Remove the stems from the pineapples and discard.
Peel off the skins with a sharp knife and keep the pineapple flesh in the fridge until needed.
Place the pineapple skin in a large jug with the yeast and sugar.
Cover with water and stir continuously to dissolve the sugar and yeast.
Cover the jug with cling and leave in a warm place to ferment for 24 hours.
Strain the fermented pineapple mixture through a clean muslin cloth placed inside a strainer.
Discard the pineapple peels and other solids.
Either chill in the fridge until needed or if taking to a picnic transfer to plastic bottles and place in freezer to freeze overnight. Take to picnic frozen and they’ll defrost en route.
When ready to serve cut the pineapple flesh into chunks and add to the chilled cooler along with the lemon slices and raspberries.