Hashira-jochu (a brewing method of sake liquor) (柱焼酎)

"Hashira-jochu" was one of the terms used for traditional manufacturing methods of sake (Japanese rice wine) that existed in the beginning of the Edo Period, which is to add shochu (distilled spirit) or kasudori-shochu (shochu made from sake lees) to moromi (unrefined sake) or newly brewed sake after separation from lees by applying pressure. This technology had been commonly applied to brewing sake until the middle of the Meiji Period when anzen-jozo (safe brewing method) was established.

Source:
This term is found in "Domoshuzoki" (a technical book on brewing sake) which is commonly presumed to have been published in 1687.

In the history of Japanese sake, this book had been an established directory containing the best contents concerning the brew of sake, from the view point of both quantity and quality throughout the Edo Period, despite it was published in the early Edo Period. The writer has not been specified yet, but it is assumed that a sake brewing expert of Konoike school in Itami might have written the book because it contains descriptions about then-current sake brewing technology of the school.

Summary:
According to "Domoshuzoki," sake would "taste hale and hearty, and become robust" by adding shochu spirit to it.
This function of shochu was the reason why it was named "hashira-jochu" (literally, "shochu spirit as a supporting pillar")

The phrase "ashitsuyoku soro" ("become robust") may be understood to imply "rot-resistant" or "become hard to decay." In fact, throughout the Edo Period, brewing of sake was a risky business facing always with possibility of decaying its products, and, therefore, it may be reasonable to consider that shochu spirit was added to sake wine in order to increase its proof and prevent its corruption.

In the history of Japanese sake production, this situation had remained unchanged until early Meiji Period when technology of anzen-jozo (safe brewing) was established. Even in the middle of the Meiji Period, sake breweries were commonly managed on the premise that about ten percent of the brewed sake would become rotten before shipment.

Relationship with modern "alcohol addition":
The phrase "Aji ga shan to si" ("taste becomes hale and hearty") may be read as to imply "its taste becomes tauter "or "it becomes dry.". Accordingly, many informed persons recognize the hashira-jochu as the original form of alcohol addition in the current production process of Japanese sake wine. This represents the viewpoint that "today's alcohol addition is a traditional technology that can be traced back to hashira-jochu."

In other words, it is now viewed that the brewers at that time resorted to shochu spirit that was then high-proof beverage, because they could not produce industrially fermented beverage like today.

On the otherhand, some people are against the above view and insist that "no trace of traditional technology of hashira-jochu can be seen in the current alcohol addition technology."
Their opinion is based on the following reasons:

In the Edo Period, the Japanese sake was far sweeter and heavier compared with the current average refined sake, and its quality resembled today's mirin (sweet rice wine for cooking). Making it "shan-to" (hale and hearty) is different in its meaning from adding another alcohol component to already sufficiently hot Japanese sake of today.

The technology of hashira-jochu, which was originally applied for the purpose of preventing corruption of sake quality, is no longer needed for that purpose in these days when a risk of decaying sake is negligible due to established technology of safe brewage. In fact, current alcohol addition is applied for different purposes.

"Domoshuzoki" started describing how to manufacture high-quality shochu, which would require a lot of expenses and labors if you follow. Therefore, it is not logical to insist that alcohol addition for cost and labor saving is the contemporary version of hashira-jochu described in "Domoshuzoki."

Thus, there exist two contradicting accounts of relationship between hashira-jochu and today's alcohol addition. At the same time, there are some Japanese sake brands like "Kurosawa, Hashira-jochu sikomi" of Kurosawa Brewery in Nagano Prefecture, which is made by blending brewed sake with alcohol of kome-shochu (rice distilled spirit) in the way of hashira-jochu of the Edo Period as written in "Domoshuzoki."