The seaweed transformation procedures for the agar production vary according to the treated seaweed variety. They generally follow the 2 stages:

• The extraction

• The dehydration

The extraction is made by hot water under pressure or in open tank after washing with tap water or after alkaline treatment.

The latter is mainly applied to Gracilaria seaweed in order to lower the sulphate content in the resultant agar-agar.

The extracted juice composed of 98% water and 2% agar-agar is filtered at hot temperature, then cooled at room temperature. The resulting gel is dehydrated under mechanical pressure or by freezing-thawing.

The mechanical pressure consists in compacting gel by applying a strength of  5 to 10 kg/cm2 in a way to remove bulk water from the gel. The intercalated filters allow passing water and retain the agar-agar molecules as a cake.

The gel freezing is carried out at a temperature of 18°C that excludes selectively the agar-agar molecules from the ice net-work and form strips.The thawing step melts the ice and agar strips are recovered selectively.

These two operations of dehydration taken individually remove 70% of the initial water.

A part of the residual moisture is then eliminated by drying with hot air. The dry agar flakes are grinded to prepare a final product in powder form with different mesh sizes.