Monday, April 09, 2007

Astringency: The Red-Headed Stepchild of Tea's Flavors

Introduction

Astringency is quite possibly the least understood of tea's veritable cornucopia of flavors. Many people know it only as an unpleasant bitterness, but I would argue that this is NOT necessarily the case. While too much astringency can taste awful and bitter indeed, a total lack of astringency can leave your tea tasting flat and boring. The right amount, though, can add complexity and intrigue to your standard cuppa.

From my experience, I have noted four (4) kinds of astringency that can be found in tea-- some good, some bad. I must confess that I was only able to name / classify them after reading Kam Leung's page on what makes a good cup of Chinese tea, though I have slightly modified his list to better reflect my observations. So, without further ado...

The Four Types of Astringency
1. Rough Astringency

This is the kind of astringency that we have all likely noticed at one point or another. This is the unpleasant, extremely drying form of astringency that is not usually sought-after. This taste will leave your tongue uncomfortably dry for a prolonged period of time. Kam calls this type "Se."

2. Neutral Astringency

This type of astringency isn't really anything to write home about. This type will still leave your tongue feeling dry, but not nearly as uncomfortably as rough astringency will. Though I don't particularly like this type of astringency, I don't hate it either, and some people actually enjoy it. Often this is a natural property of the tea, and will come out no matter what, but sometimes it is a result of over-steeping or using too many leaves. Kam calls this type "Ku."

3. Stimulating Astringency

This is the kind of astringency that I love and crave. It is unique in that it seems to stimulate your tongue to produce excess moisture, and leaves your tongue feeling oddly dry and wet at the same time. It can also produce a kind of cooling effect when you breathe. Kam notes that this is also a minty feeling, and calls it "Gan."

Kan also describes "Hui Gan," which is a prolonged stimulating astringency (minutes to hours). This is very rare, and very very nice. I have only experienced this once or twice, as you need a very high quality tea and the brewing has to be right on the spot. I've only experienced this with the Makaibari Vintage Muscatel Second Flush Darjeeling that I reviewed earlier, but I'm sure there are others out there that can produce this wonderful effect.

4. Metallic/Organic Astringency

This type of astringency is absolutely awful. It may simply be an extreme form of rough astringency (Se), but it is so horrid that I think it deserves its own category. I have most often encountered this astringency when brewing gyokuro (shaded Japanese green tea) with water that is far too hot, but it can manifest itself in other non-/lightly-oxidized teas as well when brewed with too much leaf or too much heat. As you could likely surmise from the name, this type of astringency is marked by a metallic, yet also strangely organic taste. If I ever get this in my tea, I just throw out the entire infusion. Note that if you get this flavor, it is almost definitely a result of human error-- I don't think any producer makes tea that intentionally tastes like this.

The Science behind Astringency

Though I have absolutely no idea what causes one type of astringency to present itself versus the others, but I can share a bit about the basics behind the chemistry of astringency. Despite what you may have heard, tannins are not responsible for astringency or bitterness in tea. There are essentially zero tannins in tea. As far as I can tell, the word "tannins" only became part of the tea lexicon because tannins cause astringency in wine, and someone just ported it over to describe tea. The correct term for the compounds that cause astringency in tea is polyphenols. Though tannins are also polyphenols, not all polyphenols are tannins.

EGCG Chemical StructureThe simplest polyphenol is just an aromatic ring with two or more hydroxyl (-OH) groups attached to it (as opposed to an aromatic ring with only one hydroxyl, which is simply called phenol), but biological polyphenols are often much more complicated than this. The majority of polyphenols found in tea are catechins, which make up about 25% of the leaf's dry weight, such as EGCG (epigallocatechin gallate), shown here.

Polyphenols cause the astringent sensation by binding with salivary proline-rich proteins (proline is one of the 20 main amino acids, and is quite unique in its structure) to form insoluble chemical complexes, thus reducing salivary lubrication, causing a drying sensation in the mouth. An abstract discussing this mechanism can be found here).

***Somewhat related notes: During processing, some of these polyphenols are oxidized to theaflavins and thearubigins, which give black tea some of its flavors and colors. Also, polyphenols such as EGCG have been shown to have potent antioxidant properties, which has attracted quite a bit of attention (thanks Snapple) as of late.***

The Bitter End

Though it is often looked down upon and considered as nothing more than bitterness, I think the right kind of astringency can be one of tea's most interesting characteristics. Hopefully, this information will allow many of you tea drinkers to more fully appreciate the astringent qualities of tea, or at least think twice about using the word "tannins" ever again (please, I'm begging you).

9 comments:

Salsero said...

Brent--

I certainly am pleased to see someone tackle this difficult yet central issue in tea taste. Nigel from Tea Craft commented in another forum that grapefruit skin is bitter (another term often confused with astringency) and unripe banana peel is astringent. But I think you've made a strong case here for some version of Kam's multiple types of astringency.

Certainly some teas suffer from a lack of "bite" just as much as others suffer from too much.

Also, I'm proud to say that I think I understood a least part of the chemistry.

Thanks for the post.

Mary R said...

Ok, tomorrow I shall read your post with my full attention...but right now I'm just too distracted by all the pretty!

Wonderful design changes. My favorite part is actually the green to white fade behind the post text. It really sets it off from the side bar, and the distinct lack of white makes the whole page much easier to read. Gorgeous!

~ Phyll said...

Guilty!

Wonderful write up! But according to Mr. Sanwar M. Changoiwala, the director of the Gopaldhara tea company in Darjeeling, there is still some tannin in tea, though only in trace amount. Your point is well taken, however.

See Cha Dao November 9, 2006 post "Notes on the Biochemistry of Tea."

Brent said...

Yes, there are trace amounts of tannins, but they don't contribute much in the big picture so essentially there are none. You are right though, good catch!

MarshalN said...

Very interesting....

Do you think they are all caused by the same compound, or are there subtle differences in the chemical composition of said polyphenols that cause it to react differently in different teas?

If you want to get a good "huigan" note, a potent young puerh should do it. In fact, I can probably find you some and send it to you if you can't seem to locate any tea that does it for you.

"Ku" is just bitter in Chinese. I would think that what causes bitterness in tea is caffeine, not polyphenols?

Brent said...

MarshalN-

I think you're on to something with the differences in relative amounts of multiple polyphenols. Unfortunately this is a very difficult thing to test scientifically, so I doubt that there will ever be a clear cut answer.

As for caffeine... I'm not so sure. If that were true, one would expect only the first infusion of some teas to be very bitter, and later ones to have no bitterness because of the decrease in caffeine. Still, it could definitely play a role as one of many bitter compounds, so I wouldn't rule it out completely.

Proinsias said...

I was under the impression that it was mainly in low quality, tea-bag-esque, tea that the caffine was extracted from the tea quickly. Whole leaf tea would, I imagine, be little more reluctant to release all it's caffine in the first few short brews.

I have occasionaly poured away the first one or two brews hoping to avoid most caffine intake and still ended up staring at the bedroom celing, unable to sleep, for extended periods of time - not exactly a peer reviewed study but enough to convince myself that all the caffine doesn't vanish quickly.

Lewis said...

As for caffeine... I'm not so sure. If that were true, one would expect only the first infusion of some teas to be very bitter, and later ones to have no bitterness because of the decrease in caffeine. Still, it could definitely play a role as one of many bitter compounds, so I wouldn't rule it out completely.

(Sorry for the late response.)

While caffeine does get flushed from the leaves faster than a lot of components, the idea that it all comes out in 30 seconds is strictly folklore. And it's quite common for the liquor to get less bitter over a series of infusions, so I think caffeine is a likely cause for a big proportion of most teas' bitterness.

Brent said...

Lewis:

Since writing this, I too have come to learn that the supposedly sudden drop in caffeine after 30s is rubbish. Thanks for the correction, though, I forgot I had written that here.

Regarding caffeine and bitterness, I'm still sticking to my guns that polyphenols are the cause for most of tea's bitterness. Just like caffeine, the polyphenols are not all lost in the first brew, so they could still be the source of bitterness in later infusions.

Caffeine is a bitter substance (Ever tried those caffeinated mints? Nasty!) so it may indeed add to the overall bitterness of a brew. However, decaffeinated teas can be just bitter as unadulterated teas, so I'm hesitant to say caffeine plays a huge role.

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