First, ferment the serrano peppers. Roughly chop the peppers, then pack them into a ball jar, leaving at least 1 inch of head space. The peppers may rise a bit when fermenting.
Next, mix 1 quart unchlorinated water with 3 tablespoons sea salt. Pour just enough brine over the peppers to cover them, pressing them down a bit as you go. It is important to keep the peppers covered with brine to avoid spoilage. Check this daily.
Screw on the lid and set the jar away from direct sunlight to ferment for at least 1 week. Ideal temperatures are between 55-75 degrees F. The most active fermentation period is between 1-2 weeks, so be sure to monitor it during this time. “Burp” the jars often by unscrewing the lid a bit to let out some of the accumulating gases. Or, use an airlock or membrane for easier fermenting. See our page, “How to Ferment Peppers”, for more detailed instruction.
After 1-2 weeks, the fermenting activity will diminish and the brine will turn cloudy and taste acidic.
Drain the peppers, but reserve the brine.
Add the fermented peppers to a food processor or blender, along with 1/2 cup of the brine and 1/2 cup vinegar. You can add more or less of each as desired to your preference. More brine will have more salty flavor, more vinegar will be more acidic.
Process until smooth.
Optional Step. Add the fermented hot sauce to a pot and bring to a quick boil. Reduce heat and simmer for 15 minutes. This will stop the fermentation process and meld the flavors, but will remove the probiotic benefits.
Strain the mixture to remove the solids if desired, or use as-is for a thicker hot sauce. Pour into hot sauce bottles and enjoy.
You can add more vinegar or water to thin out the hot sauce.