Shochu Aging and Maturation
When comparing spirits to other other alcoholic beverages, the two most distinguishing factors are aging and maturation. For spirits like sherry, brandy and even whisky, aging and maturation are integral steps in the production process because it creates a smoother, more flavorful beverage.
Aging and maturation also play very important roles in the production process of shochu, as it provides another opportunity for flavor to be refined further.
Shochu can be aged and matured using one of three types of containers: earthenware pots, metal tanks, or wooden casks. Each technique adds unique flavor and aromatic properties, which can only be attained through the implementation of aging or maturation.
Earthenware Pot
Earthenware pot aging is the most primitive form of aging and maturing in the shochu industry.
The use of earthenware in the shochu industry, however, is far less glamorous than the earthenware and ceramics that are commonly seen in Japan's art galleries and museums.
Earthenware-aged shochu is typically more gentle and mild than those aged in metal tanks or wooden casks. Earthenware aging is great for taming the usually intense, robust aroma and flavor of sweet potato shochu; leaving a mild and slightly sweet shochu that is easy to drink--even straight. The softening attributes of earthenware also make it the best method for long-term aging. This type of aging usually lasts three or more years depending on the makers desired length of aging.
The construction and material of the pots have profound effects on shochu. The pots are crafted with the inside left exposed and unglazed. The unglazed surface induces oxidation as air and natural minerals fill the tiny pores in the surface.
Another benefit is infrared radiation (also called thermal radiation, or thermal heat), which can be describe as the heat that is absorbed and subsequently stored in a heat-conductive material. The thermal heat found in the pots assist in producing a milder and softer taste, and a far less potent aroma.
Earthenware pot aging is a far more labor-intensive method because the pots are more difficult to maintain than the other aging devices. They are also very large, some as big as 6 feet tall and 5 feet wide. For these reasons, fewer shochu makers are willing to implement the use of earthenware pots for aging or maturation.
Metal Tank
Metal tanks are clearly the most efficient way to age shochu, and are becoming the method of choice in the shochu industry. Typically
constructed of either stainless steel or enameled iron, metal-tank aging preserves the natural flavor and aroma of shochu. This allows the consumer to experience the shochu in its purest state.
The preservation of the raw materials' characteristics is a result of the air-tight seal the metal tanks provide. The inability of outside air to penetrate the tank leads to a lower amount of oxygen infiltration into the shochu, and causes a large amount of water to evaporate during the maturation process. The loss of water leaves only the genuine and pure alcohol, of earthenware pot and wooden cask aging, where the influx of oxygen is encouraged.
In essence, shochu matured in metal containers exemplifies the properties of its raw materials and type of koji. The raw materials and koji type are most significant in determining the characteristics of the final product. Metal-tank aged shochu will possess a full flavor and aroma with a strong resemblance to its main ingredient.