We know substrates are crucial to grow beetles grubs. It determines whether the eggs hatch, whether the grubs survive to adults as well as the size of the adult beetles. In this guide, I’ll teach you how to make flake soils for your beetles. 

To prepare the flake soil, mix activated 0.2 lbs yeast, 0.4 lbs wheat flour, 0.4 lbs corn flour, 0.2 lbs white sugar, and 0.2 lbs brown sugar with 20 lbs hardwood sawdust. Add water into the mixture and stir evenly until the mixture is moist but not wet. Leave the mixture in a closed and ventilated container for 6 weeks and it is ready for use. Dry the flake soil to store it.

Preparing your flake soil for the first time can be scary, especially when you have limited beetles to risk. Continue reading to understand more on flake soil so that you can make your own flake soil with success. 

Why Should I Make My Own Flake Soil?

Flake soil is a highly reputable substrate that many beetle keepers use with a high success rate. It is basically fermented woods supplemented with nutrients for the grubs to feed on. While you can definitely buy flake soil from the pet stores, the major setback for serious beetle keepers is the price. Depending on where you are, it can cost you from USD 5.5/gallon to USD 20/gallon. That is very expensive, considering you need a few gallons of flake soil for a grub to reach adulthood!

The second reason is the supply availability. It is very difficult to get flake soil in certain regions, where beetle keeping is not popular. If you did find a supplier and one day he decides to shift to something more profitable, you can’t find a replacement because it is so rare in your region. 

The third reason lies in supply consistency. It is very crucial to supply the same grub with the same flake soil. If you move the grubs from flake soil brand A to flake soil brand B, it may shock and stress them, making them less healthy or even kill them. Many flake soil suppliers are making flake soil as a side income. Hence, the supply is not consistent, and they might not be able to respond to sudden surge of demands.

Having said that, if you do not plan to keep beetles for a long term, you should just buy flake soil instead of making it by yourself.


Here is the list of ingredients required to prepare flake soil

  • Yeast (0.2 lbs/100 g)
  • Wheat flour (0.4 lbs/200 g)
  • Corn flour (0.4 lbs/200 g)
  • White sugar (0.2 lbs/100 g)
  • Brown sugar (0.2 lbs/100 g)
  • Hardwood sawdust (20 lbs/10 kg) or pellet (updated)
  • Water

Activating the Yeast

It is very important to activate your yeast, if the label says “active dried yeasts”. To activate your yeast, place them into a bowl and add the same amount of sugar. Pour some warm water (100-110 °F/38-43 °C) into the bowl and stir the mixture vigorously for a few seconds. Cover the bowl and leave it for 30 minutes. You should see some broth floating on the bowl. The yeast is now activated. You do not need to activate the yeast if it is an instant yeast formulation. 

Mixing the Ingredients

Our ultimate objective is to obtain fermented wood so that we can feed our grubs. This recipe is meant for Hercules beetles, goliath beetles and lucanid beetles which feed on hardwood. Make sure you are using hardwood.

Mixing sawdust and water is actually sufficient to ferment the wood, but it is very slow. That’s why additives (such as flour and sugar) are added to expedite the process, in addition to adding extra nutrients into the soil. 

You can actually modify the composition of the additives based on your preference. For instance, you can choose to use only wheat flour but not corn flour, or adjust the amount of sugar. It is all up to you. Some people even use rice husk, honey, and/or protein powder.

The more additives you include, the higher the risk of fermentation failure, the higher the risk of your grubs dying, and the shorter the shelf life of your flake soil. As a general rule of thumb, additives should be less than 10% of the sawdust. 

You should start mixing the sawdust and additives while activating your yeast. Use a tray double the size of your mixture so that it is easier to mix your ingredients.

Mixing the ingredients. Use a big tray so that it is easier to mix the substrates

Make sure the sawdust and additives are dry when mixing them. Otherwise, they may form a big block (due to water) and it can be difficult to mix them evenly. After mixing the ingredients, add in the activated yeast, followed by water. 

Updated: Variation Using Hardwood Pellet

I recently tried making flake soil using hardwood pellet instead of sawdust. I found that using pellet is much more convenient than using sawdust.

Wooden pellets are compacted, making them small and space-saving. As a result, shipping is much cheaper than sawdust. Moreover, wood pellets are more readily available than sawdust.

Here’s an affiliate link to hardwood pellets that you can get from Amazon.

Pour the desired amount of pellets into a tray and add some warm water. You should notice the pellets started swelling. Crush those swollen pellets with your hands. Add water as you crush those pellets. Then, pour in the rest of the additives and yeast. Mix them well.

How Much Water to Add?

The ratio of sawdust and water is around 3:2 (volume to volume) but it depends on the sawdust that you use. Continue to stir the mixture while you pour the water until the mixture is evenly moist. 

But how moist is moist? Take a handful of the mixture and squeeze it. It should hold its shape momentarily without water coming out. If the mixture doesn’t hold its shape at all, add more water. If there is dripping water when you squeeze it, add more sawdust.

Sawdust with optimal moisture

If you are preparing a lot of flake soil in a big mixing container at one time, make sure you test the mixture from the 4 corners and the center of your container to ensure the mixture is evenly moist. 


Put the mixture into a container, around 80% full. Do not compress the mixture. Cover it with a lid and . Be careful not to store it in a manner where other creatures (especially insects) can get into it.

You can also store the mixture in a tote bag. But note that the mixture will dry much faster. So you will need to add water frequently.

Put the mixture at a warm (>77 °F/25 °C), dark place. Stir the mixture every 2-3 days aerate the fermenting wood at the bottom. Add water if it becomes too dry.

You should also notice some heat generated from the fermenting wood, which is normal. If there is no heat generated, very likely the fermentation did not happen. I usually keep the soil in a bigger container so that heat produced during the fermentation can be preserved better. Remember, a little bit of extra heat helps fermentation.

Some people advise putting tree branches into the fermenting wood but I would advise against it. The tree branches may contain creatures such as mites, which are harmful to your beetles.

The fermentation stops after 4-6 weeks, where the mixture no longer produce any heat. It can be shorter or longer depending on the temperature. At warmer temperature, the fermentation is faster and vice versa. I usually make my flake soil in the hot season so it takes about 3-4 weeks to complete.

Another sign of completed fermentation is the dark brown color of the flake soil. A dark colored product signifies the fermentation is sufficient, and it is ready to be used for the grubs.

During the fermentation, gases are generated. Make sure you do not make the container airtight or the container may burst. There will be some alcoholic/fruity odor coming out from the fermenting mixture, which is completely normal. The smell can be unpleasant depending on the additives that you use.

However, if it smells awful – like ammonia, feces, or vinegar, the woods are rotten. You need to redo everything. This is likely due to too many additives being added or too much water.

Storing Flake Soil

If you need to store the flake soil, you need to dry it completely. Do this by spreading the soil evenly on a piece of sheet under the sun. Once dried, keep them in an airtight container. You can keep your flake soil for a year if it is completely dried. Just make sure no bugs infiltrate your flake soil during the storage period.

Last Words

There are many flake soil recipes out there, with different additives, different wood to water ratio. Feel free to experiment with different combinations to come out with the best formulation for your grubs.

Additional Information

Common causes of failed fermentation:

  • Too much water is added. Be conservative when adding water. When pressed in hand, the mixture should hold in shape and there should not be water dripping.
  • Low surrounding temperature. It should be higher than 77 °F/25 °C
  • Too much additives are added. Additives is a double edge sword. The purpose of adding those additives (eg. flour) is to improve the nutrients composition of the flake soil and the speed of fermentation. However, adding too much of them can promote putrefaction. Try to keep them below 10% of your wood.