March 9, 2021

The science behind adding salt to coffee

Salt can be used for a lot of things – as many as 14,000, according to some estimates. We rely on it to season and preserve our food, to clean greasy surfaces, and to remove stains; some people even use it as an alternative to mouthwash

When it comes to coffee, salt has been used for an unusually long time in a number of cultures. Some have described it as an effective way to reduce bitterness and enhance desirable flavours for years.

However, not everyone is convinced of these benefits. Often it is not treated so much a flavour enhancer as it is a “hack” that makes lower quality coffee more palatable.

To learn more about the science behind adding salt to coffee, I spoke with two experts about bitterness, flavour perception, and how salt affects extraction. Read on to find out what they said.

You might also like our article on how grind size affects consistency and flavour.

Why do people add salt to coffee?

In cultures around the world, adding salt to coffee has been an established practice for decades.

For example, in Turkey, it’s traditional for the bride-to-be to prepare coffee with salt for her future husband and his family as a informal premarital ceremony. Similarly, “sea salt coffee”, consisting of salted milk foam atop an iced americano, is a popular beverage in Taiwan. 

In Northern Scandinavia, consumers have added salt to brewed coffee for decades. And finally, brackish water with high salt content is often used to make coffee in coastal areas of Europe.

But why do people choose to do this?

Sara Marquart is the Head of Flavour at The Coffee Excellence Center, a leading public science, technology, and innovation centre. She tells me that adding salt is a great way to balance the flavour profile of bitter robustas and coffees with very dark roast profiles.

“The addition of salt in coffee dampens bitterness without using other additives,” she says. “Salt naturally brings out the sweetness of coffee and maintains pleasant aromas. If people are sensitive to bitterness, even in specialty coffee, adding salt is a good alternative to using milk and sugar.”

In 2009, food science expert Alton Brown suggested adding salt to coffee in an episode of his cooking show Good Eats. He said that for every cup of water and two teaspoons of ground coffee, you should add half a teaspoon of salt to neutralise the bitterness of the coffee. 

“Not only does salt cut the bitterness, it also smooths out the ‘stale’ taste of tank-stored water. Research has proven that salt is actually better at neutralizing bitterness than sugar,” he said.

Although Brown wasn’t the first to put salt in coffee, he drew widespread attention to the technique. Today, some even coffee drinkers know it as “the Alton Brown Trick”.

The science behind salt and bitterness

While a small percentage of the bitterness in coffee comes from caffeine, the majority is generated by two compounds: chlorogenic acid lactones and phenylindanes. 

These compounds are actually not inherently present in green coffee. Instead, they are released when coffee is roasted as chlorogenic acids are broken down.

Phenylindanes create the perception of bitterness and are linked to the length of the roast. The darker the roast, the more phenylindanes there will be.

However, bitterness is also influenced by extraction. A lack of precision when brewing coffee, such as letting coffee sit in a French press for too long, using water that is too hot, or choosing the wrong grind size can all lead to overextraction. This causes coffee to take on an intense, bitter flavour in the cup.

“The majority of bitter tastants are more evident in overextracted coffee beverages,” Sara explains. “They taste harsher and more bitter than usual.”

Our taste buds enable us to identify sweet, sour, salty, bitter, and umami flavours, but our biological reactions to bitterness differ from other tastes. When we eat or drink something bitter, calcium ions are sent to our brain. And while salt can enhance sweet, sour, and umami flavours, it tends to reduce our perception of bitterness.

“Bitter tastants activate our bitter taste receptors, signalling to our brain that we consumed something bitter,” Sara says. “Salt, and more precisely, sodium ions, activate salt receptors on our palate.”

Sodium ions bond to the salt receptors on the tongue, inhibiting our perception of bitterness to balance flavours.

“When the bitter receptor and salt receptor are activated at the same time, it can lead to [something called] ‘cross-modal perception’. This suppresses the bitter taste, and increases other taste senses, such as sweetness,” Sara explains.

This means that when you add salt, the sweetness in coffee is naturally enhanced. This is why salt is often added to the rim of the glass for margaritas; it brings out the sweetness in the lime and the tequila.

What’s the best way to add salt to coffee?

Two of the big questions around adding salt to coffee are when you should do it and how much you should use. While Sara suggests adding salt to your coffee grounds before you brew, not everyone agrees.

David Jameson is Head of Coffee and Sustainability at Bewley’s Tea and Coffee. He tells me that whenever he’s added salt to coffee, it has always been the final stage, into a brewed cup.

“It’s much easier to control dosage this way,” David says. “It might be advisable to pull a shot, or prepare a drip coffee first, assess its bitterness, and then start adding salt, increasing the amount until the perfect taste profile is achieved.” 

The approach put forward by coffee consultant and World Barista Champion James Hoffmann goes even further. Rather than adding salt crystals directly to brewed coffee, Hoffmann created a solution with a fixed salt concentration that can be dripped into the coffee. 

He found that adding 0.3g of a saline solution with 20% concentration noticeably improved the taste and mouthfeel of a low-quality instant coffee.

“A pinch of salt (around 0.5g of salt for a 1L brew) could increase the sweetness of coffee subtly and decrease the bitterness at the same time,” Sara says. 

Meanwhile, coffee roasting expert Scott Rao found that 0.15g of salt per 100g of brewed coffee yielded the best tasting results, for both espresso and filter.

When shouldn’t you add salt?

Those who add salt to coffee often see it as a highly effective way of reducing bitterness and enhancing sweeter flavours. However, it’s important to note that this doesn’t always produce the best results.

David tells me that although he has first-hand experience of the benefits of salt in coffee, it’s more important to focus on the quality of the beans you use.

“In December 2015, I won the UK Coffee in Good Spirits Championship using a Catuai from Graciano Cruz’s world-renowned Los Lajones farm in Boquete, Panama,” David says. 

“I used a couple of drops of a salt solution. This enabled the judges to better appreciate the complexity of the acidity, enhanced the sweetness, and balanced the bitterness.

“Having said that, would I automatically add salt to my rare, fine Yemeni auction lot? No, probably not. 

“If you are seeking to improve bad tasting coffee, adding salt can be helpful, but ultimately, using higher quality beans is the best way to improve the flavours in the cup.”

It’s important to note that for higher quality specialty coffee, salt can obscure the delicate and nuanced flavours that set the coffee apart.

Much like adding milk, cream or sugar, adding salt to more complex coffees will make it more difficult to determine subtle flavour notes or acidity in the cup.

“One of the pleasures of coffee is that when it’s good it has the right kind of bitterness,” Hoffmann says in his video. “When it’s balanced out by sweetness and acidity, some bitterness is very pleasant.”

While salt can enhance sweeter flavours and balance out bitterness in the cup, brewers experimenting with it need to be careful. Like adding milk, cream, or sugar, salt can mask the distinct characteristics of higher quality coffees, masking the uniqueness or delicate complexity of a cup.

Salt is useful for masking or balancing the harsher flavours of lower quality coffee or darker roasts than bringing out the sweetness in a light roast, for example. However, the only way to find out what you like is to experiment. Next time you brew a cup of coffee, why not try adding a pinch of salt and see what you think?

Enjoyed this? Then read our guide to dialling in espresso.

Photo credits: Sara Marquart

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