Harvesting and Using Fresh Spirulina

Harvesting Spirulina is refreshingly low-tech: because the organism forms filaments, it can be caught on a fine cloth or mesh while the growth medium drains through. Harvest when the culture is dense — deep green and nearly opaque — and never take all of it; leave a good fraction as living inoculum for the next batch. Harvesting perhaps a quarter to a third and topping up with fresh medium keeps it going semi-continuously.

To separate the biomass, pour the culture through mesh in the range of roughly 20–50 microns — fine enough to catch the filaments while letting the liquid pass. What collects is a thick blue-green paste. Rinse it gently with clean fresh water to wash off residual alkaline medium (you do not want to eat the high-pH salts) and let it drain.

Food safety deserves real attention. The high-pH culture is inhospitable to many pathogens while growing, but harvested wet paste at room temperature is a perfect medium for bacteria — treat it like any fresh perishable. Work with clean hands and utensils, and only harvest from a culture that looks and smells healthy. Never consume one that smells rotten or shows contamination; if in doubt, throw it out. Use fresh paste quickly — refrigerate and consume within a day or two, or dry at low temperature (heat degrades some phycocyanin) or freeze for longer storage.