Assam tea production process | what does rolling oxidation mean? The Historical Story of Rolling Machine

Jackson's innovations and many related ones later stand out in two ways: first, they were not automated; and second, the processes they created had a huge impact.

Jackson's contribution was to greatly improve the critical rolling stage in black tea production. This stage is after the tea leaves are picked and wilted.

Rolling allows it to acquire the right ductility, moisture and blade structure, allowing oxidation processes to activate compound interactions. This forms the flavor, color and aroma of tea.

Rolling is a simple process, but involves very complex time and technology. It grazes the harvested leaves, and when it withers, it carries away the moisture. This opens the chloroplast cell in the green leaf without destroying, deforming or dividing it. It releases catalyst enzymes to start chemical reactions (fermentation oxidation).

Scientific summary gives molecular dynamics hints: "polyphenol oxidase begins oxidizing green catechins to form orange theaflavins." And then they aggregate into brown thearins." In layman's terms, it's "this is tricky, you have to do it right." It takes a lot of pressure, but it needs to be handled carefully. The leaves must be rotated and rolled continuously to form a shape.

In China, skilled workers also knead green leaves counterclockwise by hand. This Japanese technique is equivalent to a demonstration by a professional tea maker, moving hands back and forth to form neat round needles. For Assam black tea, the rolling of the tea leaves is entirely manual, drying the leaves on charcoal and then treading them into wooden crates for shipment.

A lot of heat is generated during rolling, especially in summer and autumn. It must be released at the right time to control the rate of polyphenol oxidation. Jackson's machine must provide a rotation of different leaves with and without pressure, maintaining uniformity in leaf structure while gently breaking cells.

The weight of each batch rolling is very large:100 kg is the standard batch unit and is carried out as a separate "batch". Later rollers rolled 500 kg at a time.

Jackson's innovation came at the right time. Assam tea cannot compete with Chinese tea because even with imported "coolie" labor, it cannot compete with China's low cost and high experience.

Productivity in Assam is very low and the burden of rolling is disproportionate. Crews often discuss working late into the night to get the job done before the leaves lose freshness, tiny details that can spoil output, from small to too big a handful a worker picks up, how tightly he or she holds it, the size and ventilation of the room.

His machine was amazingly complex, as the excerpt from the book below shows.

This level of detail is fifteen pages long. Jackson stood out for his originality in design, engineering talent and his knowledge of tea growing.

(Source: Alexander James Wall, Tea Factories and Tea Machinery, 1923). The book was a digital, out-of-print reprint; it was not a bestseller at the time, but it was informative and surprisingly interesting.)

Of course, all of this happened before electricity became universal. Steam, wood and coal power the engine. The climate is humid and corrosive-Assam is essentially a semi-virgin jungle. Spare parts can't come in by FedEx.

Electricity appeared in India in 1879, and the first electricity supply was a hydroelectric station near Darjeeling Tea Garden in 1890. The earliest street lamps in India were introduced in 1905, but electricity did not enter Assam until 1923.