Is it possible to heat up agar gels?

As you will already know, agar-agar is a natural product extracted from red seaweed. In the food industry, it is used as a gelling, emulsifying and thickening agent and consumers can also buy it in the form of powder, flakes or transparent sheets. 

This versatile ingredient has a wide range of uses in the kitchen and can be used to modify the texture of a recipe without changing its smell, taste or colour. 

One of the most important properties of agar is the fact that it has the highest hysteresis of all hydrocolloids. As we have talked about previously, hysteresis is the difference between a gel's gelling and melting temperatures. 

To dissolve agar, it needs to be brought to boiling temperature. Then, once it has dissolved, it will turn into a gel once the temperature has fallen below 40 degrees. Agar gel is thermoreversible and, combined with its high hysteresis, this means that it can be heated up and still maintain a solid consistency, only melting again if it reaches 85-90 °C but not before. 

Therefore, and unlike gelatine, agar gels can be used in hot dishes. As a result of this property, agar began to be used in haute cuisine, thanks initially to Spanish chef Ferrán Adrià. The menu at the El Bulli restaurant first took advantage of the properties of agar with the inclusion of his legendary dish “Roquefort sorbet with hot apple jelly” at the end of the 90s.