The amazing Netflix documentary series, The Last Dance, tells of the incredible basketball career of Michael Jordan and the Chicago Bulls. If you’re looking for a dunk in basketball terms, I suggest you watch it. Here we’re going to talk about tea and biscuits, sorry basketball fans. Tea lovers, you’re going to want to fetch the biscuit tin for this one…
I don’t know about you, but working from home and writing my thesis has led to an awful lot of tea drinking and biscuit dunking. We British LOVE a cup of tea, drinking upwards of 165 million cups a day (enough to fill 20 Olympic swimming pools). If you want to learn more about the history of tea follow this LINK. Whilst tea varies depending on where in the world it originated, chemistry plays a large role in the types of tea, influenced by environment, cultivation, weather and processing. “No food material is more fascinating and chemically diverse and complex [than tea]” says Nikolai Kuhnert, professor of chemistry at Jacobs University Bremen, “tea is the ultimate mystery…to food and analytical chemists”.
Tea leaves are packed with compounds, minerals, vitamins, caffeine, more than 700 aroma compounds, and the main component, polyphenols (or tannins). Tannins largely provide the dry mouth feeling (astringency), as well as colour and flavour; a strong cup of tea can hold 240mg of tannins. Amongst the other compounds in tea, flavinoids are the most important group (some of which are studied for health benefits). Of these, theaflavins and thearubigins (which are formed during tea processing) also give tea flavour and colour, whilst theobromine (which is also found in chocolate) contributes to the bitter taste of tea. Most interestingly, tea is both a stimulant (caused by caffeine) and a relaxant (caused by theanine), which reduces mental anxiety and increases our sense of wellbeing by increasing gamma-amino butyric acid (GABA) production and promoting alpha brainwave activity. GABA inhibits (blocks) chemical messages in the brain, decreasing nervous system activity, whilst alpha brainwaves are dominant in a resting state of the brain. (That’s why I find sitting down with a cuppa so calming…)
How do you make the perfect cup of tea? Whilst everyone will have their own preference (mine is a dash of milk and one sugar please), science can help us make the best possible cup for the type of tea leaf used. There are 3 primary points to consider: water type (soft water leads to a cleaner finish whilst hard water creates a scummy layer), temperature, and steeping time. Different teas need different brewing temperatures (there are 6 teas types: white, yellow, green, oolong, black and post-fermented) and steeping time effects taste too. The rate at which tannins, amino acids, and aroma flavours diffuse into the water depends on tea type and water temperature. The longer the steeping time, the more tannins are released producing a rich flavour, but too long and you get a bitter taste. If the water is too hot, this also leads to tannins and other flavour compounds dissolving too quickly, making an imbalanced brew, whilst too little heat means a weak, flavourless cup. Darker, stronger teas (e.g. black, oolong etc.) need higher temperatures and longer steeping times compared to lighter teas (e.g. white, green etc.). Loose leaf tea is a bit of a luxury though, as most of us (96%) opt for ease with teabags. A teabag has limited space for diffusion of compounds (i.e. the leaves can’t expand and release compounds) making for a less diverse flavour profile. The leaf pieces are smaller in a teabag too, meaning they have a greater surface area exposed to light and oxygen, which affects flavour as aromatic oils are vulnerable to evaporation. Basically, if you want a flavourful cuppa get some proper leaves and a teapot!
What about the dunk? I would find it incredibly difficult to pick a favourite biscuit to have with a cuppa, but I could probably narrow it down to bourbons, chocolate digestives/hobnobs and sometimes an all butter shortbread, but what makes the best biscuit for dunking? There is in fact scientific proof that dunking biscuits in tea makes them taste better. 10 times more aroma compounds are released when a biscuit is dunked as heat causes them to diffuse out, making the biscuit taste better. But what makes the perfect dunk? There is nothing more upsetting than seeing the biscuit you have waited for break off into your tea. Fear no more, Len Fisher devised a formula for biscuit dunking in 1998, balancing the race between sugar dissolving and your biscuit falling apart. In fact, they found the optimal way to dunk a chocolate digestive was actually horizontally, biscuit side down, but I’m not sure I’ll be changing my more practical vertical method anytime soon. If you want to see how long various biscuits last, check out the video below (is a fig roll a biscuit?) and this LINK will show you the recommended dunking time of each.
If you want to try a dunking experiment at home (a great one for kids) try this LINK, and if this post hasn’t made you want tea and biscuits, you must be a coffee lover. There’s nothing I can do to help that, but I can teach you about the science of coffee HERE instead.