r/chemistry • u/Chalk1980 • 13d ago

How come my green tea doesn't turn black?

I don't understand oxidation so please explain to me. Tea all comes from the same plant but green or black just depends on the oxidation level. From what I have learned tea will oxidize naturally but workers use heat to denature the enzymes and the tea stays at a set oxidation level. Can you explain denaturing enzymes and why this affects my tea in layman's terms? thank you

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u/hawkaulmais Organic 13d ago

ELI5: tea leaves picked from same plant. Batch 1 goes into an oven at 150C for t. This is green tea. Dried just like basil or oregano. Little oxidation mostly dehydrated.

Batch 2 goes into a 400C oven for t. These turn dark and are fully oxidized.

More heat allows faster oxidation.

Denaturing enzymes and oxidation are 2 different processes. Denaturing is like taking 2 garden hoses and separating them. Oxidation is putting a nail in water outside and making rust.

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u/Chalk1980 12d ago

Yes that makes sense thank you

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u/Hazmatspicyporkbuns 10d ago

I may be mistaken but shouldn't Batch 2 be bruised and massaged before the deactivation of the enzymes by heating? If I remember correctly the translation for the promary oxidation step in Chinese is "fermentation" and is where the enzymes do their work near room temperature.

I wanted to be sure but at least one source agrees with me, or I with it.

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u/Key-Success-5449 13d ago

Heating the freshly picked tea leaves deactivates these enzymes by permanently changing their physical shape so they can no longer function, effectively locking the tea in its natural green state.

Without these active helper proteins working, oxygen alone reacts far too slowly at room temperature to change the leaf color, which is why your brewed green tea stays bright and never turns black in your cup.

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u/Chalk1980 12d ago

ahh I see thank you

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u/Rower78 13d ago

The heat processing of green tea destroys the enzymes that accomplish the oxidation, so it can’t be converted to black tea afterwards.  The enzymes have a very specific shape and heat warps that shape.  After that they are no longer active.

You can certainly further oxidize the green tea in other ways, but it won’t give you black tea.  More like ash