A small pizzeria on Bainbridge Island, Wash., says it's maintaining a piece of Klondike Gold Rush history.

In fact, they "feed it" every night.

Restaurant owner Will Grant says his family has maintained a genuine Klondike sourdough starter which has been alive about 120 years.

"We don't use any commercial yeasts or anything like that — it's the same living organism that we've kept feeding all these years," he said.

Bainbridge Island is a short ferry ride from Seattle, a city with a historical connection to the Klondike. Thousands of prospectors left on ships from Seattle, to attempt the infamous trail of 1898.

Klondike Gold Rush hopefuls lined the Chilkoot Trail on their journey to the Yukon's goldfields in the late 1890s. (E.A.Hegg/National Archives of Canada/)

Grant doesn't know the exact origin of his sourdough, but the family story is that his father obtained the starter through a business partner whose great-grandfather "had come down from the Klondike."

Sourdough was used during the Gold Rush because it travelled well in difficult conditions. It is possible to keep the bacteria alive for decades and there are many examples of starters being used for more than a century.

"It really gives it the flavour of a sourdough baguette. It's chewy but nice and crisp on the outside. It's really a unique flavour," Grant says.

Grant describes his crust as 'more like a French baguette.' (Submitted by Will Grant)

The family's pizza shop is called That's A Some Pizza (try saying it with your best Italian accent). It's a short ferry ride from downtown Seattle. It has been in business 35 years.

Originally the sourdough starter was kept in a mason jar.

In 1984, Grant's father and his friend used it to make pizza in Kingston, Wash. They were inspired to start the business.

Grant has memories of being five years old and tasked with "feeding" the starter. Now having taken over the business, he still does.

Over the years, the starter has grown immensely in size and Grant says it now fills three large plastic vats in the restaurant's kitchen.

A close-up look at the raw sourdough. The restaurant claims to make 900 kilograms of dough a week using a 120-year-old starter. (Submitted by Will Grant)

"In the evening, we'll replenish it with five pounds of water and five pounds of flour. And by the morning, it's grown the point where it can be used again," he says.

The sourdough crust is the foundation for everything the pizzeria makes — except for what's gluten-free.

'Secret' no longer

The pizzeria is proud of its claim to a Klondike connection. Dial the restaurant's number and you might hear a recording of accordion music and a voice proclaiming that the "secret family pizza dough recipe uses a 120-year-old sourdough starter from the Klondike Gold Rush."

He has even taken his sourdough-crust pizza to an international competition in Italy, and recently placed 19th worldwide in the International Pizza Expo in Las Vegas.

Pizza chef (or, 'pizzaiolo') Will Grant (left) says using sourdough makes the pizza chewy and crispy. He's taken his creations to international competitions. (Submitted by Will Grant)

The starter is even destined for a museum. A Belgian company is convinced of the starter's Klondike origin, and has asked to preserve a sample.

Baking research company Puratos helps maintain a "sourdough library" in Belgium, with bacterial samples from around the world. The company says the goal is to "preserve baking knowledge and sourdough heritage."

Grant says a representative from the company is coming to Washington next month to collect four pounds of his starter, to store in its "library."

Grant says he's happy to talk about and share his secret ingredient.

"My mother never marketed it. In 30 years, they never once promoted the fact they used sourdough starter. They thought the idea of 'sour' would scare people off," he said.

"It's been fun for me to be able to share something we've been doing more than 30 years."