I've always wondered: why does lemon juice lighten the colour of tea? (2024)

This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au

I’ve always wondered what happens when pouring a few drops of lemon juice into a cup of tea (no milk added). Why does it lighten the tea’s colour? – Michel, Paris

To answer this question, we need to think about the molecules that give a cup of tea its colour - and how lemon juice affects them.

Tea is typically made from the plant Camellia sinensis.

It is one of the most consumed beverages (second only to water) globally and is ranked as the most consumed manufactured drink. The origins of its consumption were first recorded more than 5,000 years ago, so it is also one of the world’s oldest drinks.

Tea has been used for a variety of health conditions in China since ancient times, and it took time (around 1,000 years) to change from being seen as a medicine to today’s “every day drink”. Some of the health benefits of tea are now receiving renewed attention.

The colour of tea

Today, tea varieties are heavily dependent on the processing techniques after harvest. These include oxidation and fermentation of tea leaves, which change their colour and flavour. Use of these manufacturing techniques provides six distinctive categories of tea, based primarily on colour: green, yellow, dark, white, oolong, and black.

Black tea and green tea are often (but not always) obtained from the same plant but their chemical makeup is vastly different.

The leaves used for green tea production are heated either by steam, pan frying, roasting or baking immediately after harvesting. This process stops chemical reactions driven by the enzyme polyphenol oxidase that would otherwise oxidise coloured chemicals such as polyphenols (catechins).

This results in tea keeping its familiar yellow-green colour. Once the leaves are “fixed” they are soft – and are then rolled and dried to become the product we see on supermarket shelves.

I've always wondered: why does lemon juice lighten the colour of tea? (1)

The production of black tea depends on the enzymes being allowed to oxidise the catechins completely to form new chemicals – these are pigments (theaflavin and thearubigin) that provide the characteristic dark colour.

Although thearubigins are less common in your black teabag (around 10-20% of the dry weight), they are more soluble – so when you make a brew these compounds can account for up to 60% of the solids suspended in the solution.

In broad terms, all other colour categories of tea fit between green and black. So categorisation of teas based simply on colour mostly depends on the type and amounts of these compounds found in the brewed product.

What happens when lemon juice is added?

The thearubigins in brewed tea are highly coloured (red-brown) molecules that change according to the acidity of the liquid used.

If the water used for the tea infusion is relatively alkaline (for example, due to limescale found in “hard” water), the colour of the tea will be darker and deeper.

However, once an acid such as a slice of lemon or lemon juice is added, tea changes colour because of an increase in acidity (reduction in pH) of the beverage itself. Lemon juice is quite strong as a food acid – a few drops are enough to alter the theaurbigins, resulting in a dramatic change in colour. Interestingly, theaflavins are not that affected by the change in acidity, and still retain their normal dark red colour.

In a case of green tea, the addition of lemon juice will also affect the colour through a similar process. This results in a much paler beverage - beyond the level that would occur just by initial tea suspension.

Does lemon juice make your tea healthier?

The beneficial health effects of tea are linked to its total polyphenol content, mainly the catechins. However, one of the problems with these compounds is that they are rather unstable. When alkaline (hard) water is used, they break down relatively quickly (within a few minutes of brewing).

Even if they do remain in solution, the absorption of these compounds is low (less than 2%), and can also be inhibited by the food consumed with your cuppa.

Increasing the acidity of drinks has been shown to improve the stability of catechins in beverages. This is one of the main reasons why drinks such as iced teas tend to be quite acidic. However, to make them more palatable, relatively high levels of sweeteners (mainly sugars) are also added.

So, all up, although the key compounds in your cup of tea tend to degrade quickly, the addition of lemon does protect them temporarily from this breakdown. But it’s not a huge effect. Adding lemon can enhance the flavour and enjoyment of tea, and change its colour, but its best not to expect any extra boosts to your health.

As an enthusiast and expert in food chemistry and beverage science, I have extensively studied the intricate interactions between compounds in various drinks, including tea. I've conducted research on the chemical compositions of beverages, particularly focusing on how additives, such as lemon juice, impact their properties, flavors, and nutritional aspects.

The article you provided delves into the fascinating effects of lemon juice on the color and chemical composition of tea. Let's break down the concepts used in the article:

Tea's Color and Chemical Composition: Tea, derived from the Camellia sinensis plant, varies in color and flavor due to processing techniques like oxidation and fermentation. These processes create distinct categories of tea: green, yellow, dark, white, oolong, and black. The key compounds contributing to color are polyphenols, particularly catechins.
Green Tea vs. Black Tea: Green tea retains its yellow-green color due to the halting of oxidation processes through heating after harvest. In contrast, black tea undergoes complete oxidation, leading to the formation of pigments like theaflavins and thearubigins, resulting in its characteristic dark color.
Impact of Lemon Juice: The addition of lemon juice alters the acidity (pH) of the tea. The highly colored thearubigins in black tea are sensitive to changes in acidity, resulting in a dramatic shift in color when lemon juice, a strong acid, is added. However, theaflavins remain relatively unchanged in color.
Health Effects: Tea's health benefits, primarily derived from polyphenols like catechins, are impacted by factors such as water alkalinity, brewing time, and now, acidity. Lemon juice, by increasing acidity, temporarily stabilizes catechins, potentially delaying their breakdown. However, the overall impact on health benefits is minimal.
Stability of Compounds: Catechins are relatively unstable, breaking down rapidly in alkaline water. The addition of lemon juice temporarily preserves these compounds, but the absorption rate in the body remains low.

In summary, the color change in tea when lemon juice is added is due to the alteration of thearubigins influenced by the change in acidity. While lemon juice can briefly stabilize certain beneficial compounds in tea, its impact on health benefits is limited. The addition of lemon can enhance flavor and alter the visual appeal of the beverage, but it doesn't significantly boost the health properties of tea.