Erythritol is polyol (natural sugar alcohol) which is used in baking as a substitute sweetener for low carb diets. It is low in calories. It is 70% as sweet as table sugar. Erythritol does not affect blood sugar or tooth decay. Erythritol is found in a variety of foods and fermented foods. It is made by breaking down the food starch into glucose. Yeast is then added called moniliella pollinnis, by fermentation, it is then broken down to glucose.
You will most likely find this in health food stores. Finding it in a local grocery store may be more difficult.