Clean anhydrous weed, usually shortened to CAW, is the share of a dried seaweed lot that is actually seaweed: what remains once the water, surface salt, sand and other foreign matter are taken out. Gross weight tells a carrageenan processor how much it has paid for. CAW tells it how much raw material it has really bought. The two can differ a great deal, and that gap is where many of the arguments between seaweed sellers and factories begin.
What CAW Measures
The idea is simple even if laboratory procedures vary. A representative sample is weighed as received. It is then washed to dissolve surface salt and remove sand and debris, foreign material is picked out by hand, and the cleaned seaweed is dried until its weight no longer changes. The final dry, clean weight is expressed as a proportion of the original sample weight.
Because the test strips away everything that is not seaweed, it combines several quality defects into one figure. That makes it a convenient basis for pricing and comparison between suppliers, provided both sides use the same method. Contracts that rely on CAW should describe that method, or name the laboratory, just as they do for moisture content.
Why Processors Prefer It to Gross Weight
A carrageenan factory pays for seaweed, freight, handling and storage by the tonne, then extracts carrageenan from what is left after washing. Water and salt do not produce carrageenan; sand wears equipment and must be disposed of; rope fragments and plastic have to be removed. Two lots of equal weight can therefore deliver quite different amounts of usable material.
CAW is not the same as carrageenan yield. Two lots with the same CAW can still yield different amounts of carrageenan, or carrageenan of different gel strength, depending on species, strain, growing conditions and harvest age. Processors often look at both: CAW to understand what they have bought, and extraction tests to understand how it will perform.
What Lowers CAW
- Excess moisture: the most common cause. Seaweed that has not been dried enough, or that has absorbed humidity in storage, carries weight that disappears in the test.
- Salt: seaweed dried straight from the sea carries salt on its surface. Some salt is normal, but seaweed that is repeatedly wetted with seawater, or deliberately salted, carries far more.
- Sand, stones and mud: often picked up when seaweed is dried on bare ground or beaches rather than on raised platforms or clean mats.
- Foreign matter: tying rope, raffia, plastic, shells and other seaweed species mixed into the lot.
- Harvest age: seaweed harvested too young is widely reported to give poorer carrageenan results, even if it does not reduce CAW directly.
Nearly all of these are decided at the farm and at the first collection point. Our article on why drying decides the price looks at the drying stage in detail.
How Suppliers Can Protect the Figure
- Harvest at the right age rather than early to meet a cash need.
- Dry on raised racks, nets or clean tarpaulins, away from sand and standing water.
- Keep seaweed covered from rain and avoid rewetting it with seawater.
- Remove ties, rope ends and other species before packing.
- Store sacks off the floor in a dry, ventilated building.
- Keep lots from different groups separate, so a low result can be traced to its source.
The last point matters more than it seems. When lots are mixed, one poorly handled consignment lowers the result for everyone. Separation and records, as described in our article on traceability, let a buyer and supplier fix the problem at its source.
Frequently asked questions
Is CAW the same as dry weight?
Not quite. Dry weight removes only water. CAW also removes salt, sand and foreign matter, so it is always lower than dry weight for the same sample.
Does a high CAW guarantee good carrageenan?
No. It shows the lot is clean and dry, but carrageenan content and gel quality also depend on species, strain, growing conditions and harvest age. Extraction tests answer that question.
Who should run the CAW test?
Whoever the contract names: the buyer’s laboratory, the seller’s, or an independent inspector. What matters is that the method is agreed in advance and applied to properly drawn samples.
Working with Kospermindo
Kospermindo works with organised farmer groups in South and Central Sulawesi, providing mentoring and technical assistance through its Farmer Group Centres. See our page on cottonii cultivation or contact us.