8 How to Harvest
Your culture looks thick and dark? That's great! Now we can start harvesting. Most microorganisms (harmful bacteria) cannot thrive in an alkaline environment (> pH 10.5) except for Spirulina, so if you treat it right it is definitely safe to consume!​​​​​​​
→ Duration: approx. 20-30 minutes
• If you wish to harvest daily, you should harvest only 1/4 of the total volume. If you prefer to harvest more, that's fine but you shouldn't harvest more than 1/2 of the volume every few days.
• I recommend consuming in the morning. It turns out that Spirulina biomass has higher protein content at sunrise than sunset; sunrise culture has around 10% more protein. So you can either harvest in the morning and consume it right away or harvest in the night and keep it in the fridge overnight.
• Make sure that the harvesting funnel and container are below the primary cultivation vessel. (see 1.5)
• Before the harvest, wash everything with water (harvesting funnel+parts, filter cloth, tube, and air control valve).
⚠︎ DO NOT USE HOT WATER WITH 3D PRINTED PARTS AS PLA WARPS AT 60-65 °C (140-150 °F) ⚠︎
8.1 Measure Culture Concentration / pH
• Use the litmus paper to make sure the pH is 10-11.
• Use the Secchi ruler to measure the concentration. Dip the ruler into the water, lower it until the rounded white surface disappears, stop at that position and read the number; if it's below 3cm, you can harvest.
• Never eat your Spirulina if the pH is below 10 or above 11!
If pH is below 10 but looks thick give it a couple of days and it should rise—then you can harvest. If pH remains steady, you may need more nutrients. If your pH has risen to 11 or above it is time to change your medium.
[source: How to Grow Spirulina at Home]​​​​​​​
8.2 Set Up the Harvesting Funnel
• Put the ring between the cylinder and the funnel. Tighten by twisting the cylinder along the threaded body.
• Cut the filter cloth into a square (30x30cm) and put it on top of the funnel. Use the clips to lock it in place, be sure it stretches tightly across.
• Use a ruler (or anything flat) to push the cloth inside the edges.
• Insert air control valve in between a short tube (4-6cm) and a long tube (length depends on the distance between your cultivation container and harvesting container).
8.3 Syphon and Filter 1/4 of The Culture
→ If you use a beverage dispenser (see above) as a cultivation container please skip to 8.4
• Put the long tube into the vessel, make sure the lever is in a position that allows flow. 
• Turn off the air pump.
• On the short end, Suck the liquid up really gently, as the culture slowly travels up through the tube and the valve, you can then stop the flow by turning the lever 90°.
• Be careful not to suck it as you would do with a straw. Though the culture medium is harmless; it’s salty, so it’s not fun to drink.
• Put the tube in a locking position in one of the clips then turn the valve back on.
8.4 Use a Spatula to Circulate the Accumulated Culture
• As Spirulina accumulates on the surface of the filter cloth, the medium begins to go through the filter cloth more slowly, you'll have to turn the valve off/on intermittently to prevent overflow.
• Use a spatula to circulate the culture to speed up the flow.
• Hold the tube above the cultivation vessel and turn the valve on to empty the tube and release the culture back into the vessel.

You can also use a baster to speed up the process

8.5 Squeeze Out Excess Liquid
• After the medium is drained, direct the Spirulina paste into the centre.
• Unclip the cloth from the funnel.
• Gently squeeze out excess liquid. (you can also not squeeze if you prefer).
8.6 Weigh the Harvested Spirulina
• Weigh the harvested Spirulina. This is important since this determines how much you'll need to put the nutrients back into the filtered medium. Once you've harvested several times you can skip weighing, if the numbers are consistent then you can stick to the approximate weight.
• Scrape the Spirulina paste off the cloth.
• Rinse filter cloth by dipping it into the filtered medium or in the glass of water and drink immediately.
8.7 Add the Nutrients
• Add the nutrients into the filtered medium (the same amount as harvested Spirulina).
• Swirl the harvesting container a couple of times.
8.8 Pour the Medium Back into The Container
• Pour the filtered medium back into the cultivation container.
In this way, the water gets recycled for a period of 4-6 months until you have to renew it.
• Close the lid.
8.9 Wash the Equipment + Harvesting 
• Rinse all the equipment and harvesting container with water, soap isn't necessary except for the very first time before you use it. If you wish to wash them with soap every time after the harvest, then by all means.
8.10 Sit Back and Relax
• Wait until Spirulina thickens to the harvestable stage again then repeat!
Message from the Creator
Once you're accustomed to your culture, you'll be able to identify the concentration without using the Secchi ruler, you could just tell by observing/looking at it. Alright, now that you've got the fresh green paste, let's eat!
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