Finely chop the shallot and place it in a small saucepan with the karamu berries.
Bruise the Karamu berries and Shallot together using the back of a metal spoon (Do not use a wooden utensils as it will soak up the juice and become discoloured)
Add the water, vinegar, salt and sugar to the saucepan. Stir to combine the bring the ingredients up to a boil, then immediately remove the saucepan from the heat and allow the ingredients to steep together for 10 minutes.
Strain mixture through a fine mesh sieve into a clean bowl. Add the versawhip and xanthan gum powder to the mixture and blend together with a stick blender at a high speed for 30 seconds then place in the refrigerator to completely cool. This is your foam base.
To Serve: Whip the foam base using a kitchen mixer fitted with a whisk attachment for 2-3 minutes at a high speed. The foam is ready when it is able to hold a stiff peak. Place a generous teaspoon of foam onto each oyster. Garnish with some deseeded Karamu berries if you have some spare. Service immediately.