This is the "old school" yeast recipe from the Hires extract bottle. They now make a "Big H" variety, but the recipe on the bottle is for the dry ice version. This was my favorite summer drink growing up.
Pour extract over 4 lbs of sugar. Mix well. (Vary amounts of sugar and extract to taste).
Dissolve mixture in 4 3/4 gallons of lukewarm water.
Mix 1/2 tsp of dry active yeast in a pint of lukewarm water. Allow to stand 5 minutes. Stir well and strain through cheesecloth. In cool weather (under 70F) double the amount of yeast used. In hot weather (over 90F) cut the amount in half.
Add the yeast mixture to the solution of sugar, extract, and water. Mix well and pour into sterilized bottles immediately. Fill bottles to within 1/2 inch of the top to minimize spoilage caused by excess air. Cork bottles securely or seal with crown or stopper.
Place bottles on their sides in warm place(70-80) until effervescent. (If set in a cool place immediately the beverage will sour and remain flat.) The product should be ready to drink in about 5 days (longer in cooler weather.) Move the bottles to a cool place. Refrigerate just before drinking. The beverage will have a slight yeast flavor and contain some sediment. Do not filter.
For best results - use only returnable type carbonated beverage bottles.