Cut the vanilla beans in 1” pieces and let soak in the alcohol for at least one month.
Place the vanilla beans, alcohol, rum, and water in a 1.5 quart sauce pan and bring to a simmer on low heat. Let simmer for 20-22 minutes, stirring occasionally. Use a spatula to scrape the sides of the saucepan as the mixture reduces.
Stir in the granulated sweetener until dissolved. Remove from heat and measure in the syrup. Set aside to cool.
When the mixture is cooled, pour it into a high-powered blender. Process for 5-6 minutes, stopping occasionally to scrape down the sides of the blender. If the mixture is too thick, add an additional tablespoon of rum.
When the paste is smooth, run the blender on low and slowly sprinkle in the gelatin.
Store the paste in a glass jar at room temperature. As an additional precaution to avoid mold, you may want to float an additional ½ teaspoon of rum on top of the paste.
Use beans that have been soaking in alcohol for at least a month so that they are well hydrated and more likely to process smoothly since this recipe uses the whole bean.
Because erythritol and erythritol blends tend to crystallize when cool, I used Bochasweet for the granulated sweetener. Xylitol (toxic to pets) or Allulose should work equally as well. Because of the small ratio of sweetener to the other ingredients and other factors to avoid crystallization, erythritol might also work well.
Other factors used to reduce crystallization and improve viscosity include:
Using 2 tablespoons of a commercial Allulose syrup
Adding 1 teaspoon of lemon juice
Adding sweetener after the mixture has simmered and thickened, but avoiding simmering the granulated sweetener for long periods.
Adding a thickener (gelatin) after the paste has been thoroughly processed in the blender. Other thickeners such as xanthan gum, agar agar, or konjac (glucommanan) should also work. Add very small amounts (⅛ teaspoon at a time) while blending.
Simmering the beans for 20-25 minutes brings out the natural thickeners in the vanilla beans which helps the texture in the final product.
I used this brand Allulose syrup. Another syrup should work, but some sweeteners are not generally safe for blood glucose such as maltitol, oligosaccharides, polydextrose, agave, yacon, or sorbitol.
To scale this recipe for a larger yield, start with any double fold ratio of beans to 100 proof alcohol.