Lock Ice Day (Rokku Aisu no Hi)
Food DaysWhat Is Lock Ice Day?
June 9 is "Lock Ice Day" each year. The date comes from a wordplay on "ro(6)kku ai(9)su" ("rock ice"), and the day was officially certified and registered by the Japan Anniversary Association in 2018. The goal is to raise awareness of "Rock Ice," a brand of packaged ice, and to highlight its many uses and value.
What Is "Rock Ice"?
Rock Ice is a brand name owned by Kokubo Ice Co., Ltd., based in Yachiyo City, Chiba Prefecture, and refers to bags of crushed ice. Since its launch in 1973, it has been used in homes, restaurants, events, and many other settings.
- Launch: The "Rock Ice" brand was launched in 1973.
- Trademark: "Rock Ice®" is a registered trademark used as the product name.
- Uses: Commonly used to chill drinks, for outdoor activities, home parties, and more.
The Background Behind Lock Ice Day
The numbers 6 and 9 combine to sound like "rokku" ("rock"), and this wordplay became the basis for the anniversary — an opportunity to raise awareness of Rock Ice itself while also highlighting the broader value of ice as something that "cools." The day is officially registered with the Japan Anniversary Association.
The Social Role of Rock Ice
Far from being "just ice," Rock Ice has established itself as a convenient product for everyday life and a wide range of occasions. Beyond chilling drinks, it's also used for preserving food, beating the heat, and even at sporting events.
Ways to Enjoy Lock Ice Day Intellectually
- Look into the differences between Rock Ice and other types of ice, such as crushed ice or ice-tray ice.
- Explore the science behind why ice is so effective at cooling (latent heat of fusion, specific heat).
- Research how Rock Ice is used in Japanese households and dining culture.
- Compare ice culture and ice-based dishes and drinks across different regions of Japan.
The Everyday Value of "Cooling Things Down"
June 9's Lock Ice Day is a chance to pay attention to something we use casually every day — ice — and learn about the value and history behind it. Since the 1970s, Rock Ice has steadily woven itself into our daily lives, expanding the ways we use it. This anniversary is a good opportunity to reconsider the role that ice itself plays in our lives.