Amazake: Japan's Ancient Sweet Koji Drink Made Simple

Amazake (甘酒) is a thick, naturally sweet Japanese beverage made by fermenting cooked rice with Aspergillus oryzae — the same magical mold, known as koji, that gives us miso, sake, and soy sauce. Unlike many fermented foods that lean savory or sour, amazake surprises first-timers with its gentle, honeyed sweetness that requires zero added sugar. It has been cherished in Japan for over a thousand years as a nourishing tonic, a warming winter drink, and a cooking ingredient — and for good reason.

What Is Amazake and Why Is It So Sweet?

The sweetness in amazake is the direct result of koji's enzymatic superpower. When Aspergillus oryzae colonizes rice or other grains during the koji-making process, it produces a rich arsenal of enzymes — most importantly amylases. These enzymes break down complex starches in cooked rice into simple sugars, primarily glucose and maltose.

When you mix fresh rice koji (kome koji) with warm cooked rice and hold it at the right temperature, those amylases get to work immediately. Over 8 to 12 hours, they convert the starchy porridge into a naturally sweet, creamy drink with a flavor profile reminiscent of rice pudding and sweet mochi.

There are actually two types of amazake:

• Koji amazake (甘酒) — Made with rice koji and cooked rice, naturally alcohol-free, and the focus of this article.
• Sake lees amazake (酒粕甘酒) — Made by dissolving sake kasu (sake lees) in hot water with sugar; contains trace amounts of alcohol and has a more complex, slightly boozy flavor.

For home fermenters and beginners, koji amazake is the recommended starting point. It is alcohol-free, child-friendly, and showcases koji's enzymatic brilliance in the purest way possible.

Health Benefits of Amazake

Amazake has earned its nickname "drinkable IV drip" (飲む点滴) in Japan, and the science largely backs up the hype:

• Natural glucose for quick, sustained energy without refined sugar spikes
• Amino acids and B vitamins produced during koji fermentation, including B1, B2, and B6
• Resistant starch and dietary fiber that support gut health
• Ferulic acid and other antioxidants derived from rice bran
• Digestive enzymes that may aid in breaking down food when consumed with meals

It is also naturally gluten-free when made with rice koji, making it accessible for many dietary needs.

Ingredients You'll Need

Making koji amazake at home requires just two core ingredients and a few pieces of equipment you likely already own.

Ingredients:

• 200g rice koji (fresh or dried; fresh gives a more vibrant flavor)
• 200g Japanese short-grain rice (such as Koshihikari) or glutinous rice
• 400ml water (plus more for cooking the rice)

Optional add-ins for serving:

• Fresh grated ginger
• A pinch of sea salt (brings out sweetness)
• Matcha powder
• Citrus zest

Equipment:

• Rice cooker or heavy pot
• Instant-read thermometer (critical — do not skip this)
• Insulated container, slow cooker, or yogurt maker for fermentation
• Whisk or wooden spoon

Step-by-Step Amazake Recipe

Step 1: Cook the Rice

Rinse 200g of short-grain rice until the water runs mostly clear, then cook it using your preferred method with slightly more water than usual — you want a soft, slightly porridgy consistency (think congee-adjacent, not fluffy steamed rice). Allow it to cool to 60°C (140°F).

Step 2: Prepare the Koji

If using dried rice koji, crumble it into individual grains with your hands. If using fresh koji, simply break apart any clumps. No cooking or soaking is needed.

Step 3: Combine and Check Temperature

In your fermentation vessel, combine the cooked rice with 400ml of warm water and the crumbled koji. Mix thoroughly. Check the temperature — it must be between 55°C and 60°C (131–140°F) to activate the amylase enzymes without destroying them.

Step 4: Ferment for 8–12 Hours

Transfer your mixture to your fermentation setup:

• Rice cooker: Set to "Keep Warm" mode with the lid slightly ajar to prevent overheating (keep the lid cracked with a chopstick).
• Yogurt maker or Instant Pot: Use the yogurt setting at 60°C.
• Slow cooker: Set to "Low" and monitor temperature with a thermometer hourly.
• Insulated cooler: Fill with your mixture, wrap in towels, and check temperature periodically.

Stir every 2–3 hours to ensure even fermentation and consistent temperature. After 8 hours, taste it. You should notice a distinct sweetness developing. Continue up to 12 hours for a sweeter, more concentrated result.

Step 5: Finish and Store

Once your amazake reaches your desired sweetness level, heat it gently to 70°C (158°F) and hold for 5 minutes. This stops enzymatic activity, locks in your sweetness, and extends shelf life.

Blend it smooth with an immersion blender for a creamy drink, or leave it chunky for use as a cooking ingredient or porridge topper.

Store refrigerated in a sealed jar for up to 1 week, or freeze in portions for up to 3 months.

Ways to Use Amazake

Amazake is far more versatile than most people expect:

• Hot drink: Warm gently and serve with fresh grated ginger in winter
• Cold drink: Blend with ice for a refreshing summer smoothie base
• Natural sweetener: Substitute amazake for sugar or honey in baked goods, marinades, and salad dressings
• Marinade: Use to tenderize and naturally glaze fish, chicken, or tofu
• Porridge or oatmeal topper: Spoon directly over your morning bowl
• Baby food: Thinned amazake is a traditional first food in Japan (always confirm with your pediatrician)
• Cocktail mixer: Pair with yuzu juice and sparkling water for a sophisticated non-alcoholic spritz

Frequently Asked Questions

Does amazake contain alcohol? Koji amazake made with rice and rice koji contains no measurable alcohol. The fermentation is purely enzymatic — amylases converting starch to sugar — with no yeast-driven alcohol production. Sake lees amazake, however, may contain up to 1% ABV and should be avoided by those abstaining from alcohol.

Can I use dried rice koji instead of fresh? Yes, dried rice koji works well and is far more widely available outside Japan. The enzymatic activity is slightly reduced compared to fresh koji, so you may want to ferment on the longer end (10–12 hours) and ensure your dried koji is relatively fresh (check the production date). Brands like Marukome and Cold Mountain are reliable options available online.

My amazake doesn't taste very sweet. What went wrong? The most common culprits are: the mixture was too hot when koji was added (killing the enzymes), the fermentation temperature dropped too low during the process, or the fermentation time was too short. Try extending fermentation by 2–3 more hours while maintaining 55–60°C. If it still lacks sweetness after 12 hours, the koji enzymes were likely damaged by heat.

Can I make amazake without a thermometer? Technically yes, but it is genuinely not recommended. Precise temperature control is the single most important variable in amazake fermentation. A basic instant-read kitchen thermometer costs under $15 and will make the difference between a beautifully sweet amazake and a pot of unsweetened rice porridge. Consider it essential equipment.