A Storm in a Cup of Tea | Green Tea Cookies

Tea chemistry and processes. Green Tea Cookies.

There is nothing like green tea cookies to understand the chemistry of the processes that the drink goes from the field to the steaming glass.

Tea and coffee are the most consumed beverages in the world, except of course for clean water. Their popularity is related to their abundance of substances that create in us, humans, a stimulating feeling, although for the plants themselves these are simply chemical means of protection against pests and natural disasters. 

Over the years, humans have learned to dilute these substances and change them, and have fallen in love with their taste. Tea leaves and coffee beans have common defenses, such as caffeine, which is primarily identified with coffee, and the polyphenols we will focus on here.

Tea begins its journey as a leaf rich in enzymes that determine the nature of the final product: a glass of hot drink. Where does its unique flavor come from and what is the difference between the different types of tea? With the purpose of answering these questions, we present to you this time a delicious recipe for green tea cookies.

What will you need?

  • ¾2 cups white flour.
  • 2 tablespoons of green tea leaves from tea bags (about 4 bags). It is recommended to crush the leaves into a powder.
  • 1 teaspoon baking powder.
  • ½ teaspoon baking soda.
  • ½ a teaspoon of salt.
  • 1½ cups sugar.
  • 1 egg.
  • 1 teaspoon of vanilla extract.
  • 200 grams of soft butter left for a few hours at room temperature (or oil).

What to do?

  • In a bowl, mix the dry ingredients, except for the sugar, to a uniform mixture.
  • Whisk the butter with the sugar in a food mixer until an airy mixture is formed. Add the egg and vanilla while whisking.
  • Continue to whisk and add the mixture of dry ingredients in small portions. Make sure that the dough can be separated from the sides of the bowl. 
  • Wrap the dough ball in cling film and roll it into a roll about 5 cm in diameter. Wrap the edges well and refrigerate for at least half an hour.
  • Remove the dough roll from the refrigerator and slice without the plastic wrap into slices about 1 cm thick. Arrange the slices on baking paper and bake in a preheated oven at 180 degrees for about 12 minutes.
Green tea cookies.
Green tea cookies.

And now for the science

The tea plant is native to southeast Asia and southern China. The origin of its name lies in the Chinese word chá, which refers to a beverage made from the green leaves of the Chinese camellia (Camellia sinensis).

There are hundreds of varieties of this plant, and over the years people have developed methods to grow varieties with leaves that have the desired characteristics.

Two thousand years ago, the people of southwest China knew that techniques such as squeezing the leaves and heating them for a limited time make it possible to have tea in a variety of flavors.

Fine tea is made from the plant’s young leaves and unopened leaf buds, which are the most delicate and vulnerable and also have the highest levels of chemical preservatives and inactive enzymes. Nowadays, most commercial tea is harvested by machine, without careful selection of the leaves, so blends also contain mature leaves that have a less rich flavor.

How It’s Made: Tea.

Main stages of tea production

Immediately after picking, the tea leaves begin to wither. The processing process that the leaves go through at this stage greatly prolongs their life and also preserves their flavors and even improves them. This is a natural process that happens to the fruit and leaves after they detach from the mother plant.

The Withering process has a dual function. The first is the primary drying of the leaves. During Camilla, the amount of water in the leaves decreases by about 30%, which considerably changes its structure and adds flexibility, which will further facilitate its design. In addition, the Withering process is responsible for many chemical changes that occur in the leaves.

Fresh tea leaves have a bitter and even slightly pungent taste, which is due to the polyphenols they contain – a variety of colorless compounds from the phenol family, whose function is to protect the plant from pests. After harvesting, the leaves are crushed and left in the air for a limited time so that the enzymes they contain – proteins that accelerate certain chemical processes – can act in the presence of atmospheric oxygen.

Under the influence of enzymes, phenolic compounds change and become substances with a different taste and darker colors. Short-term exposure to enzyme activity produces a very bitter and slightly pungent yellowish compound called theaflavin, while longer exposure produces, among other things, Thearubigin – a more complex compound that tastes somewhat less bitter. The longer the exposure time, the darker the color of the tea and the richer its flavor.

Chemical changes that happen in the tea leaves during production.
Tea Manufacturing Process.

After harvesting, the leaves are forcibly crushed or injured in other ways to break down the cellular structure and release their components. To control the taste and intensity of tea one must control the oxidation of the leaves, through strict control over the temperature and humidity at which they are kept. In the process of oxidation the chlorophyll (the substance that gives the leaves their green color) is broken down under the influence of enzymes, in a way that changes the color of the leaves and their taste and aroma. 

To slow down or stop the oxidation, the leaves are moved to a new storage place where the temperature is higher. During heating the enzymes are damaged or destroyed and thus it is possible to control the duration and intensity of oxidation

The oxidation process plays a key role in creating many flavor and aroma compounds that determine the type of tea we receive. If it is not done properly, unwanted flavors may form.

After the leaves have been oxidized and processed, an additional drying process is carried out, followed by hot air flowing over the leaves. The final drying ensures that the chemical reactions stop and bacteria and fungi have difficulty developing.

Tea classes by colors

We all hear about red tea, white tea, green … but what difference is there between all these varieties of tea? As we said, all of them come from the same tea plant, but their difference lies in the process that their leaves undergo within the factory where they are made. The main types of tea are:

  • White tea
  • Green tea
  • Yellow or gold tea
  • Blue tea (also called Oolong)
  • Red tea (known in the West as black tea)
  • Dark tea or fermented tea (which includes Pu’er)

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