Decaffeination Methods: Solvents vs. Carbon Dioxide in Tea Processing

Tea can be decaffeinated through three main processes: methylene chloride, ethyl acetate, and carbon dioxide. In the United States, only the latter two are permitted, as methylene chloride, though effective, is restricted due to health concerns. 

Both methylene chloride and ethyl acetate use similar processing methods, where the tea leaves are soaked in the solvent, which bonds with the caffeine. The leaves are then dried, leaving behind a decaffeinated product. 

However, carbon dioxide decaffeination is unique. This method employs supercritical carbon dioxide—CO2 under high pressure and temperature—acting as both a liquid and a gas to selectively extract caffeine while preserving the tea's natural flavors. This process is considered more natural and gentler on the tea leaves compared to the solvent-based methods, as it doesn't involve chemical residues. 

As consumer preference shifts towards natural and organic products, the carbon dioxide method is gaining popularity, aligning with the growing demand for safer, more sustainable food processing technologies.
Decaffeination Methods: Solvents vs. Carbon Dioxide in Tea Processing

Yellow tea

The many varieties of tea include white, yellow, green, oolong, black, and postfermented teas (such as pu-er).

Yellow tea refers to a type of tea processed similarly to green tea, but for yellow tea, the drying phase is slower and the damp leaves are allowed to sit and yellow. Yellow tea is traditionally made with leaf buds plucked in early spring. The buds are processed like Chinese green teas through the pan-firing step, or they are treated to a gentle heating method known as men huan or “sealing yellow”.

This is the rarest class of tea by far, difficult to source because the harvest time is short, and the processing is complex and time-consuming. Yellow tea originated in the Anhui an Hupei Provinces.

Although it might be the smallest category of tea based on to production volume, there are written records showing that yellow tea may have been produced as early as the Tang dynasty (618-907).
Yellow tea

Why white tea is good for you?

Perhaps first produced during the Tang Dynasty (618-907 AD), white tea was the preferred tea of the Chinese royal court.

White tea is so named because the silver fuzz that’s till covers the immature buds and leaves after they are picked turns white when they are dried. The leaves are steamed quickly after harvesting to prevent oxidation of polyphenols and then dried.

White tea contains high level of antioxidants because the leaves and buds are steamed and dried immediately after harvesting, locking in their antioxidant qualities. Because of this kind of processing, white tea contains far less caffeine than other types of tea.

The health benefits of white tea include:
*The polyphenols in white tea can help fight fatigue and wrinkles due to aging
*Because of its high antioxidant content, white tea can help prevent various cancers better than other types of tea by destroying free radicals
*Lower cholesterol and blood pressure. White tea contains more catechins than green tea it has better chance of lowering cholesterol
*Keep the heart and the whole of circulatory system healthy
*Stronger bones
*White tea can effectively bolster the body’s immune system
*Fluoride in white tea can help prevent tooth decay

The main reason why white tea is so much better for the body than any other type of tea is because it is the least processed type of tea.
Why white tea is good for you?

Tea decaffeination using ethyl acetate as a solvent

Decaffeination of tea is desirable to regulate caffeine intake. Decaffeinated tea is produced by removing 60% to 90% of the caffeine from black tea by solvent extraction.

The most common decaffeinating solvent is ethyl acetate.  Ethyl acetate is derived as a result of the reaction between ethanol and acetic acid.

This process considered a natural method because the compound occurs naturally in fruits, vegetables and other plants, tea leaves are bathed in water, washed with ethyl acetate to remove the caffeine and then dried.  This process leaves a maximum carrier residue of 1 ppm or less, and a maximum caffeine residue of .08 percent, dry weight.

The tea is 99.9 percent decaffeinated at the end of the process, and has 8 percent maximum water content when leaving the factory. Decaffeinated Ceylon Black is processed in this manner.

Tea decaffeinated using ethyl acetate loses up to two-thirds of its flavonoids content. This process is less expensive and some people detect a slight aftertaste.
Tea decaffeination using ethyl acetate as a solvent

Drying of tea leaves

Drying achieved by blowing hot air through tea leaves, arrests oxidation by inactivating enzymes, resulting in color enhancement and the final balance of tea aroma and reduces the moisture content of the leaves to less than 5%.

In Keemun black tea processing, the leaves are subjected to drying after fermentation at 110 °C– 120 °C for 10 – 15 min. The moisture will drop below 20%.

After spreading the first dried leaves, another drying is carried out at 70 °C – 90°C for 45 –60 min to moisture below 4%.

Drying is usually done by a drying machine such as the multi-band drier or fluid bed drier.

The temperature is sufficient to inactivate the polyphenol oxidases. The sap released during rolling and fermentation solidifies during drying on the fine little hair on the surface of the leaf.

During drying, aroma substances are formed and the coppery-red color is changed to black (hence ‘black tea’).

Following the drying the leaves are sorted and graded to yield a commercial product.
Drying of tea leaves 

Rolling of tea leaves

Once tea leaves are withered to the desired status, the leaves are fed into rollers and are lightly, without pressure, conditioned in order to attain a uniform distribution of polyphenol oxidase enzymes.

These enzymes are present in epidermis tissue cells, spatially separated from their substrates. This is followed by a true rolling step in which the tea leaf tissue is completely macerated by conventional crank rollers under pressure.

Once done by hand but now performed mainly by machine, rolling transforms the flat leaves into mesmerizing twists, coils, balls or spears.

The rolling process physically crushed the leaves, opening sand exposing the leaf matrix and cellular compartment providing a more homogenous mixture for oxidative reactions and amore extractable matrix for brewing.

Rolling times vary between ten minutes and one hour. Young leaves are rolled under lighter pressure and for shorter duration compared to older leaves, in order to prevent the leaf breakage and yellowing that results from hydrolysis of chlorophyll and autoxidation of polyphenols.

In general, lightly rolled teas have mellower and gentler flavors, while leaves rolled with greater pressure break up into smaller pieces and form brews that are more brisk and intense.
Rolling of tea leaves 

Hot Water Soluble Tea

Hot Water Soluble Tea
In country consuming the traditional hot beverage the instant product has not, so far, enjoyed the same fairly wide acceptance as has instant coffee. Only on the last few years has there been any serious attempt to market instant tea in the United Kingdom outside the catering and vending sector. The market is still in an early stage of development with several freeze dried products of reasonable quality consisting of 100% tea solids retailing alongside mixes containing whiteners or sugar and other flavoring.

The manufacturing process is essentially similar to that for instant coffee, namely the preparation of an aqueous extract, followed by concentration and drying of the extract to yield a completely soluble powder or granules. In the case of tea, however, control of the processing condition is much more critical of product degradation is to be avoided. The extract may be prepared from conventional black tea or from undried green leaf which may be partly processed before the extraction. In either event the extraction conditions must be precisely controlled in order to provide both satisfactory quality and a commercially viable yield. After extraction the liquors require very careful handling to minimize undesirable changes before the final drying step. This may be by spray drying or freeze drying.

For a retail product, marketing considerations dictate that the product density should be such that one tea spoonful of powder or granules corresponds to a cup of average drinking strength.
Hot Water Soluble Tea