Making Tea Without Caffeine
Although caffeine is the most widely used stimulant in the world, sometimes you want decaffeinated tea.
Caffeine is the world’s most popular drug. It is a central nervous system stimulant that directly affects the cardiovascular system, stimulating the heart rate. It also increases the activity of neurotransmitters like dopamine, heightening brain activity. Because caffeine increases heart rate, it’s not always suitable for everyone.
Tea from the Camellia sinensis plant contains over a hundred chemical compounds, including caffeine. Decaffeinated tea must undergo a process to remove the caffeine from the leaves.
In The Science of Caffeine: The World's Most Popular Drug, the American Chemical Society states,
“Scientists have found 400 milligrams is the safest average dose of caffeine for adults. To put that in perspective, that’ll be around three eight-ounce cups of coffee, five eight-ounce Red Bulls or a whopping eight cups black tea… Caffeine becomes toxic around 10 grams.”
Eight cups of tea are way too much of a caffeine kick for many people. (Visions of Seinfeld’s Kramer entering a room come to mind.)
Tea chemistry
Tea is a rich source of antioxidants, but it also contains high levels of caffeine, which may cause adverse effects in some people. Hence, the demand for decaffeinated tea.
You may be wondering exactly how caffeine is removed from tea. And is it safe?
First, a little tea chemistry will help you understand what's happening in your tea leaf.
The caffeine in tea is different from that in coffee because of how it bonds. Caffeine in tea combines with tannins, decreasing and stabilizing caffeine's effects. The tannins prevent the caffeine from being released too rapidly, absorbing it over a longer period.
However, the l-theanine in tea naturally balances the stimulant effects of caffeine. The unique combination sharpens the mind, increases concentration, eliminates fatigue, and enhances intellectual acuity. Coffee does not contain theanine.
READ: The Ingredient Found Only in Tea
Caffeine is a methylxanthine. Theobromine and theophylline are the other methylxanthines found in tea. The tea plant creates these chemicals to protect itself from insects and other animals.
Methylxanthines make up 2% to 5% of the dry weight of the fresh tea leaves and contribute to the bitter taste of tea. The amount of methylxanthines in tea depends on the variety and cultivar of Camellia sinensis, the age of the leaves, the climate, and the propagation method.
How much caffeine is in tea?
Dry Leaf Caffeine Content:
Caffeine accounts for 14 -28 mg/g of the tea leaf in fresh tea leaves. The levels of caffeine vary depending on the tea plant variety or the tea leaf harvested. Fresh tea leaves from growing shoots contain higher amounts of caffeine than older leaves.
Brewed Leaf Caffeine Content:
Brewed tea may have anywhere from 15 -75 mg of caffeine per 8-ounce cup. The level of caffeine in brewed tea varies depending on the amount of tea used, the type of tea, the volume of boiled water, the brewing temperature, and the brewing time. The hotter the water, the more caffeine is extracted.
Caffeine-free vs. decaffeinated tea
All teas made from Camellia sinensis contain caffeine. Even decaffeinated tea retains a small portion, about 10 mg per cup. Numerous decaffeination methods remove caffeine from tea derived from the Camellia sinensis plant.
Caffeine-free herbal teas are naturally caffeine-free. The only exception is Yerba mate, which contains caffeine. Herbal teas do not go through a decaffeination process.
Decaffeinated teas have had the caffeine removed. Historically, the tea industry used three main methods to remove caffeine from tea leaves. Tea makers chose the Carbon Dioxide, Ethyl Acetate, or Methylene Chloride method.
How is tea decaffeinated?
Caffeine is efficiently extracted using boiling water or water-organic solvent mixtures. The extraction of caffeine in tea is low when using cold water.
Decaffeination is when a solvent removes the caffeine from tea leaves. To decaffeinate tea leaves, a solvent is mixed with oxidized tea leaves. After several hours, the solvent and the dissolved caffeine are removed, and the leaves are dried.
Methylene Chloride used to be the solvent of choice, but health concerns led to its ban in the United States.
Today, two methods are most common:
Ethyl Acetate
Ethyl Acetate was the first solvent used. It is not very effective in removing caffeine, and it also removes some of the flavor-providing compounds within the leaves.
Supercritical Fluid Extraction with Carbon Dioxide (SFE-CO2). (Sometimes abbreviated as Supercritical Carbon Dioxide (CO2) extraction).
Supercritical Carbon Dioxide is a better choice; it can remove caffeine without affecting other compounds within the leaves.
Look for decaffeinated decaf teas using the Supercritical Carbon Dioxide process, which retains the most flavor and antioxidants.
How exactly do these processes remove the caffeine to create decaf tea?
Researchers at the University of Newcastle, Australia, explain how Ethyl Acetate, Carbon Dioxide, and Water create decaf tea.
Decaffeinating tea using ethyl acetate
Organic solvent decaffeination is generally done by first softening the tea leaves in water and mixing in the organic solvent of choice. At room temperature, caffeine is about ten times more soluble in organic solvents than in water.
Most of the caffeine is extracted from the leaves, but the other significant tea components, the catechins and theanine, remain in the leaves.
Ethyl Acetate is a standard solvent for extracting caffeine and polyphenols from teas. It is entirely digestible and found in many fruits, such as apples, peaches, and pears. It has been used in various foods, such as salad dressings and fruit desserts, and has been approved for decaffeination by the U.S. FDA since 1982.
Ethyl Acetate is the solvent of choice compared to the other organic solvents used to prepare decaffeinated tea products.
Decaffeinating tea using carbon dioxide
Due to increased consumer concerns toward chemical residues in decaffeinated products, Supercritical Fluid Extraction with Carbon Dioxide (SFE-CO2) is a selective and viable method for removing caffeine from teas.
Kurt Zosel discovered the Carbon Dioxide decaffeination method in the early 1970s. To decaffeinate tea using SFE-CO2, the tea leaves are soaked in a co-solvent to enhance the caffeine extraction.
Liquid carbon dioxide is pumped in at a designated pressure. It is then heated and pumped into the extraction vessel to extract the caffeine from the tea leaves.
Caffeine dissolved in supercritical carbon dioxide is separated from the carbon dioxide and collected by reducing pressure. Since flavor molecules are larger than caffeine molecules, they remain intact, so tea's flavor remains the same.
The outcomes of the decaffeination process using SFE-CO2 vary depending on the tea particle size, the co-solvent utilized to soak the tea in, and the temperature, pressure, and flow rate of the CO2.
The main limitation of the SFE-CO2 decaffeination method is the high costs. However, this is outweighed by several advantages. It is a fast process with no toxic residues, less degradation of the tea catechins, and high retention of the tea flavors.
Decaffeinating tea using water
Water is a safe and environment-friendly solvent, relatively inexpensive and accessible compared to organic solvents.
Therefore, it is usually considered a solvent of choice for any separation or isolation process.
Water was initially used for the decaffeination of coffee in 1938. Since then, two types of water extraction methods have been developed to decaffeinate coffee beans:
The Swiss Water decaffeination techniques.
French Water decaffeination techniques.
The advantage of the Swiss Water process is that it produces decaffeinated coffee beans with a richer flavor. In contrast, the benefit of the French Water process is that it results in decaffeinated coffee beans with higher solids and less moisture.
The advantage can be potentially applied to water decaffeination of tea to minimize the loss of flavor.
Water decaffeination process
Water decaffeination is done by first blanching freshly harvested tea leaves in boiling water for a short time. As the water solubility of caffeine is higher than the solubility of the tea catechins, most of the caffeine can quickly be extracted into the boiling water. In contrast, the catechins mostly remain behind in the tea leaves.
The leaves are quickly removed from the boiling water containing the caffeine and dried to obtain decaf tea.
The water decaffeination process is influenced by:
Water temperature
Length of blanching time
The ratio of water to tea
The type of fresh tea leaves used
The water decaffeination process is inexpensive and does not risk organic solvent residues being left behind in the decaffeinated product.
However, this method may cause the loss of flavor and theanine, a valuable amino acid unique to tea in the plant world. And who wants tea without theanine?
Decaffeinating tea at home
A once-popular solution to removing caffeine at home was to rinse your tea first. Perhaps the idea came from the water decaffeination process. However, rinsing doesn't remove as much caffeine as people thought.
Bruce Richardson of Elmwood Fine Teas, author of many tea books, helped sponsor a university study that measured caffeine content in eight classic loose teas. The researchers found that a three-minute infusion removes only 46-70% of the caffeine from a cup of tea.
Studies at Asbury University showed that a six-minute soak would remove 80% of the caffeine. Discarding the first infusion remains a viable way to reduce caffeine intake; know it's not 100% decaf tea. This method works better for green tea than it does for black tea.
Does decaffeinated tea contain theanine?
Yes, decaffeinated tea still contains l-theanine, although typically in slightly reduced amounts, compared to regular tea.
L-theanine is water soluble and naturally present in the leaves of the Camellia sinensis plant.
The decaffeination process can cause some loss of l-theanine, especially if done using chemical solvents.
CO2 or water-based decaffeination tends to preserve more theanine and polyphenols.
Teas with the most and least caffeine levels
If you want to know how much caffeine is in your favorite tea, the book Tea: History, Terroir, Varieties by Kevin Gascoyne et al. presents a biochemical analysis of 35 teas. The table lists the concentration of caffeine in various tea infusions. The authors tested the caffeine levels by preparing the teas as you would at home.
Not surprisingly, matcha topped the list for the highest caffeine levels at 125 mg/100 ml (3.5 fl oz). Matcha is a ground powder from the whole tea leaf. You consume the entire leaf, not an infusion of the tea leaf.
Many people drink green tea, thinking it’s lower in caffeine. However, this table notes that some green and oolong teas have higher or equal caffeine content than black teas.
Here are some of the highlights of the study:
All teas (except matcha) were infused in a teapot with 2 cups (500 ml) of water.
Matcha (powdered green tea) had a concentration of 126 mg of caffeine.
Sencha (Japanese green tea) had 12 mg of caffeine.
First flush Darjeeling had 58 mg of caffeine.
Longer infusions and higher water temperatures release more caffeine.
The authors also found that a 10-minute infusion extracts 70% of the caffeine from the leaf. This study is consistent with the study done at Asbury University with Bruce Richardson and the chemist Michele Francl, author of Steeped: The Chemistry of Tea.
Low caffeine & decaffeinated tea
All herbal teas (tisanes), except for yerba mate, are caffeine-free.
Kukicha or twig tea
Kukicha is a Japanese tea made from the stems of sencha, kabusecha, or gyokuro. Kukicha may also be called bocha or stick tea. Because only the stems are used, this tea is naturally low in caffeine. When the stems are from gyokuro production, kukicha is often called karigane.
Hojicha
Hojicha is roasted bancha or sencha and kukicha twig for a savory, nutty flavor. One of the things you will notice with hojicha is its roasty aroma. Hojicha brews a caramel amber color with a sweet, biscuity, and nutty flavor. Even though it's low in caffeine, the flavor is robust.
Most reputable tea companies will tell you the methods used to decaffeinate their tea. Adagio Tea sells decaffeinated tea using the superior carbon dioxide (CO2) process. Check the labels on your favorite decaffeinated tea or their website.
References
Kevin Gascoyne, Francois Marchand, Jasmin Desharnais and Hugo Americi, (2014). Tea: History, Terroirs, Varieties. Firefly Books Ltd. pp. 254. ISBN 978-1-77085-319-5
Michelle Francl, (2024). Steeped: The Chemistry of Tea. Royal Society of Chemistry. pp. 70-77. ISBN 978-1-83916-591-7
Quan V. Vuong & Paul D. Roach (2014) Caffeine in Green Tea: Its Removal and Isolation, Separation & Purification Reviews, 43:2, 155-174, DOI: 10.1080/15422119.2013.771127