I went through exactly this about 9 months ago. I couldn't find anything online about it, so I used a basic cider as the inspiration. Here are the exact notes I took while brewing it. Some sections were direct copies from the cider recipe, I added the rest.
1lb Munton’s Dry Malt
2Fl Oz Root Beer Concentrate
¾ cup priming sugar
5lbs granulated sugar
Hefeweisen Ale Yeast WLP300
- Pour 1 gallon of water in pot and bring to a boil. Add Dry Malt and stir.
- Dissolve the sugar in the heated juice. Stir frequently until the sugar is completely dissolved. Use a wooden or plastic spoon.
- Mix the liquid with the dissolved sugar into the bucket with the rest of the water, stirring thoroughly. Temp was at 79 degrees.
- Add yeast to the liquid in the bucket. Mix well.
- Put the lid on, tightly. Install the airlock and place the bucket somewhere out of the way, but with a steady temperature, usually around 70 degrees.
***After 1 day, bubbling stopped. I left it for another week with no change. Beer Nut rep suggested adding more yeast. WLP001 California Ale was added 1/23/10. I also picked up a hydrometer. Readings as follows:
5.5%, 11, 1.045 @ ~65 deg.
Root Beer was bitter tasting and ended with .5 grav after adding bottling sugar. I bottled half with only that sugar, then boiled 1/3 cup of sugar and threw that in with the other half. The mixture was very cloudy (looked like mud).
Unfortunately, my hydrometer broke before I could take the first reading, but I'll tell you that it was a very high alcohol content. The resulting drink was a bit like a sarsaparilla without a whole lot of sugar. However, my girlfriend and I drank it like crazy. It was odd, but good.
Changes I would make:
1) Only dissolve about half the original sugar at the start; add the rest when bottling (just have to make sure you let the CO2 work the O2 out of the bottles before capping so you don't get little beer bombs).
2) Wait to add flavor until bottling.
3) Start with California Yeast