For the longest time, I have known only wine gets better with age, but it appears, soup does too - in Bangkok, Thailand.

When it comes to food, freshness is often a priority for anyone seeking a fine dining experience - or at least trying to avoid a visit to the doctor or free subscription calls with Mother Nature.

However, scouring travel sites on Asian destinations introduced me to Wattana Panich, a Thai restaurant located on Ekkamai Road in Bangkok. Passed down three generations, the eatery is famed for its Beef Brooth noodle soup that has been simmering for 50 years...yep...50 years.

They use a traditional cooking method where at the end of each day, the remaining soup is saved and used as a base for the next day's batch. This practice, known as "perpetual stew," creates a complex and deep flavour profile that develops over time.

The restaurant is a family-run business and a popular spot for both locals and visitors interested in tasting this unique, historic dish.

The restaurant building - plainly decorated, with bare ventilation, exposed concrete floors and a weathered façade - does not appeal much, but the huge number of customers tells a different story.

How is the soup 50 years old? At least, do they clean the pot? - Are some of the questions that bugged my mind as I searched for reviews on the restaurant.

In a previous interview with NPR, owner Nattapong Kaweeantawong explains how it all came to be - and is done - demystifying a misconception held by others regarding its hygiene.

"Lots of people think we never clean the pot. But we clean it every evening. We remove the soup from the pot, then keep a little bit simmering overnight," he explains.

So, the little that is left is what forms a base for the next day's soup. While the soup, entirely, is not 50 years old, the taste is.

"Since my grandfather's time, we've never really had a set recipe about how much of each ingredient to put in. So the person making the soup will constantly have to taste it to know what needs to be added," Nattapong explains.

The third-generation owner reveals that several spices go into the broth, including; cinnamon, garlic, black pepper, cilantro root, and a dozen Chinese herbs, among others. The eatery cooks over 70 kilograms of meat daily.

"To make it tender, we cook the beef for around seven hours. We put the whole thing into the pot so it absorbs all the flavours. Then after three hours, we take it out and cut it into smaller pieces, then cook it for another four hours," Nattapong reveals.

Wattana Panich occupies two floors of the building - which the family bought decades ago. The huge pot - 5 feet in diameter and 2.5 feet deep - conspicuously cooking by the entry attracts revellers to the restaurant.

Nattapong notes that he is privileged his family bought the building since current rent prices along that street are high.

"When I first started in the business, my dad would make the soup and the broth and I would taste it, to understand what the perfect taste is. Nowadays, I can just look at it and know what's missing," he says.

Nattapong's father and mother work at the restaurant, but he calls the shots. One thing is for sure - his father makes the best soup, he admits.

As he continues to grow the business which is a constant for locals and tourists visiting the area, he notes that his daughter has since shown interest in taking over the business from him when the time comes.