Cooling, filtration, and clarification in the production process of instant tea

cooling

Cooling is an important process in the extraction of instant tea that affects the quality of the product. After the extraction of tea raw materials, the solid content in the extraction solution is usually 2% to 3%. Due to the fact that the extraction solution is a multi-component liquid system based on water-soluble substances in tea leaves, substances such as tea polyphenols are sensitive to heat and easily oxidize and polymerize to form some large molecular substances or turbid precipitates, which can seriously affect the biological activity and cold solubility of the product.

Therefore, it is necessary to use a heat exchange system (such as a refrigerator) to cool the extraction liquid to a suitable temperature to prevent the oxidation and polymerization of heat sensitive components in tea leaves, which may form substances that are not conducive to quality. Generally, instant tea is divided into hot soluble and cold soluble types. If it is a hot soluble product, the temperature of the extracted liquid after cooling should be below 20 ℃. If it is a cold soluble product, the temperature of the extracted liquid after cooling should be below 4 ℃. Therefore, the lower the temperature of the cooling water used in large-scale production, the better the cooling speed and effect. When producing cold soluble instant tea, it is best to use frozen water below 0-4 ℃ as the cooling water.

Filtering and clarification

The purpose of filtration and clarification is to remove fine particles, suspended impurities, or turbid precipitates formed during the processing of the extract. The degree of clarity and transparency directly affects the quality indicators such as color and cold solubility of instant tea products.

At present, the main filtration and clarification methods used in instant tea processing include centrifugal settling filtration, disc centrifugal separation, high-speed tube centrifugal separation, and membrane filtration (including ultrafiltration, microfiltration, ceramic membrane filtration, etc.), as well as the use of force methods such as adding coagulants, clarifying agents, or precipitants for clarification.

Among them, centrifugal filtration is a physical method that can be used alternately in multiple stages, but the process is cumbersome and time-consuming; The use of coagulants, clarifying agents, or precipitants may improve the clarity and cold solubility of the product, but the addition of exogenous substances has a certain impact on the yield and sensory quality of the product; Microfiltration is a process that utilizes the molecular sieve effect of microfiltration membranes to separate fine particles, suspended impurities, or turbid precipitate substances formed during processing from the quality components in the tea extract to achieve clarification. It has the advantages of high efficiency, no phase change in the process, no need to add exogenous substances, easy automation and continuous production, and has been widely used.

The clarification method of inorganic ceramic membrane microfiltration is significantly superior to natural filtration, suction filtration, and centrifugation. When the pore size of the ceramic membrane tube is between 0.1~0.8 μ m and the filtration pressure is between 0.2~0.3 MPa, the transparency of the filtered tea soup improves as the pore size of the membrane tube decreases. Usually, when producing instant green tea on a large scale, a 0.2 μ m membrane is used for microfiltration at 45 ℃ and 0.28 MPa. When the filtrate weight is 90% of the weight of the raw material liquid, it is better to add 15% of the weight of the raw material liquid for dialysis twice. The instant tea set produced by using a ceramic membrane with a pore size of 0.1 μ m and filtering at a temperature of 10 ℃ has good cold solubility.