One of the many rewarding experiences of drinking tea is the savouring of the flavours in each sip. The true appreciation of the depths of flavour in a tea and how it begins, how it develops and then how it lingers afterwards is a never ending learning experience.
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In this series of blogs we will look at flavour in three ways. In our last blog we examined how we experience flavour when we drink, today we will look at why different teas have certain flavour. Finally in two weeks we we investigate the best way to taste tea.
Our last post looked at how we detect flavour from smelling, sipping and enjoying a lovely bowl of tea. In this post we will delve deeper into where those flavours come from with regards to the thousands of natural compounds that exist, change and interact within the magical leaf in its natural form and in processing. An understanding of the leaf’s chemistry helps a great deal in starting to work out why different teas taste as they do.
When looking at processing it is important to remember what you start with - the leaf. The chemical makeup of a leaf varies enormously depending on where it is growing, what variety it is and when it is being picked to name but a few factors. It also worth noting that these chemicals are not present to make a brewed leaf taste good! They all perform roles in the growth, protection and structure of the leaf and are effectively some of the raw ingredients present. We will now examine a few examples that will help our understanding later on:
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L-Theanine is an amino acid specific to tea used to make protein for plant growth and repair. It is responsible for the umami character in many teas and also is part of the Maillard reaction [more on this later in the blog] which give certain teas their nutty, caramel flavours.
Trichomes are small hair like structures
found on the leaf buds. A good example is
the Chinese white tea Silver Needle (Bai Hao
Yin Zhen). These can insulate the new
growth by keeping frost away from leaf cells,
help reduce evaporation or even protect the
leaves from insect attack. They also happen
to have an amount of essential oil at their
base which gives a tea a floral flavour.
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Carotenoids protect the leaf against sun damage and also helps the plant absorb UV light when light levels are low. When oxidation occurs they are converted into floral, woody, hay like aroma chemicals. One of these is β-Ionone which is present in all types of tea and provides a floral, violet aroma,
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Catechins also protect the leaf from UV light. Catechins are bitter and are also part of converting amino acids and carotenoids into flavour compounds.
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Glycosides are a combination of sugars and chemicals used by the plant for defence. The sugars basically act as a storage mechanism. When needed they are separated and only then do they provide flavour. There are higher amounts of glycosides in spring time meaning teas made then have an extra level of flavour.
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Cell membranes protect the cell, but also act as raw materials for grassy, vegetal and jasmine flavour compounds.
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Cell walls protect the cell membrane and contain enzymes that break down glycosides. They also contain cellulose which gives sugar that provides sweetness and is also is part of Maillard browning [see later]
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However, these raw ingredients start to change as soon as this leaf is picked. On plucking the chemistry of the leaf starts to change; it begins to lose moisture through withering resulting in the start of structural breakdown, enzymes mix with compounds and chemical reactions begin. It's exciting stuff!
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All of this produces flavour compounds. Processing such as rolling or simply turning the leaves can deliberately damage the leaf so as to enable oxidation to occur more evenly and at a quicker rate. This results in the linking of chemicals together to form compounds with even more flavour characteristics. It also allows the release of chemicals specifically created for the role of defence. These can be transformed into a wide array of aroma chemicals, that of course, also affect the flavour profile received by the brain. Next, fixing takes place stopping the enzymes in the leaf from any further reactions, but also breaking down the leaf’s chlorophyl to make further flavour compounds. Finally the leaf is shaped and dried. Flavour is still being created as the moisture content is brought down to around 3-5%, concentrating the chemicals.
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To examine the flavours associated with the six types of tea it is necessary to look for similarities between the processing methods and therefore the flavour compounds that are mostly found in them. In her book ‘Tea: a nerds’s eye view’ Virginia Utermohlen Lovelace MD does just this splitting them into three groups. These are green, yellow and dark and finally white, oolong and black. We will follow the same structure and endeavour to interweave our knowledge and experiences with more specific information from this book and other sources.
Green tea is quickly processed after plucking, with very little complexity. Key to the processing is the ‘fixing’ of the leaf by heat to prevent the enzymatic reaction that is oxidation. The leaf is left unchanged as possible and this in turn means little alteration of its chemistry. This gives a smaller and less varied range of flavour compounds than other types. The main factors in determining overall flavour are therefore the plant itself (variety and how it has grown) and the ‘fixing’ method used to stop oxidation (steaming and pan-firing).
Common in Japan, steaming the leaf at 100°C does not alter the chemical makeup majorly. Consequently this results in a grassy, vegetal and green flavour. One key compound that causes vegetal and often seaweed associations with Japanese green tea is one called dimethyl sulphide. This particular compound can also be found in asparagus and also broken down seaweed, hence the association. This aroma [seaweed & vegetal] is more prominent in teas with a high concentration of amino acids including high grade sencha and gyokuro [pictured below]
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Also prominent in Japanese green teas is the umami taste. This is created the proteins in the leaf is broken down into amino acids. One amino acid in particular, L-theanine, provides this umami taste as well as the usual sweetness. If you have heard the term umami but have no idea what this actually is then you can try this little experiment. Take around 5g of a steamed Japanese green tea (ideally gyokuro). Pour enough cold water to just cover the leaf and no more. Then simply leave this to infuse for at least 15 minutes before attempting to pour what little infused water into a sipping cup (you may have to squeeze the leaf a little). Then sip away and experience what umami is!
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Firing is more often used in China and involves contact with a heated surface. The temperatures achieved by this process can be much higher than steaming. This method has more of an affect on the chemistry of the leaf. One such change is the browning caused by the Maillard reaction. This provides the nutty and roasted flavours found in many types of tea, such as the green teas Long Jing (Dragowell) [pictured below] and gunpowder.
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Maillard ‘browning’ happens when sugars bind to specific amino acids and create golden-brown compounds in both colour and the rich malty, roasty flavours associated. This is what makes fried dumplings, baked bread, biscuits and toasted marshmallows so delicious. In tea amino acids and sugars are released during withering and also when damage to the leaf occurs, for example in rolling. The binding [of sugars to specific amino acids] occurs more quickly when the leaf is then heated to around 140-165°C. It can still occur at lower temperatures but just more slowly.
In tea L-theanine is the main amino acid involved in the Maillard reactions that occur. L-theanine is particularly prevalent in spring teas, due to its role in the increased growth at this time . This accounts for why many spring teas are so sought after for their flavour.
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A characteristic of some green teas (especially Japanese) is bitterness. Although caffeine is responsible for some of this, the main cause are the catechins. Green teas have more catechins than other types of tea as oxidation (which doesn’t occur in green tea) changes catechins to more complex polyphenols. Incidentally, shading the tea plant decreases the catechins produced which is why gyokuro is less bitter than those not shaded, for example sencha.
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Of course different people like different levels of bitterness. One method of counteracting this bitterness in tea is by adding sweetness. In Japan this can be offered in the form of wagashi, a sweet that often accompanies matcha. The ground nature of matcha means that its bitterness is stronger.
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Another method would be to add salt! From early drinking of tea this connection was known. The first tea text ‘The Classic of tea’ written by Lu Yu in fact recommended adding salt to the tea water. A way of experiencing this is to simply place a grain of salt on your tongue before you sip. Give it a go and head over to our IGTV to see this and the other earlier flavour experiment you can try at home!
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Yellow and Dark teas have a longer processing time, essentially starting off as green teas and then being fermented. However, compared with green teas, they actually don’t have much more of a variety of flavour compounds.
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YELLOW TEA
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Yellow tea, like green tea, is high in catechins, but a higher level of L-theanine mean that the overall flavour is more umami rich than bitter. The presence of L-theanine also means that when the fermentation releases simple sugars, they bind together resulting in the Maillard browning. This is where the toasty and nutty flavours come from.
Yellow tea also contains Dimethyl sulphide, as mentioned when examining green tea, which gives a seaweed, marine like flavour. There are also numerous compounds that contribute to citrus, floral and vegetal flavours, such as limonene, linalool, its oxides, β-Ionone and nonanal respectively.
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DARK TEAS
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Dark teas (including puer cha of Yunnan, liu bao cha from Guangxi, dark tea of Hunan, Old Green tea of Hubei) are enormously varied with regards to production methods and the microorganisms creating the fermentation. Even my favourite scientist Virginia Utermohlen Lovelace MD states ‘it is difficult to outline their chemistry in detail’.
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Looking at only Puer there are chemicals such as 3,7-dimethyl 1,5,7-octatrien-3-ol and Linalool oxide II which gives the mouldy, mushroomy, musty and earthy qualities more commonly associated with this tea. However there are also those that give green, citrus, floral, chocolatey and spicy flavours that often underlie these. One of these is β-Ionone mentioned earlier and associated with violet and lilac tones.
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Utermohlen goes on to state that the aging dark tea goes through halves the catechin content of the initial tea leaves as they are converted into ‘theabrownins’. This is what gives dark tea its extremely dark brewed colour.
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White, oolong and black teas are categorised together because oxidation takes part in all three, therefore developing flavours in the same way, albeit at different levels, with oxidation being promoted in oolong and black. White and black teas are actually similar in the quantities of varieties and concentration of aromas found. However, aroma compounds in oolongs are less concentrated but there are a greater variety found.
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WHITE
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White tea is plucked and then withered and dried. There is very little human interaction, but because withering can last up to three days the chemistry in this leaves or leaf buds changes a great deal. However it is usually characterised as light, sweet and floral.
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The lightness is down to low bitterness as catechin levels are lower than green teas. As mentioned previously trichomes are important in white teas, mostly bringing the floral and, along with some other compounds, hay like qualities. Linalool (as mentioned in yellow tea) is also present bringing more green, citrus and woodiness. There are also compounds that provide grassyness, whilst many bring floral aromas.
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OOLONG TEA
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Oolong (or wulong) teas are those that are partially oxidized. Oxidation in oolong tea can range from around 15% up to 80%, depending on the production method. This combined with where and how oolongs are grown means that its favour range is truly enormous.
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Part of this complexity is down to the plucking standard (what part of the plant is used), which can be up to 5 leaves. With each leaf down the plant β-Carotene and other carotenoids content increases. With processing these lead to the formation of many of the floral flavours mentioned previously.
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The complexity of the processing of oolong gives ample opportunity for flavour development. The leaf is sun withered as well as withered indoors, creating different stresses and therefore creates different compounds. Then the leaf is fired to stop oxidation, but crucially not to dry the leaf out completely, allowing for further flavour development to occur. The tea is then rolled and shaped into ribbon style strips or ball shapes, all the time allowing non-enzymatic oxidation to occur - developing flavours. Finally firing occurs to stabilise the tea. Even then the flavour development might not be finished, as some more oxidised oolongs are then baked for up to 18 hours. This effectively caramelises the sugars in the leaf amongst other reactions that create more toasty, sweet flavours.
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BLACK TEA
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Black tea is a fully oxidized tea. Once the leaves have been plucked they are withered for anything from 3–20 hours, before being rolled to promote oxidation. This provides a long period of time for flavour compounds to develop, but it also gives a lot of variation.
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Depending on how hard the withering is oxidation can take up to 5 hours for Indian-style black teas and up to 12 for Chinese. During this time to catechins are converted into larger molecules called theaflavin, thearubigen and theabrownin. Theaflavins give brewed tea a yellow colour as well as a brightness and astringency sometimes referred to as briskness. Thearubigins provide redness and a depth and body of flavour. Theabrownins (as mentioned earlier in puer) seem to be concerned with dark colours and don't add much flavour.
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Also during oxidation amino acids and sugars are freed meaning that Maillard browning occurs resulting in the nutty, roasty, sweet flavours. Another compound that has a large affect is methyl salicylate which has a strong flavour and a sweet aroma. During the next stage of fixing the heat required promotes more Maillard browning and also breaks down L-theanine to give caramel tones.
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We can't look at black teas without looking at bitterness and astringency. As mentioned in the last blog we noted that bitterness is a taste whereas astringency is all about mouthfeel. Astringency is the dry, puckering feeling often felt on the roof of the mouth and the tongue and is caused by the shrinking effect on the tissues caused by certain chemicals. As with bitterness this is desirable when in the right intensity. As mentioned earlier bitterness is created by catechins, which in black tea have been converted to theaflavin, thearubigen and theabrownin. This means there is actually less bitterness in black teas than green teas. The common misconception is that this would be the other way round, but this is mainly due to experiences with brewing smaller grade black teas for longer periods of time than they should - thus bringing more bitterness and astringency out.
Unfortunately (and also actually fortunately) all the flavours carefully constructed by the leaf itself and the producer do not just magically appear in the cup by just adding water. Brewing tea to release the flavour compounds is not always easy.
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With each tea we have to decide on four main factors. How much leaf? How much water? and what temperature it should be? How to long to brew? On top of these we of course have to choose our teaware and what method of brewing we should use. The merits and intricacies of these methods are beyond the scope of this blog, but all these elements combine to bring out the flavour of the tea in very different ways.
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Whilst the above is subjective and very personal one element is key to the brewing and that is the use of good water. Water usually makes up around 98% of the cup of tea and it can have dramatic affects on flavour. This will be covered in more detail in the future, but essentially water infuses the flavour compounds from the leaf. If the quality is not right you simply won't get the best possible cup and all that carefully forming of compounds will go to waste.
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The great thing is that with a bit of knowledge, an open mind and approach it is possible that you can make YOUR perfect brew. The emphasis is definitely on YOUR.
It is not surprising that with a system as intricate as that which we use to detect and process flavour and the complexities of the chemical makeup of tea mentioned above we don't all have the same experience from each sip.
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From nearly ten years of brewing tea for customers in our teahouses and doing countless tasting and sessions it is clear that we are all very different. The science backs this up!
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Over time mutations in the DNA concerned with taste receptors mean that some people lose functionality in this area. A fascinating fact quoted in 'Tea; a nerds eye view' is that more than 90% of East Asians carry a variant that means caffeine is less bitter. This drops to 75% of Europeans and between 10% and 30% of people from African descent.
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Another example from this book is that of β-Ionone that creates a violet floral aroma and is found in all teas. Apparently not everyone can smell it and this varies by population. 58% of Europeans, 35% of Han Chinese, 45% of Japanese and 77% of sub-Saharan Africans can smell it. Clearly this could provide very different reactions to the same tea, with nobody being wrong!
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And so to conclude. We hope that this second adventure into flavour has whetted your appetite for more. We know that this merely skirts the edges of a vast topic that we will continue to explore in the weeks and years to come. For us at Comins conversation and exchange of knowledge and ideas is central to our business so please leave messages, add, contest or simply say hi in the comments below. Let's keep talking! Whats next? Well coming out of this blog Rob has realised his interest in the topic of water so he will be following up on that in the weeks to come. Specifically around Flavour the last in our series will investigate the best way to taste tea - so stay tuned for that!
Thanks for reading!
References for this blog :
Huge thanks to many of our partners around the world who have, over the last 10 years help lay the foundational knowledge for this blog. Special thanks to KC who continues to open Michelles eyes to the wonderful word of tea chemistry every week.
Tales of the Tea Trade : Comins Tea
'Tea: A Nerd's Eye View' : Virginia Utermohlen Lovelace MD
Tea : A users guide : Tony Gebely
Chinese Tea Appreciation : www.sciencep.com
