What does the term 'Ishobin' refer to?

The term 'Ishobin' refers specifically to a standard bottle size for sake that holds 1.8 liters, which is equivalent to two shaku (or four go) of sake. In the context of sake terminology, this size is significant as it is commonly used for both retail and serving in various settings, representing a traditional container for sake. The Ishobin bottle is distinct from other sizes, making it important for understanding sake retail and production.

The other options, while related to beverage measurements or serving techniques, do not accurately define Ishobin. A unit of wine measure does not specifically pertain to sake or its traditional sizes. Similarly, a traditional sake serving would refer to smaller portions, often served in cups or smaller vessels, rather than a full bottle. Lastly, a fermentation technique would relate to the brewing process rather than to the bottling or serving sizes of sake.