How to make Nuruk

Maji Makgeolli: How to Make Nuruk and Fermentation

What is Nuruk?

Nuruk is a traditional Korean fermentation starter primarily used in brewing alcohol.

It is made by fermenting grains like wheat or barley, and the mold and yeast produced during the fermentation process facilitate both the saccharification of starch and the production of alcohol.

Starch is broken down into sugars (maltose and glucose) by enzymes (amylase) contained in koji mold and Rhizopus (black bread mold).
Sugars are metabolized by yeasts such as Saccharomyces and Pichia to produce alcohol and carbon dioxide.
1 and 2 occur simultaneously, a process known as parallel double fermentation.

While it is similar to Japanese "koji," Nuruk has its own unique production methods and characteristics, and it is indispensable for making Korean alcoholic beverages like "Makgeolli" and "Soju."

Side Note

In a study comparing Nuruk to rice koji, it was found that although Nuruk has weaker α-amylase and glucosidase activity than rice koji, its β-amylase activity was nearly four times higher. Both are enzymes that break down starch, but because their roles and optimal temperatures differ, this can be considered one of the interesting differences between Nuruk and rice koji.

Preparing Ingredients and Tools

By preparing the necessary ingredients and tools for making Nuruk in advance, you can ensure a smooth fermentation process.

Ingredients

Wheat 1kg: While you can also make it with barley or rice, wheat has the strongest saccharification power.
Water 300ml: Be sure to use clean water.

Tools

Circular or square mold

This is a frame for pressing and compacting the ingredients. It seems that special wooden frames are sold in Korea, but they are likely unavailable in Japan. I used a round cake mold and got scolded by my wife.
Cloth
Large bowl

Making Nuruk

I have summarized the steps for actually making Nuruk.

Grind the wheat coarsely.
Mix while adding water little by little.
After mixing for 10-15 minutes, if it feels sticky, take a small piece. If it forms threads when pulled apart from the center, it's ready.
Place the mold on a table and lay the cloth over it. Spread the mixed wheat into it. Pack it firmly into the corners and edges to ensure it is even.
Twist the excess cloth tightly and tie it. Press down firmly in the center to create a depression. This provides a space for moisture to escape.
Finally, stomp on it with your feet about 20 times to compact it. If it isn't packed firmly, it will crumble easily.

The trick is to adjust the water content to achieve the appropriate consistency.

I also had the experience of it being crumbly and failing to set at first, so I just ended up eating it as porridge...

Nuruk House

Simply pressing wheat doesn't mean you've made Nuruk. You need to create a fermentation container called a "Nuruk House."

The goal is to maintain the internal temperature and humidity at the appropriate levels for the appropriate amount of time.

How to make it:

・Prepare a styrofoam box large enough to fit the Nuruk. I recommend this because it doesn't retain moisture or odors and is easy to clean.

・Punch many holes in the bottom of the styrofoam box to improve ventilation.

・Lay down straw or leaves to maintain the temperature. Materials like hemp, pine needles, or mugwort are said to be good as they have fewer pests.

It's complete. It sounds simple, but obtaining the plants can be difficult. I got some straw from a farmer.

When they asked me what I was using it for, I couldn't bring myself to say "Nuruk!"

Fermentation Tip: The 777 Method

Once you have prepared the Nuruk House, you can finally begin fermentation.

There is a method called the 777 Method to ferment it successfully.

You divide the management into three sets of one week each.

Week 1: The goal of the first seven days is to maintain humidity. Flip the Nuruk once a day and wipe away any moisture on the side walls. If the Nuruk feels warm on the 2nd or 3rd day, it is evidence that fermentation is progressing.

Week 2: Here, you gradually remove moisture. Make a hole about the size of a 10-yen coin in the lid to increase ventilation. Flip it just like in the first week. At this stage, mold on the surface will begin to penetrate the interior.

Week 3: Finally, dry it completely. Remove it from the box and let it dry in a sunny place. It’s even better if you can hang it up.

Nuruk ferments at a temperature of 30–40°C. Therefore, if the room temperature is 18–25°C, you need to place a blanket over the Nuruk House to keep it warm. Once it has dried completely, try breaking it open to look inside.

Healthy Nuruk is dry on the inside, may have small yellowish/golden or green spots here and there, and smells close to "bread."

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Thank you for reading this far.

To those of you who have grown tired of ordinary fermentation:
Why not try making Nuruk?