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3D Printing Microgreen Sprouting Jars with STL Files

Microgreens are an awesome addition to your food and growing them traditionally in a tray with soil and nutrients can sometimes be time and space consuming. There is one literally easiest way to grow micgrogreens and I think there is nothing that comes even close to this technique: A sprouting jar! If you want to know what is a sprouting jar, why it is worth to 3D print it, how it is designed and if all of this is food safe, you have come to the right blog.

Fig. 1: Red Radish in a sprouting jar without lid.


What is a sprouting jar?


In my opinion a sprouting jar is the most simple form of growing microgreens that yields awesome

results and can be done by everyone. Yes, literally everyone. Essentially you need four things:

  • A jar

  • seeds to sprout

  • water

  • some kind of mesh as a lid that lets the water out but keeps the seeds inside

While the first two are maybe the most obvious ones as they make up the name sprouting jar, the third and fourth point are also not that hard to obtain. But how do we combine them to sprout microgreens in them? Essentially in three easy steps:


  • First of all you take your jar and the seeds you want to sprout. I went with red radish, as it is not only the easiest microgreen to grow, it also has a beautiful color and, much more important, a wonderful taste that you can combine with almost every dish. For a more or less honey sized jar I took about 2-3 teaspoons of microgreen seeds and placed them in the jar.

  • Second you will now want to close the jar with your semi-open lid. Make sure the seeds really stay inside and that your mesh size is not too big.

  • And last but not least as a third point you will now rinse the seeds with water. Fill the glass all the way up and then drain it again. On the first day I do this several times and also let the water stay in the glass two or three minutes. On the following days it is just a daily rinse. After doing so place the glass upside down, so the water can drop out on the bottom until the next day. Red radish is usually ready after 4-6 days and can be eaten including the roots. Before serving it I put it in a bowl with water to strain the seed coats.


And that is it. Pretty simple, right?


Why should I 3D print a sprouting jar?


That is a very good question and I am glad you asked. Probably the best reason for me was: Because I wanted to. Spoiler: Actually I was looking for an excuse to buy and print Polypropylene, but more on this later.


There are also some technical reasons why 3D printing a sprouting jar is definitely worth it. I have a lot of jars in my kitchen with different sizes. Some are for marmelade, some for yoghurts, others had pickles in them. The only thing they have in common is the type of thread on the top. And the 3D printer allows me to make different lids that fit all the different jar sizes pretty easily. Hence I can upcycle and reuse all of my jars and grow tasty microgreen sprouts in them. Another thing, that convinced me to design and 3D print a sprouting jar was better water draining. When the jar is placed upside down it is best if you have some spacers so the water can drain more easily. I incorporated this into the design of the sprouting lid as well as some drainage holes on the ring. Most traditional sprouting jars that use meshes from e.g. stainless steel do not have those spacers and are more difficult to handle. Furthermore the stainless steel meshes come in one size. With a simple trick in the slicer when you prepare the 3D print you can adjust the mesh size to fit the size


Fig. 2: Sprouting jar with 3D printed lid standing upside down on its spacers for easier water

draining.


The design


First of all I checked the lid that was currently on the jar and I tried to mimic it in the CAD

program, so my sprouting jar lid would fit it properly. The first design I made on a honey sized jar with ~77/78mm diameter. While this was rather easy and done quickly a rather major problem came up quite fast. How to incorporate the spacers into the design?


While 3D printing sometimes feels like the holy grail of manufacturing, there is one thing it cannot to and that is a rather obvious, but most times overlooked thing: It cannot print into the air. That means if you would try to print something, that looks like the letter „T“ you would have to flip it upside down when printing, as otherwise the horizontal part would have nothing below it. Of course you could use support structures, that you remove afterward, I just like to design parts in a way that there is no support necessary.


So without the spacers, the most natural way to print a lid for a jar would be to flip it upside down, so the mesh itself is in the bottom when printing. Unfortunately that was not possible, as the spacers were needed. And while it seems most obvious, it took some time and design changes, until I figured it out the way it currently is, with the mesh rather inside of the jar on the bottom of the thread than on the outside. With this design it is possible to 3D print the lid in the upright position.


To make the mesh adjustable instead of one fixed size I used a trick in the slicer. When 3D printing the model are usually not solid but have a so called infill pattern. While there are several different patterns the one I needed was the „grid“ pattern. It looks just like the mesh that I need, but I had to program the printer to only print the infill pattern. Fortunately this is done quite easily by just removing all the top and bottom layers in the settings. Then with the infill percentage the mesh size can be adjusted. For red radish 30% infill fits perfectly, with sunflowers I recommend 20%.


Furthermore, for even easier water draining I added holes on the edges of the ring. These holes allow the water to escape even better. Since not all printers are capable of printing those I also made a design without them.



Fig. 3: 3D printed sprouting jar lids with spacers, different mesh sizes (20%, 30%, 40% infill), with and without additional drain holed on the ring.


But is all of that food safe?


That is another good and also difficult question. I could not find any manual on how to make 3D printing guaranteed food safe, but there are some precautions you can take to make it as good as possible. For my project I ordered Polypropylene, also known as PP, instead of the common materials PLA or PETG. On one hand the PP I used has a EU food grade certificate, on the other hand PP is in contrast to the other materials dish washer safe. Hence after using the lid you can easily clean it in the dishwasher. And that is an important point. Similar to plastic cutting boards, also on 3D prints, even if the material itself is food safe, it is possible that bacteria starts to grow. The easiest and most realiable way to get rid of bacteria is cleaning it at high temperatures. Best is 80°C or more (some also go with 60°C, but the higher the better) and this is easily done in a dishwasher. Also a dishwasher usually dries the dishes inside after cleaning. That further prevents bacteria growth as in a dry environment they have a hard time growing.


Regarding the printer it is probably best to exchange the standard brass nozzle for a stainless steel one, as brass may contain traces of lead. If you also print other materials than food safe PP on your printer, purging the nozzle thoroughly before printing the sprouting jar lids is mandatory to remove all residual material from previous prints.


Conclusion


Here are my takeaways for 3D printed sprouting jar lids


  • Microgreens taste awesome and with a sprouting jar they are probably the easiest thing to grow at home

  • A 3D printer can give a new life to old objects, like jars

  • While researching food safety in 3D printing I noticed, that it is not an easy task. I am not sure if there is a way to be 100% food safe, but I tried my best to get as close as possible.

I enjoyed my first harvest with the red radish and currently I have savoy cabbage growing.


The STL files to print the Sprouting Jar Lid yourself can be found on Etsy.


To see the Sprouting Jar Lid in action I recommend this video for you.


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