The impact of sodium on coffee flavour

Sodium

Sodium is quite easy to understand compared to the other metal ions – because we have taste receptors that directly interact with sodium, and it directly gives us the taste of saltiness.

Potassium interacts in a similar way, but gives a less strong salty sensation.

What effect does it have on taste?

Interestingly, sodium is also known to decrease bitterness sensations from other compounds – so high levels of sodium are useful to reduce the bitterness of coffee.

However, this does come with the perception of saltiness, so it can be a trade off.

In our experience, anything above about 0.5 mM or ~11.5 mg/L starts to bring an obvious saltiness that might be displeasing. But, it depends on the person and the coffee, naturally.

Interestingly, sodium is able to depress the bitterness of calcium chloride solutions, but not magnesium sulfate – which further suggests that magnesium and calcium affect our taste by other means.

Though, at the concentrations you'll use, the main bitterness is from the coffee – not the added magnesium/calcium (thankfully).

Potassium

Potassium behaves much like sodium, giving a salty taste.

This saltiness is less pronounced – being about half that of sodium (if simply comparing sodium and potassium chloride).

However, potassium does not decrease bitterness in the same way sodium does.

For this reason, high levels of potassium should be avoided, since the saltiness doesn't come with much benefit, and can add more bitter flavours than sodium chloride.

Potassium salts can be used to adjust water much like sodium and can be useful when you need a soluble source of bicarbonate/citrate, but want to avoid salty taste – as a mixture of 0.5 mM Na+ and 0.5 mM K+ will taste less salty than a mixture of 1 mM Na+.