The soothing science of tea steeping

Today, we'll focus on true teas and how to steep them. Let's begin!

By Nik Sharma
February 9, 2021 2:01PM (UTC)
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(Bobbi Lin / Food52)

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In The Kitchen Scientist, The Flavor Equation author Nik Sharma breaks down the science of good food, from rinsing rice to salting coffee. Today: a piping hot cup of tea.

* * *

Every afternoon at 4 p.m., I partake in my daily ritual: tea with cookies (often gingersnaps) or a sandwich (usually cucumber, salted butter, and a sprinkling of black pepper). And if I'm stressed or on a tight deadline, my work table will without fail contain a cup of tea.

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True tea is produced from the leaves of the tea plant, also known as Camellia sinensis. This is regardless of whether it is black (Darjeeling), green (matcha), or white (white hair silver needle). After tea leaves are harvested, they're subjected to a process of drying, oxidation, fermentation, heating, and in some cases even smoking. Those are some of the steps that distinguish varieties like black and green.

Tisanes (aka herbals teas) are a separate category with a wide variety of fresh and dried ingredients — spices like ginger, herbs like peppermint, even fruits like mango — and a wide variety of steeping conditions.

Today, we'll focus on true teas and how to steep them. Let's begin!

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What's the difference between black, green and white teas?

Green tea is first treated to destroy the enzyme responsible for the darkening of the leaves. Moreover, the leaves do not pass through the withering or fermentation stages of production. As a result, green teas retain their green color.

The fermentation of tea leaves diminishes their grassy flavor profiles and creates fruity and floral notes, which gives black tea its noticeably stronger flavor.

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Some black teas, such as Keemun tea and lapsang souchong have a smoky flavor (though only the latter is smoked). Russian caravan tea is a blend of both Keemun and lapsang souchong teas along with oolong. These varieties carry a gorgeous aroma that makes them wonderful to steep in stocks.

Oolong teas lie somewhere between black and green teas. They're prepared by manipulating the oxidation conditions and, as a result, are partially oxidized and do not undergo complete fermentation. Because of the way oolong tea is manufactured, the flavor notes can vary from grassy to floral to fruity, and the color of the brewed tea can vary from shades of brown to green.

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In comparison to green and black teas, white teas are minimally processed and come from the younger, tender leaves of the tea plant that haven't yet opened and are still in their nascent bud form. This creates a more delicate flavor.

What gives tea its taste?

The bitter taste in tea comes from certain chemicals called polyphenols. In black tea, the major polyphenols are theaflavin and thearubigin, while in green tea the major polyphenols include epicatechin, epicatechin-3-gallate, epigallocatechin, and epigallocatechin-3-gallate.

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Theaflavin gives black teas their red color and is produced from the polymerization of  catechins through a series of chemical reactions during fermentation. Theaflavin is also responsible for mouthfeel and tea cream formation — this is considered an undesirable trait, referring to the white precipitate that forms as tea cools. Experimental studies on black tea have shown that calcium and glucose (sugar) in steeping water enhance the formation of complexes between caffeine, polyphenols, and theaflavin that form tea cream.

The stimulants in tea that keep us awake and alert — caffeine, theobromine, and theophylline — also contribute to bitterness. And some teas, like green tea, contain high concentrations of an amino acid called theanine, which contributes umami (you can use these teas to build savoriness in stocks and broths).

Sometimes dried fruit or herbs are combined with tea. Think of Earl Grey, which contains bergamot orange rinds or essential oils, lending a citrusy note.

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What are the grades of tea?

As "Food Chemistry" shares, there are several different grades of tea:

  • Leaf grade: Fully intact tea leaves, such as pekoe.
  • Broken tea: Broken or cut tea leaves; the preferred grade because there's more exposed area accessible to the water, leading to better tea extraction and a finer aroma.
  • Fannings and fluff: Broken or cut tea leaves typically used to make tea bags.
  • Tea dust: The tiny particles left behind from broken tea, which is used in tea bags.
  • Brick tea: Tea dust or ground tea that is compressed into a block. Historically, they were used as a form of currency by nomadic people of Mongolia and Siberia. Pieces of the compressed brick are broken and then steeped in hot water to produce tea.

What are the pros and cons of loose-leaf versus bagged tea? 

Loose-leaf teas are usually considered superior because the whole leaf is used, but they can be pricier than tea bags. Tea bags are more convenient, and since they contain either powdered or broken tea leaves, they're also generally less expensive. The bags are either made of some kind of natural paper or artificial material like plastic. Note: Plastic bags tend to release microscopic particles into the hot tea and are best avoided.

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How do you steep tea? 

Steeping is nothing more than extraction: tea leaves plus hot water. But the finer details — are the leaves placed in a strainer? For how long? And do other ingredients get involved? — depend on the type of tea and where it's being poured. In many countries, how tea is steeped is a cherished practice with specific traditions. In Japan, tea is steeped in hot water (the exact conditions vary by the type of tea). In India, chai is usually steeped in a pot of boiling water and then left to sit before milk is added.

How steeping is performed also affects the antioxidant properties of the tea. In one study, green teas appear to favor cold steeping, white teas prefer prolonged hot and cold steeping, and black teas do best in short hot water infusions.

You can steep tea directly in the water and strain it out with a fine-mesh strainer. Or place the leaves in a tea caddy or muslin bag, then immerse this in the hot water (the same way a tea bag works).

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Steeping conditions for common tea varieties 

This is meant to serve as a rough guide. Exact steeping conditions will vary by brand.

Does the water itself make a difference? 

Yes, the type of water can affect the final taste of your brew. Hard water, rich in metals like calcium, can affect the final taste and also produce the tea cream phenomenon mentioned above. Filtered tap water is usually the easiest, best option available to most of us.

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What's the ideal water temperature? 

The optimal temperature of the water is determined by the type of tea. Most brands state the target temperature and time on their packaging. The numbers might vary a little, but usually black teas are steeped at 185°F (85°C) and green teas at 170°F (77°C). If you want a higher boost from the caffeine in tea, steep it longer, for about 3 to 5 minutes. Usually, green and white teas are steeped at lower temperatures because, at higher temperatures, they run the risk of tasting bitter. In contrast, black teas are steeped at higher temperatures because they are a bit more robust.

How about timing? 

As the tea leaves soak in hot water, they rehydrate and their water-soluble components dissolve. The pigments in tea — tannins in black tea and chlorophyll in green tea — release their color, which they impart to the water. If you steep too long, beyond the recommended time by the manufacturer, the tea can taste very bitter.

When I make black tea with milk, I usually steep the tea leaves for two minutes, then add hot milk. If added earlier, the milk will prevent the tea from developing its rich, dark color and the flavor tends to be a bit milder. Non-dairy milk such as nut milks won't show this effect as dramatically because milk proteins tend to bind polyphenols (though some studies show that soy milk behaves similarly to dairy).

Is re-steeping a bad idea? 

I admittedly never do this, but you can. However, with every steep, the liquid will be less flavorful (and less caffeinated) than before. And there are some differences based on the tea: One study showed green tea to contain the highest level of antioxidant activity and total phenolic and flavonoid content when compared to black and oolong teas with every subsequent steeping performed. To help increase some of the flavor extracted, you can increase the temperature of the water used and even increase the amount of time it steeps; this works better with whole tea leaves — if tea leaves are already pulverized or broken (as in most tea bags), then the first steep usually extracts almost everything out.

What are some of your favorite teas to drink? Do you re-steep your tea — and if yes, how many times?

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