Cassis Day (Kashisu no Hi)

What Is Cassis Day?

July 23 is "Cassis Day" each year, established by the Japan Cassis Association in 2006 (Heisei 18). The date is based on the fact that cassis harvests typically peak around "Taisho," one of the 24 traditional seasonal divisions, which usually falls around July 23. The day is meant to highlight the excellent nutritional value of cassis (blackcurrant), grown in cool regions such as Northern Europe and Aomori, particularly for eye care and antioxidant benefits — both common concerns for modern lifestyles.

The "Miracle Fruit" of European History

Cassis has long been valued in Europe both medicinally and as food.

• Medicinal use in 18th-century France: In 18th-century France, cassis was prized as a "cure-all" and was widely cultivated, including in monasteries. This laid the cultural and practical groundwork for its later use in French cuisine and liqueurs such as crème de cassis.
• Cultivation begins in Aomori: Cassis saplings were introduced to Japan from Germany around 1965, and cultivation took root in Aomori Prefecture, where the climate proved well-suited. Today, Aomori City is Japan's largest producer, and its harsh winters help develop the deep color and beneficial compounds in the fruit.

The Science of "Cassis Anthocyanins"

The deep purple pigment in cassis carries scientific evidence that sets it apart from other berries.

• Unique compounds D3R and C3R: Cassis contains "delphinidin-3-rutinoside (D3R)" and "cyanidin-3-rutinoside (C3R)" — types of anthocyanins not found in bilberries. These have a strong effect on improving peripheral blood flow, contributing to eye focus adjustment and easing muscle tension.
• Support for dark adaptation: Dark adaptation refers to how your eyes adjust to dim light. Cassis anthocyanins help support the regeneration of rhodopsin, a pigment in the eye, which has been shown to help maintain night vision and ease eye fatigue in the evening.

Fun Facts About Cassis

• Vitamin C content: Cassis contains roughly three times the vitamin C of oranges and about four times that of blueberries. It's also rich in vitamin E, an antioxidant, giving it a role as a kind of "edible sunscreen" that helps care for UV-damaged skin from within.
• Why winter cold is necessary: Cassis has a physiological trait called "dormancy break," meaning it won't sprout in spring unless it experiences a certain period of cold during winter. This harsh cold acts as a trigger for concentrating polyphenols in the fruit.
• The birth of the "Kir" cocktail: The mayor of Dijon, France — a man named Kir — created a cocktail by mixing local white wine with cassis. This became a key moment in spreading the flavor of cassis around the world.
• Antibacterial action against H. pylori: Recent research suggests that compounds in cassis may help suppress the activity of H. pylori, the bacteria linked to increased stomach cancer risk — a promising area for digestive health research.

Tips for Enjoying Cassis Day

• To mark July 23, try incorporating cassis juice or jam into your diet. The deep purple pigment can help promote peripheral blood flow, easing the eye strain that comes from desk work and smartphone use.
• Check the ingredient list when buying drinks or supplements. Comparing the specific compounds versus blueberries (cassis's unique anthocyanins) is a great way to make a more informed choice.
• Beat the summer heat of "Taisho" with a chilled cassis soda. The citric acid in cassis helps with the metabolism of fatigue-related substances, giving your body a science-backed boost during the hottest days.
• Take a moment to focus on your eye health. Look at something far away once an hour, avoid your phone in dark rooms — let Cassis Day be the trigger for some concrete self-care for your eyes.

A Deep Purple Drop of the Earth's Vitality Brings Clarity to Your Eyes and Insight for Tomorrow

July 23 is a day to appreciate the resilience of cassis, which reaches its peak in the hottest part of the year. Each berry, having survived the harsh winters of Northern Europe or Aomori, carries within it the wisdom needed to endure tough conditions. After months of staring at screens, have your mind and eyes started to feel a little dry and worn out? Today, take time to savor the refreshing tartness and rich aroma of cassis. As the tension behind your eyes eases and your vision sharpens, your thinking can move forward more clearly too. Welcome a vibrant summer with this jewel of purple.