Agar, or Agar-Agar
Of all the molecular gastronomy ingredients, agar has the most versatility. Its uses transcend this genre of cooking. Agar has been traditionally used in traditional Chinese, Japanese and Korean recipes, most often for sweet dishes. Gelatin certainly has long been used for the making of fruit jellies, aspics, pies, etc. so this really is not a modern revolutionary product. Agar is a seaweed product, which makes it a great de facto replacement for meat based gelatin, ideal for vegetarians. Normal usage involves adding agar to a cool liquid, then bringing to a boil. The gel will set when the liquid cools to around 95%F, the wonderful thing is that it stays set until the reheated liquid reaches 185F. So you can have a lot of fun serving a gelatin that is still slightly steaming. You do not use a lot of agar; 0.5 percent by weight of agar for a pretty firm gel (that is one half of one percent). Agar has the ability to replace eggs in custard dishes, puddings or sauces. It does not serve to replace the flavor of eggs, but the molecular binding produces a product of the same consistency. This is important for vegan bakery products.