How Hot Should Water Be For Coffee

In the UK, we consume approximately 95 million cups of coffee and 100 million cups of tea per day. We all have our idiosyncrasies when it comes to preparing our favourite brew, and we all believe, deep down, that nobody really knows as well as we do how to make the perfect cuppa.

But when it comes to water temperature, there might, possibly, be room for improvement …

Optimum water temperature for tea

It’s generally acknowledged, among professional tea manufacturers, that you should not pour boiling water onto tea. (Many of us, of course, do just that.) How hot, then, should the water be?

The optimum water temperature varies according to the type of tea you’re making. And the type of tea depends on the extent to which the tea leaves have been oxidised.

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Oxidation

All teas are the dried leaves of Camellia sinensis. The difference between white, yellow, green, oolong, and black tea lies in the degree of oxidation. Green tea, for example, is hardly oxidised at all, while black tea is almost fully oxidised.

Like many plant species, Camellia sinensis contains polyphenols – a group of organic compounds that includes catechins (deterrent to predators) and tannins (regulation of the plant’s growth and ripening). Through the process of oxidation – catalysed by polyphenol oxidase, an enzyme that occurs naturally in the tea plant – catechins are converted to other types of polyphenols called theaflavins and thearubigins. These chemical compounds give black tea its colour, comparable to the browning of apple flesh, which oxidises when exposed to air.

Oxidation (loss of an electron) is one half of a redox reaction. The other half of the reaction (the gaining of an electron) is reduction. In the case of tea, the oxidising agent – i.e. the chemical that’s being reduced – is oxygen. Although the term “oxidation” comes from “oxygen”, a redox reaction doesn’t always involve oxygen.

Green tea is an excellent antioxidant because the catechins in the tea are available for oxidation in the body. By donating an electron to an unstable chemical (free radical), catechins can interrupt the chain redox reaction that’s associated with ageing.

How hot should the water be for a cup of tea?

Water that’s too hot will scald the tealeaves, giving the tea a bitter taste. The greater the extent of oxidation, though, the better the tea can withstand high temperatures. If the water’s too cool, the tea’s flavours won’t fully infuse the water.

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So, here’s a rough guide to the optimum water temperature for the various types of tea:

  • Black tea (intense oxidation): 95°C
  • Oolong tea (partial oxidation): 85°C
  • Yellow tea (partial, slow oxidation): 80°C
  • Green tea & white tea (minimal oxidation): 80°C
Optimum water temperature for coffee

There are approximately 120 species in the genus Coffea, but only a few of these species are cultivated for their caffeine-rich seeds, which are roasted, ground, and infused in hot water to produce one of our favourite drinks.

Two species account for roughly 99% of the world’s cultivated coffee. Coffea canephora is best known as robusta, which is the name of one of the two C canephora varieties. Coffea arabica is a hybrid of C canephore and C eugenioides.

There are several ways of brewing coffee:

  • Espresso is a brew of coffee made by forcing a small amount of hot water, at high pressure, through finely ground coffee. Containing a lot of the coffee’s oily solids, espresso is full-bodied and flavoursome. Espresso can be consumed as it is or topped up with hot water or milk.
  • Filter coffee is brewed slowly. Hot water drips through the coffee grinds, and much of the coffee’s oils are lost to the paper filter. Many people prefer the plainer taste of filter coffee.
  • French-press coffee is steeped in hot water and then filtered by a metal filter which lets through the oily solids. Like espresso, it has a full-bodied flavour.
  • Freeze-dried (instant) coffee is dissolved in hot water.

There are three main variables in coffee brewing: 1. time; 2. grind; 3. temperature. Here, we’re concerned with temperature.

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Water that’s too cool will fail to extract the coffee’s flavours, whereas water that’s too hot will over-extract, producing a bitter brew. The optimum temperature for coffee is 95°C.