Gelatin is a colorless, tasteless, water-soluble substance derived from the collagen found inside animal bones and skin. Gelatin comes in powdered form and in sheets; but they both need to be soaked in cold/ cool water for 10 – 15 minutes before being dissolved under high temperature. This “blooming” process allows gelatin to soak up water or liquid before blending with other ingredients.
Although both Gelatin and Agar are thickening agent, they are different from each other in many aspects. First, Gelatin melts at a much lower degree than Agar. The melting point of Gelatin is about 35 degrees C (95 degrees F) while, that of Agar is 85 degrees C (185 degrees F). Hence, Agar needs to be brought to a boil while gelatin can be dissolved in hot liquid and left to solidify (normally in the fridge). More broadly speaking, liquid that contains Gelatin needs more time (and lower temperature) to solidify than liquid contains Agar. Food with Gelatin also melts faster.
Second, Gelatin provides a more elastic and jelly-like texture to the food, while Agar provides a crunchier texture. Therefore, in many cases, Gelatin should not be substituted by Agar and vice versa.