It has been about 5 years since the last time I made fermented substrate for the scarab beetle rearing. As the number of beetle larvae (in captivity) has increased recently, I decided to make some additional (of about 50 L) before the summer goes. Scarab beetle larvae feed on dead plant materials from decayed wood to soil, and in captivity, they can be fed with fermented substrate (sawdust). Such items can easily be acquired from a regular pet store in South Korea (as well as Japan, China, Taiwan, etc.) where they keep insects as common pet animals. However, that’s not the case in the U.S., and I had to make it on my own for the last decade. This is like my 10th or maybe even 20th time making it, and I made more than couple hundreds of liters of substrate. It is not a difficult task, but just a time consuming work (as it can take about a month to three months).
The main material (substrate) I’ll be using is an item that is originally manufactured for BBQ grilling. I’m using this oak wood pellet from Traeger Grills. The Traeger Grills offer various wood pellets and grills, as well as many different items for outdoor grilling and cooking.
When you add warm to hot water to the wood pellets, it dissolves and becomes very fine-particle substrate. This is not what I need as a final product, of course, and now I have to add couple of things to trigger to ferment. I had to dry the substrate at sunlight first for about 5 hours to deter any odor in it, and to easily mix other things. Wood pellets made by pressurizing a pulverized wood powders using a machine (with heat and strong pressure), and while doing that, adhesive-like substances are produced from the wood (naturally) that makes the pellets stay together in its shape (without any other chemical additives, like a glue). To this, I’m adding a pack of dry dog food (as additives) and yeast and beer (as ferment starter). In case of dog food, I ground it to powder beforehand.
I didn’t select a particular dog food. I just grabbed a cheap one from Dollar Tree, and it goes same for yeast (from Walmart).
I mixed up these three items (substrate, dog food, yeast) little by little for easier works. I used up all the dog food, that is about 400 grams and yeast for 118 grams. The amount of additives differs per what you are using. I’m only adding this much of dog food, but it would be better to add 3 to 4 times more for wheat flour. Additives ONLY help the process of fermentation. You must add ferment starter to properly trigger the fermentation. The easy combination is as follows, [substrate (100)] : [wheat flour (10-15)] : [yeast (10-ish)]. I know I didn’t follow this rule, but things can be changed per what you are adding in. The wheat flour helps raising up the heat in fermentation, but a dog food can help it a lot better, so I’m just using small amount of a dog food with small amount of yeast.
Although I’ve already added yeast, I decided to add cans of beer as well to also add some water into it. Beer is fermented product, so it can be used as ferment starter, and it works great (not that I mean you can add all kinds of fermented products like pickles or kimchi). I succeeded all the time even when I only used beer and wheat flour.
Now add some holes for the better ventilation. This fermentation is aerotropic, (with air=aerotropic; without air=anaerobic) so it requires a regular ventilation. Now, lid on, and keep in warm and dark place, with a mixture (for ventilation) every once in 7-10 days. It will start to ferment in couple of days, and it will start to smell like a sweet, pineapple punch juice (in my case), but it just smells bad if failed. If you failed, then simply dry it out completely and try again.
As it starts to ferment, temperature inside the substrate rises up even over 70˚C (158˚F) and kills all the currently existing microorganisms, and starts new cultures (good for larval developments). Depending on amount of substrate, the temperature may or may not rise above the 70˚C. My previous works from 10L to 20L ranged around 50˚C to 70˚C. I’m hoping the temperature this time goes above that previous range. Depending on how much temperature arose, the color of final product may differ. As the temperature rises up, the color gets darker in final product. So the color itself cannot tell you how nutritious it may be.
Updates on August 29th, 2018:
After couple days, hyphae start to spread out on the surface, and this means it is properly started. Hyphae is white, spiderweb-like fungus shown on the images above. Click it to view enlarged images. If you see molds in black, orange, red, and/or green colored, that means it is failed to fermenting, so just dry it out completely and do it again.
Updates on November 19th, 2018:
The fermentation has completed a while ago, but I’m just updating now (November 19th, 2018) to show the difference in color of before and after the fermentation.