What Makes Sweets Sour?

Sourness in sweets is not a flavour in the way strawberry is. It is an acid, and which acid a manufacturer chooses changes the whole experience of eating the sweet.

The three acids

• Citric acid — from citrus fruit. A clean, sharp sourness that arrives fast and fades fast. The most common by a distance.
• Malic acid — from apples. Slower to arrive and lasts noticeably longer, which is why the really punishing sour sweets use it.
• Tartaric acid — from grapes. The sharpest immediate hit of the three.

The extreme sour sweets work by coating the outside in acid crystals, so you get the entire dose the moment it touches your tongue rather than gradually as it dissolves.

Sour and fizzy are different things

Sour is acid alone. Fizzy adds sodium bicarbonate to the coating. When saliva wets it, the acid and the bicarbonate react and release carbon dioxide — that is the tingle, and it is the same reaction that makes a cake rise. A sweet can be sour without being fizzy, but almost nothing is fizzy without also being sour, because you need the acid for the reaction.

Sherbet is the same trick

Sherbet powder is acid and bicarbonate sitting dry next to each other, doing nothing at all until they get wet. That is why a dip dab is inert in the packet and fizzes on your tongue. More on that in our sherbet range.

Do sour sweets damage your teeth?

The acid can soften tooth enamel temporarily — this is about the acid rather than the sugar, and it is why sugar free sour sweets are not exempt. The standard dental advice is to rinse with water afterwards and wait about thirty minutes before brushing, because brushing softened enamel does more harm than leaving it. Enamel re-hardens on its own within an hour or so.

Why some sour sweets fade and others do not

It comes down to how soluble the acid is and where it sits. An acid dusted on the outside dissolves in seconds, so the sourness is a hit that disappears. An acid worked through the body of the sweet is released gradually as it dissolves, so it lasts but never spikes. The genuinely punishing sweets do both: an acid coating for the initial assault and malic acid in the centre to keep it going.

The acids, by how long they last

• Tartaric acid — sharpest immediate hit, fades fastest.
• Citric acid — clean and bright, moderate duration. By far the most common.
• Malic acid — slower to arrive, lasts noticeably longer. The one used when a manufacturer wants a sweet to be a challenge.
• Lactic acid — softer and rounder, used to smooth the others out rather than on its own.

Enamel, properly explained

Tooth enamel starts to demineralise below about pH 5.5. Sour sweets sit well under that, so they soften enamel while you are eating them. The enamel remineralises on its own from minerals in saliva, but that takes roughly thirty to sixty minutes.

This is why the standard dental advice is to rinse with water and wait about half an hour before brushing. Brushing softened enamel physically removes it, which is worse than not brushing at all. It also means sugar free sour sweets are not exempt — the erosion is caused by the acid, not the sugar. Sugar free helps with decay, not with erosion.

Eating them with a meal rather than grazing across an afternoon reduces the number of separate acid attacks, which matters more than the total amount.

The four acids, and what each one does

Sourness is not one flavour. Different acids hit at different speeds and fade at different
rates, which is why one sour sweet is a slap and another is a slow burn.

• Citric acid — the common one. Sharp, immediate, and gone quickly. From
  citrus originally, now made by fermentation.
• Malic acid — the apple one. Slower to arrive and it lingers noticeably
  longer, which is why it is used where a sustained sourness is wanted.
• Tartaric acid — from grapes. The harshest of the group, and the one that
  does most of the work in the really aggressive sours.
• Lactic acid — softer, rounder, less of a spike. Used to fill out a sour
  profile rather than to lead it.

Most manufacturers blend two or three so the sourness has an arc rather than a single peak.

Why the sour is on the outside

The acid is dusted or sprayed onto the surface after the sweet is made, not mixed through it.
There are two reasons. Acid interferes with setting — it inverts sugar and can stop a gel
forming properly — and a coating puts all the sourness in direct contact with your tongue at
once, which is the whole effect.

It also explains the practical problem with them: acid coatings are hygroscopic.
They pull moisture out of the air, which is why unwrapped fizzy and sour sweets go tacky and weld
together within a day or two of being opened, and why they are the wrong choice for party bags made
in advance. Our sweet cone guide covers
which lines survive being made ahead.

Fizzy is a different thing entirely

People use “sour” and “fizzy” interchangeably and they are not the same mechanism. The fizz is
sodium bicarbonate reacting with the acid in the moisture of your mouth, producing
carbon dioxide. That is the same reaction as sherbet, and it is a physical sensation rather than a
taste.

A sweet can be sour without being fizzy, fizzy without being especially sour, or both.

Does it damage your teeth?

Yes, and by a different route from sugar. Sugar feeds bacteria that produce acid; a sour sweet
applies the acid directly, with no bacteria involved. That means even a sugar-free
sour sweet can erode enamel.

The damage looks different too — smooth, glossy thinning rather than cavities. Two
practical points: do not brush straight afterwards, because softened enamel scrubs away, and rinse
with water instead. More on the mechanism in
are mints good for your teeth?

Shop fizzy and sour sweets and
sherbet.