After inoculation of Aspergillus oryzae and other fungi (Nuruk) to the steamed rice and filtered water (0.1:1:1). Fermentation begins at room temperature (75 F)!
Nuruk can be purchased from Korea, but I prefer to make it in-house because it is difficult to find it in the States. Nuruk production is tricky, but it is fun too. Solid-state fermentation is the process to make Nuruk. Substrate is wheat (coarse mashed) and mixed with little bit of water, and then formulate in round or rectangular block. Cover the block with a source of fungi (dried corn stalk will work instead of rice stalk), and then set them in a dark and dry place for 4-8 weeks. Keep the temperature 75-85 F. I use my attic. You need to flip flop the wheat block twice per week.
What you look for is “dark yellowish or white” fungi (Aspergillus oryzae or nidulans) on wheat block. If you see “black” fungi, those are Aspergillus niger, which produces “dark” color Makkgeolli rice wine, so sort them out and burn them away.
I spent last two whole months to make some good quality Nuruk, so if you wish, I can share some which may be enough for a small test batch.
After 48 hours of fermentation, inside temperature elevates to 78 F from 75F, and pH reaches to 4.0 from 8.0. Fully swollen rice is obvious, and some rices start floating.
After 90 hours of fermentation, residual rices decreased to almost half of the initial mass, and no more ethanol bubble produced. Time to stop and start downstream process.
After series of filtration with decreasing mesh number of sieves, final product with 1:2 dilution with water reveals wonderful color of milky white. Estimated alcohol concentration is 5-6% (v/v). Now MatKorea is ready for fun. Taste before dilution is very bold and strong, as well as sour, so you may want to add your favorite flavor(s), for instance, sugar, maple syrup, fruit extracts, whatever you like.... And also you can control alcohol concentration. Since the original liquid has almost 15% alcohol in it, you can dilute accordingly to get your own alcohol level and your own flavor...
Do you prefer Sake? Then distill the final product, then you get yourself Sake!!
But since MatKorea contains LOTS of lactic acid bacteria, which is the results of carbohydrate fermentation, your skin cells will become lovely if you have skin trouble. Due to the same action of lactic acid bacteria, it contains LOTs of other nutrients which are easy to digest without burden to your stomach. So, MatKorea has been popular to Korean people for last 2000 years…..
Well, this is it for my first post and I’m a Chem E. engineer who professionally ferments bacteria, yeast, fungi for vaccine, antibodies, metabolites production, well, whatever keeps my job…
Hope this helps…. And most importantly, have fun!
