Why green tea turns bitter - the chemistry of catechins and temperature
You know that feeling when green tea, which was supposed to be refreshing and delicate, turns out to be unpleasantly bitter and astringent? Many people then conclude that they simply do not like green tea or that they got a poor product. In fact, most often the fault lies not with the tea itself but with the way it is brewed. Green tea is extraordinarily sensitive to temperature and time, and a small mistake can turn a subtle infusion into a bitter brew. The bitterness is caused by compounds called catechins and by how they react to high temperature. Understanding this chemistry lets you brew green tea so as to draw out its sweetness and freshness instead of bitterness. Here is what really happens in the cup and how to save the flavor with a simple change.
Where the bitterness in tea comes from
The bitter and astringent character of green tea comes above all from a group of compounds called catechins. These are a type of polyphenol, natural substances present in tea leaves, to which many health properties are attributed. The most important and best-known catechin in green tea is the compound denoted by the abbreviation EGCG. Catechins are responsible for the astringency and part of the bitterness of the infusion, and to this is added caffeine, which is itself bitter. When too much of them ends up in the infusion, the tea becomes unpleasantly bitter and astringent. The key to good flavor is therefore drawing out of the leaves the right, moderate amount of these compounds. How much catechins and caffeine end up in the cup depends mainly on the temperature of the water and the brewing time, and these are precisely the two factors easiest to control at home.
The role of water temperature
Water temperature is the most important factor deciding whether green tea comes out bitter or mild. The hotter the water, the more intensely and quickly it draws catechins and caffeine from the leaves, and therefore also bitterness and astringency. Boiling water at a temperature close to one hundred degrees literally forces the excessive release of these compounds, which floods the infusion with bitterness. Cooler water, by contrast, draws them out more gently and selectively, allowing balance to be preserved. This is why green tea is usually not doused with boiling water but with water of a lower temperature. The optimal range for many green teas lies roughly around seventy to eighty degrees. It is the range in which the infusion keeps its freshness, sweetness and subtlety, and the bitterness stays under control. Simply changing the water temperature is often the simplest and most effective way to improve the flavor of green tea.
What happens to EGCG at high temperature
At high temperature, more happens to catechins, and especially to EGCG, than just more intensive extraction. Chemical transformations occur that change the structure of these compounds. One of the processes is so-called epimerization, that is the conversion of EGCG into a related compound with a slightly different spatial structure. This transformation intensifies at very high temperature. It is accompanied also by the breakdown and oxidation of catechins. The result of these changes is a shift in the flavor profile, in which the delicate freshness gives way to greater bitterness and astringency. In other words, the more strongly and hotly we brew green tea, the more we change the chemistry of the catechins toward a less pleasant taste. This is why brewing at a lower temperature not only draws out less bitterness but also better preserves the original, beneficial structure of the valuable compounds contained in the leaves.
Why tea turns bitter as it sits and cools
Many people notice that green tea tastes worse when it is left for a while and allowed to cool. Several mechanisms contribute to this at once. First, if the leaves are still in the infusion, they continue to release catechins and caffeine into it, so with every minute the tea becomes stronger and more bitter. Second, in the cooling infusion the catechins undergo further transformations and oxidation, which changes the taste for the worse. Third, our perception is also at work, because we sense bitterness more strongly in a cooler drink than in a hot one. Warmth partly masks the bitter taste, and when the tea cools, the bitterness becomes more pronounced. These factors together mean that the same tea, tasty right after brewing, can be clearly bitter after several dozen minutes. This is why green tea is best drunk fresh, and the leaves removed right after brewing.
The significance of brewing time
Alongside temperature, the second key factor is time. The longer the leaves remain in the water, the more catechins and caffeine pass into the infusion, and therefore the greater the bitterness. Green tea is very sensitive in this respect, and it is often enough to brew it briefly, sometimes only a few dozen seconds, to obtain a good flavor. Leaving the leaves for many minutes, as with strong black tea, almost guarantees a bitter result. This is why control of time is as important as control of temperature. Brief brewing lets you draw the pleasant aromas and sweetness from the leaves before an excess of bitter compounds passes into the infusion. Moreover, good green teas can be steeped several times, each time briefly, enjoying different facets of the flavor. This is a far better approach than one long, hot brew that squeezes all the bitterness from the leaves at once.
How to brew green tea without bitterness
From this chemistry comes a simple, practical recipe for mild green tea. First, do not douse it with boiling water but with water of a lower temperature, roughly in the range of seventy to eighty degrees. If you do not have a kettle with temperature control, it is enough to boil the water and wait a few minutes for it to cool a little. Second, brew briefly, starting from a few dozen seconds and adjusting the time to your own taste. Third, remove the leaves from the infusion right after brewing, so they do not continue to release bitterness. Fourth, make use of the possibility of steeping good leaves several times. These simple rules make green tea sweet, fresh and subtle instead of bitter. Most people who claim they do not like green tea have in fact been drinking it badly brewed. A small correction of technique can completely change the experience and reveal the true character of the infusion.
Why matcha follows different rules
It is worth noting that matcha, that is powdered green tea, behaves a little differently. With matcha we do not brew the leaves and then remove them, but drink the whole powdered leaf whisked into water. This means we consume all the compounds contained in it, including catechins, with no possibility of leaving them in the leaf. This is why with matcha the quality of the powder and the right water temperature, usually also lower than boiling, are especially important. Cheap, bitter matcha powder doused with too hot water will give an unpleasantly astringent drink. Good matcha, properly prepared, keeps its sweetness and characteristic umami taste. This shows that the same chemistry of catechins and temperature operates in different forms of tea, but the manner of preparation must be adjusted to whether we brew and remove the leaf or consume it whole as a powder.
Bitterness, health and flavor
An interesting aspect is that the compounds responsible for the bitterness, namely catechins, are at the same time those to which health benefits are attributed. So a certain tension arises between flavor and the content of valuable substances. Stronger, hotter brewing draws out more catechins, but at the cost of bitterness, and gentler brewing gives a more pleasant flavor but slightly fewer of these compounds in the infusion. It is not worth going to extremes, however. Drinking tea brewed so that it tastes good still provides many valuable substances, and the pleasure of drinking is as important as dry numbers. It is better to enjoy mild, tasty tea regularly than to force down a bitter brew in pursuit of the maximum content of catechins. The healthiest approach is to find a balance in which the tea is at once tasty and valuable, and on top of that drunk with pleasure.
Key takeaways
Green tea turns bitter mainly because of catechins, especially EGCG, and caffeine, which at high temperature and with long brewing are drawn out in excess and undergo unfavorable chemical changes. The tea also becomes clearly bitter when it sits and cools, because the leaves continue to release compounds, the infusion oxidizes, and we sense bitterness more strongly in a cooler drink. The solution is simple: brew with cooler water around seventy to eighty degrees, briefly, and remove the leaves and drink fresh. This small change of technique saves the flavor. If you want to experiment with brewing thoughtfully and record your impressions, GustoNote will guide you through it.