I love Xantham gum for lube, but it doesn't last that long. I was reading through the xantham gum thread and found a lot of people had the same problem. So I started experimenting.
Adding a few drops of alcohol isn't going to work because to use alcohol as a preservative it needs to be 20% of the solution. I also don't think grapefruit seed extract works at all, plus it irritates the skin in high doses. I saw some people adding paraben, but after reading some safety and health concerns, I'm not sure it's something I want on my dick.
to make xantham gum lube last longer naturally.
Boil about 4 ounces of water, add 2 to 3 teaspoons of salt stir until dissolve, then let cool, mix in xantham gum as you normally would (remember not to add than xantham until it's cool). Mine last 3 weeks with salt versus 3 or 4 days without. Anything more than 3 teaspoons of salt will leave you with sandy gritty lube.
It works because the high salt content retards the growth of microbes.
I also add a little almond extract (you can find it in the baking, or spice section of most grocery stores) to make it smell like cherries. Enjoy!