The Complete Guide to Harvesting Spirulina

The Complete Guide to Harvesting Spirulina

Harvesting spirulina is a delicate process that requires attention, precision and above all, hygiene. Preferably, it should be done with minimum human intervention, to avoid contamination. While there are many ways to harvest and dry the fresh spirulina biomass, it is essential that you use proper harvesting equipment. In this article, we’ve gone over four pieces of harvesting gear which we found to be extremely useful in a small scale spirulina production environments, such as your home, lab or microfarm setup.

Checking Your Samples

Before doing anything, its very important to make sure that your Spirulina is indeed safe to use. We’re not going go into detail about the types of contamination that can occur when spirulina isn’t maintained correctly, but let’s just say its good to see things with your own eyes. Looking at your samples under a microscope, you should be able to see spirals and nothing else. If any other organism is present in the sample, it means that your batch has been contaminated and should be pre-filtered or re-inoculated.

AmScope M170C-E 40X-1000X Dual LED Solid-metal Portable Compound Microscope with Camera
AmScope M170C-E 40X-1000X Dual LED Solid-metal Portable Compound Microscope with Camera


Filtering Spirulina Through a Harvesting Mesh

On the first stage of harvesting spirulina, a tight nylon filter of 30 microns is used to separate the biomass of spirulina from the liquid culture. To do that, many spirulina producers choose to attach the mesh to a wooden frame above their pond and rake the liquids through the framed filter until a thick green paste is formed on the top.

The Nylon fibers of the harvesting filter ensure that no liquids are absorbed in the fabric, and the tight density enables you to collect the fresh biomass while leaving some of the culture to reproduce after the harvest is complete.

If you find that the 30-micron mesh isn’t sufficient, it may be the case that your Spirulina cells, AKA coils, have gone from curly to straight, and are passing through the filter too easily. While not ideal, you should still be able to harvest your spirulina with a tighter, 50 microns filter.

If you’re on a low budget, you can still find good quality filters for a much lower price, like the ones by Chemistry hippy.

Chemistry Hippie | 50 Micron Pressing Screens 6-pack | Essential Oil Concentrate Press Filter | Ultra Strong 5x5 Inch Sheets | Also Available in 25, 100, and 150 Micron Screens
Chemistry Hippie | 50 Micron Pressing Screens 6-pack | Essential Oil Concentrate Press Filter | Ultra Strong 5×5 Inch Sheets | Also Available in 25, 100, and 150 Micron Screens

Mesh Vs. Microns

Choosing the right filter can be confusing if you’re not familiar with the terminology. Filter size is sometimes rated in U.S. Mesh instead of microns. While U.S. Mesh represents the number of wires (or threads) per linear inch, Microns represent the size of the holes. Basically, the higher the Mesh, the lower the Microns. Use the table below to help you determine the density of your filter.

Filter densities in Mesh, Inches, Millimeters and Microns

To visualize the numbers, here’s what different filter sizes look like:

Mesh Micron filters for spirulina harvesting

Other Filtering Techniques

There are many different techniques for filtering the biomass. Many of them use vibration or air insertion to prevent the harvested biomass from blocking the filter, such as this example:

commercial spirulina harvesting machine

The fresh biomass should be washed and drained at least 2 more times before finally squeezing out all the excess water and heading over to the drying/ preserving process. This will reduce the pH to a more human friendly level as well as remove the salty taste to some extent. Most importantly, it will help to remove excess nutrients from the product.

While home growers can easily do with a bucket and filtering clots, new technologies are now being applied in larger scale operations to quickly extract the fresh spirulina biomass out of the water. Here’s one example from italian manufacturer Virto-Cuccolini:

Weighing Your Spirulina Harvest

There are two reasons why you’d want to weigh your product right after the harvest. The obvious one is of course, that you want to know how much you’ve harvested. But more importantly, the weight of your harvest will determine how much to feed your spirulina culture so that it grows back again.

The weighing of spirulina is done twice. The first time, as mentioned above, is right after the harvest, when the biomass is squeezed of water but still relatively wet. And the second time is after the drying process is complete. This way, you can find out the level of humidity inside the product and see the difference in weight.

There are many types of scales on the market. If you’re a home grower, a simple kitchen scale with 0.01 accuracy will do the trick. If you’re growing spirulina on a larger scale, or if you want to get higher accuracy, auto calibration and other measuring features, you can go for a more professional scale like this one.

weighing spirulina harvest biomass with Laboratory Scales for food industry
Bonvoisin Lab Scale 5000gx0.01g High Precision Electronic Scales

Making Sun-Dried Spirulina Crunchies

After harvesting, there are several ways to preserve the spirulina. One of them is, of course, freezing it, which is considered to be the best at preserving spirulina nutrients. However, if you need to ensure shelf life, drying the spirulina seems to be the most effective method. While commercial producers may prefer to use a spray dryer for a faster, cleaner process, home growers will find joy in sun drying, which is easier and a lot more energy efficient.

One of our favorite tools to produce sun-dried spirulina is the spaghetti maker because It’s such a simple tool that can be found just about anywhere.

Obmwang Spirulina Crunchies Noodles Machine,pasta Maker,citrus Juicer,stainless Steel
Obmwang Spirulina Crunchies Noodles Machine,Stainless Steel

Simply insert the freshly squeezed spirulina biomass into the spaghetti maker and press the noodles out onto a drying mesh. Depending on the amount of harvest you have, you might want to consider these clothes drying racks, which, surprisingly, as perfect for drying spirulina at home. A basic structure like the one below is easy to find and relatively cheap, though more advanced models are available for industrial producers.

spirulina drying rack- the complete guide to spirulina harvesting
Originally for drying laundry, this simple drying rack is perfect for drying homegrown spirulina
Dried Spirulina Crunchies
Dried Spirulina Crunchies

Despite the name of this method, it’s actually better to dry spirulina in the shade or even indoors, if the weather allows it, as direct sunlight could harm the pigments which are so valuable to our health. To speed up this process, you can use an electric food dehydrator like this one:

electric food dehydrator for drying spirulina biomass after harvesting


There are many ways to harvest and preserve spirulina. In this guide, we’ve included a few of them to give you a taste of what harvesting spirulina is all about, as well as a few of the tools that we like to use as small scale growers. Think we missed something? Got a better idea? Let us know in the comments below.

Happy Harvesting!

21 Responses

  1. philani Reply


    What are the optimal growth condition for spirulina . We just bought the fresh culture this week, we find that some are long helix shape that are coiled around and some are just straight trichomes, any reasons for that or i be worried about different shapes under microscope.


    • Ditsa Keren Reply

      Hi Philani, straight trichomes are a sign that the culture has been under stress, possibly due to excessive light. You should try to separate them from the rest of the culture as much as possible, as those will be difficult to harvest.

  2. philani Reply


    very informative article.


  3. rani9392440853 Reply

    Hi how to increase pH value in spirulina cultivation

  4. Sunil Bhargav Reply

    What is organic spirulina? Is spirulina is available in tablets?

  5. Md Masudur Rahman Reply

    Nice and informative article

  6. Mouhcine GUENFOUD Reply

    Please do you know where can I buy the Greenbubble Sprulina Harvesting machine ??

  7. Mohamed Fouad Reply

    If I’m using a spirulina raceway is typical harvesting from the upper water surface or the bottom or it doesn’t matter?

    • Ditsa Keren Reply

      That’s debatable. With proper mixing, there should be no difference, but if you do have sediments, bottom is probably better. That said, if the sediment is brown or miscolored, it should be separated from the green, healthy harvet and scooped out of the pond.

  8. Ashley wallis Reply

    Hi do you know where i can buy that filter?

  9. Ursulo Yapo Reply

    Buen día cuanto debo alimentar por 1kg de masa seca? gracias

  10. Nitin chaudhari Reply

    What is the formula of harvesting organic spirulina
    I mean fertigation part, pls tell
    And process of fertigation per 1000 litre. Please tell adding material in cultivation pond.

  11. Mark Reply


    I got confused with the filter sizes, when you said tighter 50 microns mesh. I presume that what is being reffered in microns are the hole size. If this is the case, then a 30 microns mesh would be tighter than a 50, not the other way around.

    Unless you are referring to the mesh size , which i believe holes get smaller as you increase the number.


    • Ditsa Keren Reply

      Hi Mark, thanks for your comment. I added an image to clarify this issue.

    • Paul Reply


      Mesh size is basically the number of openings in a linear inch. It means in 50 mesh you will find 50 numbers of opening in one inch, while 30 mesh will have 30 opening. Hence the 30 mesh will have larger opening size.

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