Manufacturer and Supplier of Orthodox Tea Processing Machinery in Kolkata

 

 

WHY WITHER TEA LEAVES

Traditionally, there are a bunch of reasons why fresh plucked tea leaves are withered. Most of these reasons deal with the machinery & techniques involved in the manufacturing process. Let’s take a quick look at these.

 

Mechanically, withering is important because it reduces moisture content and makes the leaves flaccid. These two attributes assist in the rolling and drying process. They make the leaves easier to deal with. This then allows more consistent processing, and generally keeps the leaves from gunking up the machinery. For instance, many factories use a fluidized (vibrating) bedplate in their driers, passing the leaves through different drying regions of the machinery. Too wet a leaf, and it balls up and sticks to the machinery, gumming up the works. The same goes with factory rollers, with too-wet a leaf clogging the rotorvanes.

 

 

Also mechanically, but not so much in terms of machinery, the reduction of moisture is used in large-scale fermenting. If there’s too much moisture, the dhool (fermenting tea leaves) won’t be properly aerated, and temperature control is more difficult. However, there’s a fine line because too much moisture loss and the enzymes in the leaf won’t properly ferment the leaves. This brings us along to the next topic…

 

WHAT HAPPENS DURING A WITHER

A handful of changes occur in tea leaves during the wither process. All physiological / biochemical. All important. Let’s begin by looking at the changes mentioned in the above section that assist the mechanical-side of things when it comes to tea manufacturing.

 

THE TEA LEAVES GO LIMP

After tea leaves are plucked, over the course of withering they become more flaccid. This softening up of the leaves occurs because the leaf membranes open up. This opening of the membranes makes them more permeable, but also weakens the leaf structure making them go limp.

 

 MOISTURE LOSS IN THE TEA LEAVES

 

This cell permeability is important for a couple reasons. To begin with, it assists in moisture-loss. A big component to tea manufacturing is to ultimately reduce the moisture content of tea leaves down to about 4%. This moisture loss, is important in terms of the smooth operation of the tea manufacturing equipment (as mentioned above), but also for the shelf-stability of the final “made” tea.

 

 OXYGEN ABSORPTION BEGINS

Another important reason for cell permeability is because it helps the internal cell workings begin absorbing oxygen. If you recall in my previous article on tannins in black tea, the fermentation process is actually an enzyme-assisted oxidation process—much like how bruised apples & bananas will brown. This oxygen absorption is very critical to the later fermentation process. It’s not used immediately because the enzymes that assist fermentation have not yet been activated by the full release of tea tannins.

 

 BIOCHEMICAL CHANGES

Biochemically a lot is going on inside those tea leaves, and it begins during the wither. These changes include enzyme activity, the coming and going of volatile compounds, and changes in organic acids & sugars. Furthermore caffeine content begins to increase, while we see a decrease in chlorophyll, lipids & fatty acids, and carotenoids. And of course we see the breakdown of amino acids and proteins.

 

If you recall our previous article on black tea tannins, you’ll remember that withering is an important step. Enzyme activity begins oxidizing the fresh leaf catechins into Theaflavins and Thearubigins. The main culprits performing this activity are the Polyphenol Oxidase, and Peroxidase enzymes.

 

During withering, we also see a breakdown of more complex compounds into their simpler components. This is when proteins will break into their constituent amino acids. This is also when complex carbohydrates break into their simpler sugars. Many of the amino acids will combine with some of these sugars to produce volatile compounds important to the flavor of black and oolong teas.

 

Speaking of volatile compounds, we see the same from lipids and fatty acids. These compounds break down during the withering process as well. They go on to create new volatile compounds, however they’re not as beneficial to the crafting of black and oolong teas. They are responsible for the grassy odor you can detect during withering. This odor eventually goes away as you create your “made” tea.

 

Carotenoids & chlorophyll are both pigments in the leaf, but their breakdowns contribute in very different ways. While both compounds assist in photosynthesis, carotenoids are yellowish in color. When they break down, they contribute to the increasing volatile compounds.

 

 

 

Chlorophyll is greenish in color and its breakdown is important in two ways. If there is too much chlorophyll by the end of the tea-making process, the result is a tea with grassy overtones. If you’re making a black tea, this isn’t desirable. For green tea, it’s a different story (and in fact, some green tea makers will promote the increase of chlorophyll in their plants. Think Matcha). The second way chlorophyll’s breakdown contributes to tea is providing the black color of the leaves. Some of this breakdown is aided by the later drying process as well.

 

Finally, we can’t forget our friend caffeine. Caffeine occurs naturally in all tea. During the withering process, however, its levels increase within the leaf. The more effective a wither, the more caffeine content in the leaf. Additionally, the more caffeine content, the better the “creaming” property of your final tea.