Why Are Eggshells Microwaved Before Composting?

  • By: composthq
  • Date: October 16, 2021
  • Time to read: 5 min.

Why Are Eggshells Microwaved Before Composting?

Long story short: they need to be as dry as possible before composting. While microwaving your eggshells might seem like a particularly strange step to take before composting, but trust us, it works.

There are a whole host of reasons that you should be adding eggs into your compost (alongside an even bigger host of myths about the benefits of these shells).

If you were to try and use these little casings, microwaving them first is a pretty important step depending on your use case. 

Normally when applying products and supplements to your compost like eggshells, you want to be grinding and blending them into an extremely fine powder before using them.

Larger shards of egg do not really have particularly useful qualities for composting, as they do not mix well with the soil in this form. 

Microwaving your eggshells before using them in compost or mulch is an essential step as it removes any latent moisture still present in the eggshells.

These shells might not seem like a hugely wet substance, but if you want to effectively grind these shells into a fine enough powder for composting, it is an essential step. 

So, if you want to know the answer to the question “why are eggshells microwaved before composting?” Further to that, this article will answer a lot of different questions around the use of microwaved eggs in composting.

This will include looking at some general benefits and also fact-checking some common eggshell compost myths (and show why microwaving the eggs is a good step to take).

Without further ado, here is why eggshells get microwaved before composting!

What Exactly Does Microwaving Eggs Do to Them?

First things first – eggshells are not wet per se, but any moisture in them will get released when you attempt to grind them down.

These eggs first manifest as egg sacs in the chicken before being hardened, so there are trace elements of moisture that threaten to turn the shells into a dry paste rather than a fine, dry powder. 

When the microwave was discovered by Percy Spencer in the 1940s, a machine called the Magnetron was being tested in Raytheon’s labs.

Spencer noticed that when testing this machine, a chocolate bar in his pocket had melted, seemingly of its own accord.

What happened to the chocolate bar is that the water molecules in it were excited by the microwaves, moving with great speed and increasing the thermal energy in the bar, melting it. Its use on eggshells here has a similar context.

Often, if you had excess eggshells, you used to have to leave them in a hot place outside (or in an oven) in order to dry them out before grinding them into a dry powder suitable for composting.

However, Spencer’s discovery has had a massive, if definitely unintentional, impact on the process of adding eggshells into your compost.

What might have taken the better part of several days in the past can now be accomplished in a matter of minutes with the help of abundant microwave radiation.

As you microwave your eggshells, the same effect as was bestowed on Spencer’s unfortunate chocolate bar takes place. Any latent moisture that was in the eggshells gets excited, and hopefully, is turned into steam.

The water is then released from the eggshells, meaning that any moisture that would cause problems for grinding the shells is completely removed. Make sure you leave your eggshells to cool before grinding them.

Properly microwaved eggshells should be even more brittle than they usually would be, perfect for grinding.

So, I Microwaved My Eggshells: What’s Next?

You now know exactly why we microwave eggshells for composting. But how do they go from hot egg containers to a delightfully nutritious compost supplement? Well, first we grind. 

Take your cooled, microwaved and hopefully moisture-free eggshells, and put them in some kind of grinding mechanism. This could be a dedicated spice grinder, a mortar and pestle or something of that kind.

If you do not have this kind of kitchen paraphernalia, then a blender (not a hand blender) or old electric coffee grinder might work well. A lot of people repurpose old coffee grinders for grinding spices, and this might be a great tool to use here.

Make sure you thoroughly clean your spice grinder after it is used for this purpose – although a bit of eggshell powder probably will not hurt you too much.

After that, you can mix your powder in with mulch or other compost you are going to give to your plant. You can even sprinkle this powder directly onto the compost areas if you so desire.

One of the benefits of microwaving and grinding the shells into a fine powder is it means the eggs are less visible and less of an eyesore.

What Benefits Do Eggshells Have in Compost?

The chief benefit of adding eggshells into your compost is the introduction of the shell’s calcium content into your soil.

While a lot of soil is not exactly calcium deficient, it is also not calcium rich. Microwaving your eggshells and then grinding them can make a powder that spreads better, spreading the calcium rich elements of the shells into the soil. 

This calcium enhanced soil prevents a number of common ailments for plants like tomatoes. Issues like this include Blossom End Rot, which is more commonly caused by irregular watering, but giving your plants more calcium always helps. 

What Do Eggshells NOT Do? Common Eggshell Compost Myths Debunked

The above benefits come from microwaved eggshells dried and ground into a fine powder applied smartly to your compost.

There are numerous ways that eggshells get used without being microwaved that are not beneficial, however. Some claim that broken eggshells can stop slugs from accessing your plants and eating the leaves.

Unfortunately, this does not seem to be the case. As this cute little video shows, slugs can easily clamber over generously applied eggshells and would have no problem getting at your plants if the shells were used in this way. 

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