Step 1

Simmer raspberries and sugar in water for about 20 -30 minutes

Step 2

Cool to room temperature and strain out raspberries

Step 3

Transfer what's now essentially sugary raspberry juice to a 2 quart glass ball jar or demijohn.

Step 4

Add whey and let it ferment for at least 3 days. Look for visible signs of fermentation via a slight fizziness. You can let it go longer for a less sweet soda as the bacteria will continue to feed on the sugars and convert them. Taste the soda as you go to get the sweetness you desire.