Course:FNH200/Projects/2022/Soju

Andong Soju (Traditional)

Soju (燒酒) is an alcoholic beverage that originated in Korea. Traditionally, soju was distilled from grains and had high alcohol contents of over 40%. Though in modern times, soju is often much more diluted, often bottled at 13-20% alcohol. Soju is often represented by the iconic green bottle, and has gained global popularity thanks to brands like Chamisul and Chum Churum. Today, soju made using traditional methods and kept at high alcohol contents is called traditional soju or distilled soju, and is exemplified by Andong Soju.

Traditional Method of Manufacturing

Dried Nuruk Used in Soju Fermentation

Soju is a distilled spirit traditionally made from fermented grains. To make Soju, the first step is to combine Nuruk, a fermentation starter made from ground wheat, with water. When the mixture has reached the desired consistency, it is placed into a cloth-lined container and compacted into a mold to create wheat cake. The wheat cake is then removed from the mold and set aside to ferment so that yeast and other microorganisms can grow. This process, which takes around three weeks, solidifies the cake by removing the moisture. After this period, the disc of Nuruk is mashed in a mortar until powdery.

Meanwhile, white rice is steamed in large batches and allowed to cool to the proper temperature.This stage is crucial because if the rice is too warm, the soju may taste sour or bitter. When the rice has cooled completely, it is combined with crushed wheat and a small amount of water to create a somewhat dry mash. After being stirred, the mixture is then poured into a crock or other brewing vessel and let ferment for roughly 12 days.

When the fermentation process is finished, the mixture is strained through cheesecloth or linen into jars. The resulting white liquid is what’s called Makgeolli, another Korean drink. But to make soju, this liquid will still undergo more processes. The liquid will split into two layers after a few days, and the combined structure is referred to as "Wonju." In the past, separate classes in Korean society were assigned to different layers of liquid.

The upper part is a golden, clear liquid known as "Cheongu" or "Yakju," which the Yangban, a wealthy class of nobility, consumes. The lower part is a white, hazy combination known as "Takju" made of rice sediments and utilized by commoners and farmers. They diluted this with water to produce their Makgeolli.

Only the Cheongu is siphoned for Soju, put in the Sojugori (a two-story distillation apparatus with a pipe connected), and then boiled.To prevent vapor from escaping while the liquid is boiling, the spaces are filled with wheat dough. Following distillation, Soju is aged in vats or barrels before being finally bottled.

Distilled Soju was traditionally made with rice, but during the Korean War, when rice was banned, most soju producers were forced to switch to alternative starches like wheat, sweet potatoes, and tapioca.

Modern Method of Manufacturing

The modern method of manufacturing soju originated in Pyongyang in 1919, and spread to Inchon and Pusan. Originally, soju was made from conventional malted wheat (heukguksoju). Beginning in 1952, Soju started being produced using less expensive imported molasses. After the government's 1965 food policy outlawed the use of grain in the production of alcoholic beverages, the difficult, time-consuming process of distilling pure rice wine, with its distinctive bouquet, has completely disappeared. Sweet potatoes, molasses, tapioca, and other ingredients have all been used to dilute the current soju distillation process.

Large vacuum distillation units or copper pot stills are used in modern soju production to distill the liquid. Following distillation, the soju is aged in vats or barrels before being finally bottled. To lower the soju's alcohol concentration, some manufacturers add more sugar, flavorings, or water.

Steps

1. White rice is fermented and distilled, and raw Soju liquid and spirit are combined in a volume ratio of 1:2 to 1:1 to create raw liquor liquid;
2. Adding water to the raw liquor liquid to dilute with a 25–50 volume% alcohol concentration;
3. Adding activated charcoal in 0.05-0.20%(w/v) to remove odor for 2-6 hours;
4. Filtering. The additive may be included either before or after the filtration step. Sucralose, oligosaccharide, sorbitol, xylitol, erythritol, alanine, glycine, or aspartame are among the additives.

Role of Food Science in Soju Production

Fermentation Chemistry:

Like all alcoholic beverages, fermentation is the biochemical process responsible for the presence of ethanol in the drink. Fermentation is an anaerobic process conducted by yeast, a type of fungi that is able to convert glucose into ethanol and carbon dioxide through the chemical equation:

${\ce {C6H12O6->2C2H5OH + 2CO2}}$

However, the grains used to make soju do not naturally contain large amounts of glucose. Therefore, nuruk is added to kickstart the fermentation process. In addition to providing the yeasts Pichia and Saccharomyces that are necessary for fermentation, nuruk contains a variety of molds, namely Mucorales which produce protease, and Aspergillus which produce amylase.

Protease:

Protease is essential in fermentation as it is able to break down larger protein structures into free amino acids that each contain an end with an exposed nitrogen molecule. This increase in free amino nitrogen has been shown to aid yeast’s breakdown of glucose, therefore significantly increasing the ethanol yield in the final product.

Amylase:

Amylase is even more important in the treatment of grains as it breaks down long polysaccharides such as starch into monosaccharides such as glucose. This process provides the essential reactant outlined in the fermentation equation for yeast to begin creating ethanol.

Distillation:

Most often, yeast produces alcohol as a toxin to reduce competition with other microorganisms. However, if the alcohol concentration in the environment gets too high, the yeasts that produce the alcohol cannot survive either. Therefore, the natural alcohol percentage of drinks almost never exceeds 20%. In addition, undesirable substances such as methanol that may be foul or toxic can be found in freshly fermented beverages. In order to have a higher-proof liquor that is clear and safe to drink, distillation is used. Distillation comes from the Latin word “destillare” meaning “to drip” and does exactly that. In the distillation process, the fermented beverage is heated so vapors more volatile than water can be released, which includes methanol, alcohol, and many aromatic compounds that differ in their boiling points. Distillery machines are then able to use the time and temperature to release the undesirable compounds including methanol (highly volatile, lower boiling point) and fusel oils (less volatile, higher boiling point) while condensing ethanol vapors and storing them in a separate container. The concentrated ethanol is then diluted to their respective alcohol content.

Charcoal Filtration:

According to their official website, Jinro soju is filtered through bamboo charcoal for a “fresher taste”. But why is that? Even though the exact chemicals removed through charcoal filtration was not listed, it is known that carbon can be used for water purification. Carbon, in the form of graphite (charcoal) has a very large surface area. This gives it a very large van der Waals force and is able to attract non-polar organic molecules, which includes certain congeners, byproduct of fermentation that was not removed during distillation, that contributes to the harsh taste associated with alcohol drinking.

Food Additives and Different Flavors of Soju

Some Varieties of Artificially Flavored Soju

Soju can contain a few additives (depending on flavor) that are used in order to get the distinct smooth flavored taste. Artificial flavors are used as an ingredient in many fruit flavored soju brands because of the lower overall cost of making the flavor and the consistency that it provides its products. Both leading brands of soju, Jinro and Chum Churum, use artificial flavors to get the desired taste of fruit in their products. Jinro has nine flavors, while Chum Churum has six. Even though the exact list of all additives found in soju are not disclosed to the public, these are some artificial flavorings known to be used in soju production:

Citric Acid

Citric acid is a weak organic acid that occurs naturally in citrus fruits. They have the chemical formula ${\ce {C6H8O7}}$ and act as a flavor enhancer and chelating agent.

Esters

Esters are the result of the formation of condensed reactions between carboxylic acid and alcohol i.e. ${\ce {RCOOR^'}}$. They provide a lot of the aromas we associate with fresh fruit, and serves to create the fruity flavor in soju. For example, the ester named Octyl Acetate (${\ce {CH3COOC8H17}}$) is a major component responsible for the orange flavor that can be found in orange soju.

Fructose

High Fructose Corn Syrup (also known as glucose-fructose, isoglucose, and glucose-fructose syrup, HFCS) is made by converting glucose contained in corn syrup made from corn starch into fructose using enzymes. The sweetness level of fructose sugar depends on the proportion of fructose in it, but fructose sugar is sweeter than glucose or sugar by itself. If you look at the results of comparing the sweetness, fructose is usually about 200% sweeter than glucose and about 140% sweeter than sugar. Therefore, HFCS with a high proportion of fructose is inevitably sweeter than glucose and sugar. HFCS is also a type of carbohydrate. The number immediately following HFCS, the English abbreviation for high fructose, indicates the percentage of fructose. For example, HFCS 55 is 55% fructose and HFCS 42 is high fructose containing 42% fructose. HFCS 55, which is often used, is cheaper than sugar and has the advantage of being more soluble in water than sugar, so it is often used to make soju and soft drinks.

Thaumatin

A protein sweetener is obtained by extracting and purifying the fruit of Thaumatococcus daniellii, which grows wild in the forests of tropical rainforests in Africa.

It is a light brown-gray brown powder, flakes or lumps, without odor or bitter taste, and has a strong refreshing sweetness. It is easily soluble in water and is stable under high heat or acidic conditions. Contains all amino acids except histidine. It is a high-sweetness sweetener of about 5,000-8,000 times that of sugar and has 2,500-3,000 times of sweetness compared to 8% sugar. Compared with other sweeteners, there is no bitter aftertaste or unpleasant taste, and it has a refreshing sweetness. It tastes sweeter than sugar but lasts longer. It is very stable to heat and has an isoelectric point of pH 11.5 to 12.5 and is stable even in acid, so separation, precipitation, and cloudiness do not occur under acidic conditions. The allowable daily intake (ADI) has not been established.Thaumatin has a flavor-enhancing effect in addition to providing sweetness and has an effect of enhancing the natural flavor of the food material itself, such as added spices, spices, and seasonings. In particular, as thaumatin is a macromolecule, it has both cations and anions in the molecule, so the salty anion combines with the cation in the tomatine molecule to remove the salty taste. It is used as a sweetener and flavor enhancer, which improves the flavor of soju, relieves unpleasant bitterness or astringency, and removes the fishy taste of vitamins and minerals.

Enzymatically Modified Stevia

Enzyme-treated stevia is a raw material used to sweeten. Stevia's stevioside has zero calories and is a very sweet ingredient (see below for additional information on stevia). However, since it has a strong bitter taste, enzyme-treated stevia is enzyme-treated to remove the bitter taste. It has a refreshing sweetness compared to other sugars.

Stevia

To be precise, it is the name of a perennial plant in the Asteraceae family. It is water-soluble and contains stevioside, which is 300 to 900 times sweeter than sugar of the same weight. This ingredient called stevioside has the advantage of creating a sweet taste that is not absorbed by the body during digestion. On the other hand, it is characterized by a bitter aftertaste. However, this bitter taste can be significantly reduced through processing. (Processing: Enzyme-treated stevia is the treatment of stevia extract with α-glucosyltransferase. In this way, α-glucosylstevioside can be obtained by attaching glucose) .

Possible Exam Question:

Which of these processes is not essential for the production of ethanol from grains?

A: Protease enzymes breaking down proteins into free amino acids.

B: Lipase enzymes breaking down fats into fatty acids

C: Amylase enzymes breaking down polysaccharides into monosaccharides

D: Yeast converting glucose into ethanol and carbon dioxide

Correct Answer: B

We believe this is an appropriate question to include on the final exam as we have been familiarized with the three enzymes involved in the breakdown of fat, protein, and carbohydrates. We have also learned about the basic properties of yeast and fermentation. This question tests the student's knowledge of the properties of these enzymes, the basic composition of grains, and the roles of the three macronutrients in the fermentation process.