Pour the vinegar in a small saucepan and warm it over medium-high heat. When the vinegar reaches 150 degrees on an instant-read thermometer, about 5 minutes. Add the lemon slices and continue to cook until the lemons are slightly translucent, about 10 minutes more.
Whisk in the black pepper, cayenne, red pepper and sugar. Continue to cook over medium-high heat until the sugar is completely dissolved and the sauce reaches 190 degrees, about 10 minutes. Remove from the heat and allow to completely cool before using. The sauce keeps in the refrigerator for one month. |