When it's hot, there's a certain amount of steam (3)

I believe the answer is:

tea

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'when it's hot there's a certain amount' is the definition.
I can't tell whether this defines the answer.

'of steam' is the wordplay.
'of' indicates the answer is hidden within the clue.
'TEA' can be found hidden inside 'steam'.

Can you help me to learn more?

(Other definitions for tea that I've seen before include "Hot infusion" , "Cha" , "grass" , "Hot drink" , "Refreshment" .)

I've seen this clue in the Evening Standard.

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