Once the harvested biomass is brought to shore, a process has to be applied quickly due to the high water content of most species.This step is not always carried out by the farmers and the level of sophistication varies between seaweed species and its designated application.The processing conversion factor is an important measure to take into account when evaluating crop and the processing yield.
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The water content of Pyropia biomass is extremely high. Consequently, processing needs to take place as soon as possible to avoid spoilage, which usually occurs after 24 hours.
In South Korea, primary processing is in many cases not done by the farmer, but carried out by dedicated processing companies that buy the fresh biomass from the farmers at the port auction. A typical processing facility has a capacity of 24,000 sheets per hour.
In Japan, primary processing is handled by the farmers themselves. According to the Japanese fishery statistics, the production volume (fresh weight) of Nori is calculated from the number of dried sheets, but the conversion rate varies in each prefecture. Usually each farmer has a small facility to produce dried Pyropia sheets, with a typical capacity of 8,000 sheets per hour.
In China, the farming company also handles primary processing into standard dry sheets. The typical capacity of such processing facilities is 7,200 sheets per hour.
Dry sheet production
The freshly harvested Pyropia biomass will go through several washing processes before it is cut, softened and turned into flakes, then dehydrated, dried, graded and finally packaged.
During the production process approximately 24~30 grams biomass will be turned into a 2.4~3.0 gram sheet, thus we speak of a conversion ratio of 10% from fresh biomass to dried sheet output. The main quality parameters are the color, taste and that the sheet has no holes.
In Korea, the production unit of dried seaweed is sold in 100 sheets (called as 1 Sok). According to Korean National technical standards (KS), the weight of 100 sheets of dried laver is 240-300g depending on the species of laver, and the weight of one sheet is 2.4-3.0g. The moisture content of dried laver is less than 14%, and in the case of twice-roasted laver, it is less than 7% (CODEX standard by CODEX Alimentarius 2017).
CODEX standard is an international food standard for Pyropia proposed by Korea, and this standard has been adopted as an international standard.