Drying and Fragrance Adjustment of Instant Tea

Drying of instant tea

The main purpose of the drying process is to remove moisture from the concentrated solution, shape the appearance, fix the quality, and obtain instant tea products. The moisture content of dried instant tea is generally required to be less than 4%. At present, in industrial production, there are three main drying methods for instant tea: spray drying, freeze drying and vacuum drying.

Spray drying is one of the most widely used methods in the processing of instant tea. Its basic principle is that the concentrated liquid is sent by high-pressure pump to the pressure or centrifugal nozzle for atomization, and the air is filtered and heated into the spray drying tower. The particles are formed by convection drying. The finished particles are discharged from the tower bottom, the fine powder is collected by the cyclone separator with the exhaust air, and the water vapor is extracted by the induced draft fan with the exhaust air. The main factors affecting the efficiency and effect of spray drying are the type of nozzle, the temperature of hot air, the concentration of liquid feed, and the flow rate of liquid feed. The spray drying method has the advantages of high drying efficiency, large production, beautiful product appearance, uniform particles, good fluidity, etc. It is suitable for the processing of popular instant tea products.

The basic principle of freeze-drying is to freeze concentrated tea juice at low temperatures, and then vacuum dry it at a pressure lower than the triple point of water (609Pa) to directly convert ice into water vapor and remove it, and obtain flaky products. The drying efficiency of freeze-drying method is relatively low, but the quality of the product such as color, cold solubility, and aroma is good. The product is in the form of flake like crystals with a low packing density, which is suitable for the processing of high-end instant tea.

Vacuum drying is rarely used in the industrial processing of instant tea due to its low drying efficiency, and the relatively high temperature and vacuum can cause a decrease in the aroma, taste, and color quality of the product.

Aroma recovery and blending of instant tea

In the processing of instant tea, after the extraction, concentration, and drying processes of tea leaves, there is a significant loss of volatile aroma substances, which often leads to low tea aroma in instant tea products. Therefore, in the extraction process, collecting and condensing the tea aroma, and then adding it to instant tea in the drying process, is an important technical measure for preserving the aroma of instant tea. There are many methods for aroma recovery, mainly steam extraction, supercritical CO extraction, and distillation.

The principle of steam extraction method is to use steam or inert gas as the fragrance medium, stimulate the aroma in tea leaves, collect it on a certain carrier through a cooling plate, and then mix it with concentrated liquid to dry and prepare instant tea, or spray it into instant tea by atomization after drying to achieve the purpose of preserving aroma. This is the extraction and recovery technology of tea aroma. The operation method is usually as follows: high temperature steam – excitation of tea aroma volatilization – cooling coil cooling of tea scented steam – water liquid distillation – fragrance essential oil emulsion → mixing according to the tea juice concentration required for spray, then spray drying, or even direct spraying on the dried instant tea particles.

It is worth noting that when using the direct spray method, the mist particles must be fine and uniform, and the moisture content of the dried instant tea must be controlled below 4%. When using steam for extraction, the steam volume is usually 4% to 5% (mass fraction) of the tea extract, and the mass of the separated water-soluble aroma components is 3% to 4% of the tea extract. This method is simple in equipment and convenient in operation, but the essence obtained by this method only contains aroma components, and no taste components.

The supercritical CO extraction method mainly uses CO as a fragrance medium to extract tea aroma, which has a strong ability to dissolve tea aroma components. The aroma extraction process can maintain a low temperature, and CO recovery is also easy. Therefore, it has the function of preventing changes in aroma components. The extracted aroma components can also be directly introduced into the concentrated tea extract, which can regulate the loose density of instant tea. Supercritical extraction method for extracting tea aroma has low extraction temperature, minimal damage to aroma components, and high fidelity of aroma, but requires high equipment technology.

The fractionation method is mainly to collect the escaped tea flavor gas through special devices. After rectification, the flavor liquid is mixed with the tea concentrate before drying in a certain proportion, and then dried by spray, or sprayed directly on the instant tea particles with water content below 4% in a small amount and evenly.

In addition, there are various techniques to enhance the aroma of instant tea, such as tea aroma modulation, flower and fruit aroma modulation, and micro gel technology modulation. Adjusting the aroma with tea aroma refers to adding some high aroma tea to the raw material selection process and processing it into instant tea. In the processing technology, an aroma recovery process is added, and the recovered tea aroma is used to adjust the aroma of instant tea.

Aroma blending with floral and fruity notes involves using organic solvents to extract the aromatic components from the floral and fruity notes, removing the solvent to obtain aromatic oil. This aromatic oil can then be sprayed onto powdered tea extract, or the floral and fruity notes can be processed together with the tea leaves. Microcapsule technology, also known as microencapsulation, refers to the process of using polymer encapsulation materials to encapsulate substances in a miniature, semi permeable or sealed capsule. The encapsulated material is separated and isolated from the outside world to achieve maximum preservation of the original flavor, performance and biological activity of food and beverages. Generally, the extracted and recovered tea essence is used as the heartwood, and 8-cyclodextrin is used as the micro glue wall material for spray drying, which can effectively maintain and enhance the aroma of instant tea.