Sake Brewing: Where Japanese Tradition Meets Modern Measurement

At first glance, it seems deceptively simple: rice, water, koji, and yeast. Yet behind every bottle lies a brewing process unlike those used in wine, beer, or most spirits. 
Sake is often called rice wine, but this description is misleading. Wine begins with grapes that already contain fermentable sugars. Rice, however, offers almost no fermentable sugar. Instead, it consists primarily of starch. This is where koji enters the picture. Koji is steamed rice that has been inoculated with the mold Aspergillus oryzae. During its growth, the mold produces powerful enzymes that continuously break the rice starch into fermentable sugars. At the same time, yeast consumes these freshly produced sugars and converts them into alcohol.

This remarkable process is known as multiple parallel fermentation – a simultaneous conversion of starch into fermentable sugar and sugar into alcohol. It is one of the defining characteristics of sake and is rarely found in any other major alcoholic beverage. 

Master Your Sake Production: Track Fermentation, pH, and ABV with EasyDens, SmartRef and pH2Go

For brewers, this also means that fermentation behaves very differently from what they may know from beer or wine. Understanding what happens throughout fermentation is essential for producing consistent, high-quality sake. Monitoring fermentation progress, verifying pH, and measuring ABV during fermentation and of the finished product all provide valuable insight into the brewing process.

With EasyDens, SmartRef, and pH2Go, these measurements can be performed quickly and easily throughout production.

Turning Our Lab into a Sake Brewery

Reading about sake is one thing, watching the process unfold yourself is something entirely different. Curious to see this unique process firsthand, we turned part of our lab into a small sake brewery and brewed our own batch. Along the way, we monitored the fermentation with EasyDens and pH2Go to track how the sake evolved from day to day. Once fermentation was completed, we measured the final ABV using the Alcohol Meter.
Since this was our first attempt at sake brewing, we kept things intentionally simple. Instead of producing our own koji, we used ready-made Kome Koji, allowing us to focus on the fermentation itself.

Ingredients:

• 3.78 L filtered water
• 400 g Kome Koji (koji rice)
• 1.5 kg steamed rice
• 4 g Lalvin EC-1118 champagne yeast
  

The Brew Begins – Preparing the Rice

We steamed 1.5 kg of rice until fully cooked while maintaining a firm texture. After cooling, the rice was mixed with the Kome Koji.
The rice-koji mixture was then transferred into a fermentation vessel and combined with the filtered water. Once the mixture had cooled to the appropriate pitching temperature, we added Lalvin EC-1118 champagne yeast.

Before yeast was added, we recorded our first measurements to follow the fermentation progress.

• EasyDens:
  • 5.8 °Baumé (-56 SMV@15; 1.041 SG 20/20)
• pH2Go:
  • pH 4.40
    

By comparing the initial and final EasyDens values, we can clearly see whether fermentation has progressed as expected: a drop in density indicates that sugars have been converted into alcohol and helps identify a successful fermentation or a potential fermentation stop.

Fermentation in Action – Following the Fermentation Day by Day

Although traditional sake is often fermented at relatively low temperatures, our laboratory trial was carried out at room temperature over approximately two weeks.
Throughout the experiment, we monitored Baumé and SMV@15 with EasyDens and regularly checked pH using pH2Go. Instead of simply waiting until fermentation was finished, we could observe how sake evolved day by day in the Wine Meister mobile app.

The End of Fermentation

Once fermentation was complete, we separated the liquid from the rice solids using a sieve.
By the end of fermentation, the measurements had changed significantly:

• Final value with EasyDens: 
  • 10.6 °Baumé (8 SMV@15; 0.995 SG 20/20)
• Final pH value with pH2Go:
  • 4.08

The decrease in density from 1.041 to 0.995 SG indicates substantial conversion of fermentable sugars into alcohol, confirming that our sake fermentation experiment was successful and progressed as expected. 

Important to know: What pH Reveals During Fermentation

pH tells us whether fermentation stays healthy.
A slightly acidic environment promotes yeast activity while suppressing unwanted microorganisms, making pH an important process parameter during sake production.
Throughout our experiment, the pH gradually decreased from 4.40 to 4.08, remaining within the expected range for sake fermentation.

Determining the Final ABV with the Alcohol Meter

After two weeks of patient waiting, it was finally time for the moment of truth. Using the Alcohol Meter, we determined the alcohol content directly from the finished sake without distillation.

Important to know:

Finished sake contains alcohol, residual extract, and many other dissolved compounds. Density alone cannot distinguish between these components. This is where the Alcohol Meter comes in. By combining density and refractive index measurements, the Wine Meister app can determine ABV directly from the sample.
 
The measurement workflow is very straight forward:

• Start the Wine Meister app and connect the Alcohol Meter. 
• Draw the sample carefully from the fermenter without disturbing the sediment. Fill the syringe carefully, avoiding air bubbles.
• Degas the sample.
• Measure the sample near room temperature for the most consistent results.
• Place the sample first on the SmartRef prism, then use the same filling for the EasyDens and keep the syringe connected.
• Choose “Sake” and start the measurement.
  

Within only a few seconds, the Wine Meister app displays the final ABV of the sample.

To our experiment: our first laboratory-brewed sake reached an ABV of 11.2 %v/v.

And, perhaps most importantly, our first homemade sake turned out to be surprisingly delicious, too.

Ancient Craft. Modern Insight.

Brewing sake is a fascinating reminder that centuries-old craftsmanship and modern technology are not opposites, they complement each other perfectly.
The traditional process remains unchanged. Rice is still transformed by koji, yeast still performs its remarkable work, and patience remains one of the brewer's most important ingredients.
What modern measurement adds is understanding.
By following density with EasyDens, monitoring fermentation health using pH2Go, and determining ABV directly with the Alcohol Meter, brewers gain insight into every stage of sake production.
The result is not only better process control and improved reproducibility – it is also a deeper appreciation for one of the world's most extraordinary fermentation processes.