Approximate egothioneine ranking by concentration:
- Porcini/boletus mushrooms — typically among the highest
- Oyster mushrooms — very high
- Shiitake — high
- King oyster / maitake — high
- Common button/cremini/portobello — moderate
- Outside mushrooms: tempeh, black/red beans, oat bran, and some organ meats contain smaller amounts.
(Source: Gemini)

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