Remove and discard the stems from the pineapples. Peel off the skins with a sharp knife and place in a large jug; refrigerate the pineapple flesh for later use.
Add the sugar and yeast to the jug with the skins. Cover with 1.5 liters/6.25 cups water and stir to dissolve the sugar and yeast. Cover with plastic wrap and leave in a warm place to ferment for 24 hours.
Line a strainer with cheesecloth and set over a large bowl. Strain the fermented pineapple mixture, discarding the peels and other solids. Refrigerate until chilled, or, if taking to a picnic, transfer to plastic bottles and freeze overnight and the cooler will defrost en route.
When ready to serve, cut the pineapple flesh into chunks. Add to the chilled cooler, along with the lemon slices and raspberries.