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HMRC internal manual

VAT Food

Items benefiting from the relief: what is food?: food ingredients and additives: flavour enhancers

These are not flavourings, but substances that make existing flavours in the food seem stronger. They are therefore not essential to the finished food product, and so are liable to VAT at the standard rate. The commonest example is monosodium glutamate. Barbecue flavour enhancers such as hickory chips, are similarly not regarded as food (nor as a fuel) and are standard-rated.