant tea.

To improve the quality and yield of instant tea, before processing：

On the one hand, it is necessary to carry out appropriate preprocessing such as chopping and screening of tea raw materials, in order to extract more and faster quality components of the raw materials without blocking the pipeline or causing difficulties in the filtration process; another

On the one hand, it is necessary to blend tea products from different origins, seasons, varieties, flavors, and even tea types to improve the quality and stability of instant tea.

Generally speaking, the selection of raw materials for instant tea processing is based on cost reduction, with a focus on evaluating the color, aroma, taste, and water extract of the raw materials, rather than paying too much attention to the external specifications of the raw materials. Therefore, the processing materials for instant tea have strict requirements for internal quality and relatively loose requirements for appearance. Usually, middle and low-end tea materials (sliced tea, crushed tea, ground tea) and by-products such as tea stems are mixed and processed with regular tea in a certain proportion. At the same time, in order to improve the efficiency of filtration and clarification, it is advisable to control the particle size of the raw materials used for instant tea processing between 8-24 mesh

2. extraction process

Extraction is a fundamental and important process step in the processing of instant tea, and the extraction conditions and efficiency directly affect the yield and quality level of instant tea. The extraction process conforms to the principle of “similar solubility”, which essentially involves dissolving soluble substances from the raw material through a solvent (usually pure water or deionized water).

The factors that affect extraction efficiency and product quality mainly include extraction method, solid-liquid ratio, temperature, time, frequency, etc. The extraction method mainly depends on the extraction equipment, which can be divided into intermittent, semi continuous, and continuous types according to their operation mode; According to the processing methods of solid raw materials, they can be divided into fixed bed, moving bed, and dispersed contact type; According to the contact mode between solvent and solid raw materials, it can be divided into multi-stage contact type and differential contact type.

(1) Continuous extraction

When the processing capacity is large, continuous extraction is generally used. In order to avoid the movement of tea leaves during extraction, several fixed beds can be used to continuously extract the extraction solution. At present, there have been many research reports and production applications on extraction technologies such as ultrasound assisted extraction, microwave-assisted extraction, and enzyme assisted extraction. However, in industrial production, currently deionized water or purified water is mainly used as solvents, and continuous countercurrent extraction or fixed bed extraction tanks are used for extraction.

(2) Continuous countercurrent extraction

Continuous countercurrent extraction, also known as continuous dynamic countercurrent extraction, refers to the process in which the material and solvent move continuously in opposite directions during the extraction process. The material constantly changes its contact with the solvent during the movement, effectively improving the extraction state and significantly enhancing the extraction efficiency. Continuous quantitative feeding through mechanical transmission mechanism; The material moves continuously during the extraction process. Without disrupting the feeding sequence, the material is slowly kneaded to ensure full contact with the solvent during the extraction process, ultimately resulting in continuous slag discharge. At the same time, the solvent is continuously updated inside the equipment, and the effective components of the material are continuously obtained during the flow process, resulting in a continuous increase in concentration. In the process of continuous liquid inlet and outlet, there is a continuous concentration gradient in the solvent, which enables the extraction solution to achieve a relatively fast leaching rate and a relatively high extraction solution concentration

Different tea raw materials require different temperatures and times for continuous countercurrent extraction. The solubility requirements of the product are different, and the temperature and time for continuous countercurrent extraction are also different. Cold soluble instant tea requires low extraction temperature and short time. For conventional hot soluble instant tea, the extraction temperature for stir fried green tea and steamed green tea is 60-80 ℃, and the extraction time is also 60-70 min; The extraction temperature of black tea is 70-90 ℃, and the extraction time is 70-80 min; Fragrant oolong tea and roasted oolong tea are extracted at a temperature of 80-95 ℃ and for 70-80 minutes. In continuous countercurrent extraction, the tea to water ratio is generally controlled at around 1:20.

(3) Dynamic extraction tank extraction

When using a dynamic extraction tank for extraction, boiling deionized water or purified water (90~95 ℃) is usually used. The extraction is carried out in two stages with a tea to water ratio of 1:8 and 1:7, and each cycle is refluxed for dynamic extraction for about 30 minutes. Under this method, the extraction index of water extract in tea raw materials is 0.8~0.9.
Microwave assisted extraction has the advantages of simplicity, economy, and time-saving, and has been applied in many fields. Similarly, when applied to instant tea extraction, high-quality products can be obtained.

(4) Microwave extraction

The main factors affecting the microwave extraction process are microwave heating power, type and concentration of extractant, and operating technology. By optimizing the extraction conditions, good extraction results can be achieved, and the microwave extraction temperature is generally below 75 ℃. Compared with conventional water extraction, microwave-assisted extraction shows that the former is superior to the latter in terms of yield, quality, and efficacy of instant tea quality components. The microwave method is used to prepare instant tea powder from tea powder, which has the advantages of short process time, high yield, and easy industrial production. The optimal conditions for microwave extraction are a power of around 640W, a time of 120-150s, a material to liquid ratio of 1:15, and two extractions, resulting in a high yield of instant tea.

5. Ultrasonic extraction

Ultrasonic extraction technology utilizes the special physical properties of ultrasound, such as strong longitudinal vibration, high-speed impact crushing, cavitation effect, stirring, and heating, to destroy the cell structure of the extract, allowing the solution to penetrate into the interior of the cells, thereby accelerating the dissolution of effective tea ingredients and improving the extraction rate of effective ingredients. When using ultrasound assisted extraction, ultrasound is a sound wave with a frequency greater than 20kHz, characterized by high frequency, short wavelength, and strong penetration.

Research has shown that ultrasonic extraction can greatly shorten the extraction time of instant tea, improve extraction efficiency, and rarely change the structure of active ingredients, which to some extent solves the problems of low aroma, weak taste, and low yield of instant tea products. When using ultrasonic assisted extraction to extract high-end green tea, not only is the extraction rate higher than conventional extraction techniques, but the extract also has a bright yellow color, fresh taste, and long-lasting fragrance.