The four enemies
Dried spirulina is shelf-stable but not indefinitely. Four things actively degrade it, in roughly this order of severity:
- Light — UV and visible light bleach phycocyanin within weeks. The bright blue-green pigment is light-sensitive almost by definition.
- Heat — sustained warmth accelerates oxidation of phycocyanin and B-vitamins. A spice rack above the stove is a bad idea.
- Oxygen — once a container is opened, air contact drives slow oxidation. Half-empty jars age faster than full ones.
- Moisture — humidity above ~10% relative water content invites mould and rapid microbial growth.
The simple rule
Practical answers to common questions
Should I refrigerate or freeze it?
Freezing is excellent for long-term storage of bulk spirulina — phycocyanin loss approaches zero at –18 °C. Refrigeration is helpful in hot or humid climates but introduces condensation risk every time you open the container. If you buy in bulk, freeze most of it in small portion bags and keep one working jar at room temperature.
What about the bag a producer ships it in?
Modern foil-lined re-sealable pouches are excellent — they block light and reduce oxygen exposure. The trick is squeezing the air out before re-sealing. For a re-sealable jar, pressing a square of cling film directly onto the powder surface before screwing the lid back on dramatically slows oxidation.
How long after opening?
About six months at room temperature in a properly sealed container, before the colour and flavour audibly drop. Frozen, at least 18 months. Tablets last longer than powder because their compression reduces surface-area exposure to air.
Does fridge condensation matter?
Yes. Every time you take a cold jar out of the fridge into a warm room, water condenses on the inside walls and onto the powder. Over weeks this introduces measurable moisture. If you refrigerate, take the jar out, leave it sealed for 30 minutes to warm before opening — or pre-portion into smaller jars and only open one at a time.
How to tell when it’s past it
The signs, in order of subtlety:
- The smell. Fresh spirulina smells lake-y and slightly grassy. Old spirulina smells fishy or stale-cardboard.
- The colour. Vivid teal-green is fresh. A muted, brownish-green is older and lower in phycocyanin.
- The taste in water. A teaspoon stirred into cold water should taste mildly oceanic; fresh spirulina has a clean finish. Older spirulina turns bitter on the back of the tongue.
- The colour of your smoothie. Fresh spirulina turns a banana smoothie a deep teal; aged spirulina pulls it muddy.
Any obvious off-smell, mould, or clumping is a hard stop. Throw it away.
If you home-grow fresh spirulina
Fresh paste or wet biomass is a different storage problem entirely. Refrigerate airtight; use within 3–4 days; freeze in ice-cube trays for longer-term portions. Never leave fresh spirulina at room temperature for more than a few hours — its high water content makes it as perishable as any leafy vegetable.
Next: quality & purity — what to look for before the spirulina enters your storage situation.