Main source of bitterness in green tea

I would think its tannic acid and catechins that cause the bitterness, not the caffeine.

It is my understanding that the tannins are what causes the bitterness in green teas, that’s why oversteeped teas have a tendency to be bitter, because the longer you brew the tea, the more tannins are released into the brew.

Using too high a temperature will also cause tannins to be released. Tannins also bind essential minerals, so you should plan to drink tea around your meals.

Yes, I agree that catechins add bitterness too, although they are usually described as adding astringency, so perhaps astringency increases the perceived bitterness?

However, it is undeniable that caffeine is bitter (and not astringent), you can look it up easily.

Houjicha and kukicha, teas low in caffeine also taste less bitter, is caffeine playing a role there?

Both coffee and cocoa are bitter, and they contain caffeine. Robusta coffee has more caffeine than Arabica and it’s also more bitter.

“Bitterness of tea is generally ascribed to the combination of catechins, saponin, caffeine, and amino acids. Depending on molecular weight, catechins can be bitter or astringent, whereas saponins are often described as acrid.”
souce: http://ajcn.nutrition.org/content/72/6/1424.full

I’m not talking about perceived bitterness, astringency or sourness. People may think something is bitter when it actually isn’t, especially when dealing with astringency, where the main agent is catechin (look it up, its always defined as astringent).

I only want to discuss pure bitter flavor, which like catechins, caffeine also imparts.

I’ve definitely heard that caffeine is a primary source of bitterness, but I’ve flipped through a few of my tea books and cannot find a source for that. Sorry, that’s no help.

Besides what everybody else said, the stage of harvest and the shelf life of the tea cause different levels of bitterness. For the fresh tea from different harvest date, usually later harvest has higher catechin contents and is bitter than earlier harvest. On the other hand, catechin of moderate amount has heavier taste and some tea drinkers even prefer later harvest than earlier harvest.

Oxidation of the tea throughout the year will cause more polyphenols to form and make the tea more bitter. Most (however not all) green tea will develop bitterness within a year sitting on the shelf. So for the grocery green tea labeled with expire date 1.5 – 3 years from production, bitterness is guaranteed.

Quality of the water is another consideration. I am especially careful to use Spring water for brewing Green and White tea. Any minerals or chlorine in regular tap water may cause bitterness (and other disgusting off flavors yuck!).