In this blog post, let’s explore the process behind making soju—a drink familiar to us all—and examine the principles of distillation, which lies at its core, to understand how it increases the alcohol content of the liquor.
How did soju become a global beverage?
There’s something truly special about enjoying a glass of soju late at night with an old friend. Its distinctive, slightly tingling flavor has garnered a huge following not only in South Korea but around the world. In particular, the soju brand Jinro was named the world’s best-selling distilled spirits brand based on 2025 sales figures and maintained its position as the global sales leader for the 25th consecutive year in 2026. In 2025 alone, global sales of JINRO reached 94.5 million cases (based on 9-liter units). As such, soju is no longer a drink consumed solely in South Korea but has established itself as a global distilled spirit. Perhaps this is why people often say that when it comes to Korean alcohol, soju is the first thing that comes to mind.
Soju belongs to the category of distilled spirits. Distilled spirits are beverages produced by subjecting fermented beverages—made from ingredients such as grains or fruits—to a distillation process in order to increase their alcohol content. While the alcohol content of soju varies depending on the product and manufacturing method, the diluted soju we commonly encounter is made by mixing distilled alcohol with water to achieve the desired alcohol content. Traditionally distilled soju is produced by directly distilling fermented liquor to obtain a high-proof base spirit. So, what exactly is distillation—the process that plays a key role in making the soju that has captivated Koreans for so long?
What is the principle behind distillation?
Distillation is a method of separating substances that are mixed together. The key property utilized in this process is the “boiling point.” We all know that water boils at approximately 100°C. Similarly, each pure substance has a specific temperature at which it boils, known as its boiling point. However, in a solution where different substances are mixed—such as water and ethanol—the boiling point is not fixed at a single, constant value as it is for pure substances; rather, the boiling behavior varies depending on the composition of the mixture. Distillation takes advantage of precisely this difference. Since the boiling point of water is approximately 100°C and that of ethanol is approximately 78.4°C, ethanol vaporizes more easily than water under the same conditions. Therefore, when a mixture of water and ethanol is heated, the proportion of ethanol in the vapor can become higher than that in the liquid as they transform into gas.
To separate a solution of water and ethanol by distillation, the mixture must first be heated. If, while boiling the mixture, all the ethanol vaporized and the water remained in liquid form, it would be a simple matter to collect only the ethanol vapor at its boiling point. However, separating the solution in reality is not that straightforward. Since water and ethanol are mixed together, the vaporization of one substance does not mean the other remains entirely in liquid form. When the mixture is heated, ethanol vaporizes more easily than water, but water also turns into a gas. Ultimately, the compositions of the liquid and gas phases differ during distillation, and this difference can be used to increase the concentration of ethanol.
What changes during the distillation of water and ethanol?
Let’s take a closer look at the principle of distilling a solution of water and ethanol. It is easier to understand how distillation works by considering both the composition and temperature of the mixture. As the composition of the mixture changes, so does its boiling point, and the composition of the vapor produced during boiling also changes.
It is particularly important to note that the resulting vapor contains a higher proportion of ethanol. Therefore, distillation is not simply a matter of boiling the liquid; the key is to cool the resulting vapor back into a liquid, thereby obtaining a liquid with a higher ethanol concentration.
Let’s consider a simple example. Imagine the initial composition of the mixed solution as a single point; if this solution is continuously cooled, it eventually enters the liquid phase. This is the result of lowering the temperature of the gas to transform it into a liquid. Conversely, if the temperature of the mixed solution is raised until it reaches the boiling point, both liquid and gas coexist. At this point, the compositions of the liquid and the gas produced from it are different. Since ethanol is more volatile than water, the gas contains a higher proportion of ethanol than the liquid. Therefore, if you collect the gas produced from the liquid separately and then cool it again to turn it back into a liquid, you can obtain a liquid mixture with a higher ethanol concentration than the original mixture. By repeating this process in multiple stages, you can further increase the ethanol concentration.
However, simply repeating distillation of a mixture of water and ethanol does not allow you to make the ethanol infinitely pure. At a specific composition, water and ethanol form a special state known as an azeotropic mixture; at this point, the compositions of the gas and liquid become identical, making further separation difficult through simple distillation alone. The azeotropic composition of ethanol and water is approximately 95.6% ethanol by mass, and at this point, concentration through distillation reaches its limit.
So how is soju made?
Now let’s take a closer look at the soju production process. First, grains or starchy raw materials are fermented to produce an alcoholic beverage. When this fermented liquid is distilled, the property that ethanol vaporizes more easily than water is utilized to obtain a distillate with a high concentration of ethanol. The purpose of the distillation process is not to convert the entire liquid into a gas all at once. The key process involves heating the mixture to produce vapor containing a relatively high concentration of ethanol, collecting that vapor, and then cooling it back into a liquid. The distillate obtained in this way has a higher alcohol content than the original fermented liquid.
In the case of traditional distilled soju, the fermented liquor is distilled to obtain a high-proof base spirit, and water is then added as needed to adjust it to the desired alcohol content. The diluted soju we commonly drink is made by diluting distilled spirits with water and adjusting the product’s flavor and alcohol content using sweeteners and other ingredients. Therefore, not all soju currently on the market is produced by distilling low-proof fermented liquor multiple times to directly create a beverage with an alcohol content of approximately 20 degrees. The key lies in obtaining distilled spirits—or a distilled base liquor—in which ethanol has been concentrated through distillation, and then mixing in water to achieve the appropriate alcohol content and flavor, depending on the product type and manufacturing method. Although the alcohol content and manufacturing methods of soju have varied over time and by product, the fact that distillation is the fundamental principle for increasing ethanol concentration remains unchanged.
How is distillation utilized in our daily lives?
The advantage of distillation is that it separates the components of a mixture by utilizing differences in boiling points and volatility. Therefore, distillation is not only used in the production of alcohol but is also utilized in various aspects of daily life and industry. In the petroleum industry, distillation is used to separate the various hydrocarbons found in crude oil into their individual components. When crude oil is heated, its components vaporize at different rates, allowing for the separation of various petroleum products. Additionally, by heating contaminated water to produce steam and then cooling it, water can be separated from other components; thus, distillation is also used as a method for purifying water.
The same basic principle applies whether you’re making a glass of soju or separating complex substances in a large industrial facility. It involves collecting the desired components by taking advantage of the fact that different substances have different vaporization and liquefaction properties. From sweet and smooth soju to massive industrial sites, distillation is used in every aspect of human life. Although it may seem simple, isn’t it an important technology that precisely harnesses the properties of substances?
