Liquids can also be thickened by seaweeds or gums. alginates, the main seaweed-based thickener, are used as gelling agents in the presence of calcium, but will act as thickeners in its absence. Gums are either extracted from plants (e.g. guar and locust bean (see carob) gum), or produced by certain fermentation bacteria (e.g. xanthan gum). These agents are relatively easy to use, not generally needing heat to thicken, making them ideal at thickening cold sauces, made of raw ingredients. They are generally tasteless, and thicken at low concentrations. However, thorough mixing of these sauces is needed to ensure thickening and prevent lump formation.