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.
The 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).