What is the method for adding anything to mead without infecting it?

[tenchu_11]

Wether it's habiscus, fuit, spices or hops what is the most proven safe method. Should i boil the thing i wish to add and add it after it cools down to make sure its sanatized by being boiled (i will also of course wash fruit and such). Or putting it into the mead after it has fermented and alcohol content is at a certain level?

 

[Southside]

I just wash all my berries then freeze them, thaw them, refreeze and thaw them again (this helps break down the cell walls) and then mash them & just drop them in, then a quick blast of CO2 . I've found that high ABV kills everything. I have never had an infected batch. I usually add mine with little to no fermentation going on.