I was inspired to think and write about this topic by Amy of a girl with tea, who recently wrote a post titled Bad Mood = Bad Tea?
When people brew the same tea twice and end up with a radical different experience drinking it, those who are scientifically and mechanically minded often tend to look for explanations in terms of more objective and more easily quantifiable factors, such as water temperature, amount of leaf used, steeping time, and for the more nuanced among us, finer details of water quality or the type of vessel used to brew the tea. Yet another level of subtlety is to consider the size and shape of the vessel we drink from, which influences our perception of aroma as it changes how the smells rise from the cup, and also our perception of flavor as it can influence the heterogeneous distribution of various chemicals in different layers in the cup (for example, I notice that when drinking from a tall mug, certain flavors sink to the bottom of the cup).
But are these factors the biggest factors influencing our tasting experience? There are some teas where subtle differences in brewing temperature or steeping times can lead to major changes in how the tea tastes, but for the most part, the changes in taste affected by changes in these objective, external factors are relatively subtle. But there are some other factors that influence taste, and to find these, we need to look within, and at phenomena that are tougher to measure or pinpoint:
How does the state of our mind and body influence taste?
I've noticed that my taste perception is highly dependent not only on mood but on other factors within my own body. What I've eaten recently (even if the taste has long cleared my palate) and whether or not I'm hungry both influence my perception of taste in profound ways. My mood definitely influences my perception of taste, sometimes, like Amy pointed out, to the extreme of making a tea I would otherwise enjoy taste unpleasant or strange, if I'm in a bad mood. My mood is influenced by my environment and context, and especially, the company of whomever I'm with. I also notice that different teas taste different at different times of day.
There is actually solid science behind these seemingly crazy concepts. The Economist published an article a while back about how hormones influence perception of sweetness. Another article about taste published in The Independent explores how taste is influenced by factors as diverse as mood, hormones, lighting, association with various experiences, age, and genetics (and those are just a few of the topics touched on in that article).
There are many internal factors which influence taste, as well as external factors independent of the chemistry of the tea itself.
So, next time you wonder why a certain tea seems to taste different from the last time you brewed it, don't assume that this difference can be attributed to a difference in brewing. It may be your mood, hormones, company, the lighting, or some other factor that you can't even imagine.