Olive Leaf Tea

http://www.oleaft.com/olive-leaf-tea/

Making the Perfect Cup of Olive Leaf Tea:

It is important to begin with a good quality clean water. Boil the desired quantity of water and let it cool slightly before pouring over the leaves, to prevent burning them. This helps the taste and avoids damaging the phytochemicals. If you like, you may also flavour your olive leaf tea with any of the following complimentary additions and herbs: Honey, Lemon, Milk, Cinnamon, Rose Petals, Peppermint, or Lavender Flowers.

http://www.oliveoilemporium.com/HealthBenefits/OliveLeafTea.aspx

Bring to a boil then reduce heat to let the water cool to approximately 185 degrees (212 is boiling). Too hot water will "burn" olive leaf lowering the antioxidant polyphenol count while creating a bitter flavor. Allow olive leaf to steep 3-8 minutes depending on the strength you desire.

http://www.olivus.com/preparation_olive_leaf.htm

ps. I assume the same goes for Rosehip Tea, also extremely rich (if not the most) in vitamin C, which does not tolerate heat well.