Ajitama Egg (Nitamago/Ajitsuke Tamago)

The well-loved ajitama, one of the most ramen toppings, has an origin story that might raise a few eyebrows. One theory suggests that its roots trace back to Taiwan. There, a notable dish known as Danzai noodles sometimes comes topped with a boiled egg marinated in soy sauce. Many believe this Taiwanese dish served as the muse for what we now know in Japan as “ajitama.”
While its true origins remain a bit hazy, one thing’s almost certain: Kan Chin Tei (now closed), a ramen joint tucked away in Ogikubo, Tokyo, is credited as the first in Japan to introduce ajitama as a ramen topping. However, it was at another eatery, Chibakiya, where soft-boiled eggs made their ramen debut. The man behind this innovation was a chef (Kenji Chiba) who originally specialized in traditional Japanese cuisine.
Chiba found himself awestruck by Taishoken, a ramen restaurant where people queued up just for a taste of their incredible noodles regardless of the look and atmosphere. At the age of 40, he left his executive chef position and decided to follow his newfound passion for ramen.
Before Chiba, the eggs on ramen were typically hard-boiled or had a heavily seasoned surface. Using the culinary techniques he’d learned from traditional Japanese cuisine, he pioneered the perfect soft-boiled egg, a game-changer in the world of ramen.
Nowadays, you’ll find half-boiled ajitama in nearly every ramen restaurant, but before Chibakiya, this innovation was simply not a part of the ramen scene. Chiba’s contribution was not just an ingredient; it was a transformation of tradition.

You might have noticed that I’ve been using “Ajitama,” “Ajitsuke tamago,” and “Nitamago” to describe this delicious egg dish. So, you’re probably wondering, “What’s the difference?” In short, ajitama is just an abbreviation of ajitsuke tamago, so they’re exactly the same thing. But Nitamago, strictly speaking, is a little different.
Here’s how it breaks down: Ajitama is mostly soft-boiled and flavored by being placed in a container like Tupperware or a Ziploc bag with marinade added to it. Nitamago, on the other hand, starts as a boiled egg, which is then simmered further in a pot with seasoned broth, resulting in a hard-boiled egg. For example, a nitamago would be made by boiling a boiled egg with Kakuni (Japanese braised pork belly) or Oden (Japanese winter stew).
However, the line between the two has become quite blurry these days, and half-boiled eggs also started to be called nitamago. If you google nitamago recipes in Japanese, you’ll mostly find recipes with half-boiled eggs. Perhaps hard-boiled nitamago has fallen out of favor in the face of the popularity of half-boiled eggs in general. So, all in all, it does not really matter which term you use to describe marinated soft-boiled eggs to use for ramen.

When a recipe calls for “sake” on Sudachi, I use pure sake without added salt. Cooking sake with salt requires adjusting the recipe’s salt content. All dishes on Sudachi use drinking sake. For more on sake in Japanese cooking, see the “Sake 101” post by a 30+ year industry veteran.

We usually don’t reheat them as you can risk making the yolk too firm. The ramen egg tends to warm up in the ramen soup. If you really want to reheat them, you can place them in hot water, no warmer than 70C/158F to ensure they don’t start cooking again.

They should be kept in the fridge and eaten within 3-4 days in the marinade or 24 hours once removed from the marinade.

Not only does the marinade lose its flavor after soaking the first batch of eggs, but reusing it increases the risk of bacteria forming. The marinade can only be kept for 3-4 days which means that each batch of eggs will have a shorter life. I recommend making a new marinade for every batch of ramen eggs.