Who knew bananas are much more than a favorite fruit to eat with breakfast cereal or bake into breads and desserts?

At the Ka Mai‘a ‘Ho‘olaule‘a/Banana Festival on Saturday, find out how the fiber of the banana is used in weaving and how its sap can be used as a dye to decorate kapa, among other activities at Waimea Valley.

The second annual ­festival, co-sponsored by Slow Food Oahu, runs from 10 a.m. to 2 p.m., with a special lecture on growing practices at 9 a.m.

A multitude of banana varieties will be available for tasting. Chefs from Koko Head Cafe and Nami Kaze Hawaii and other restaurants will provide samples of banana dishes.

For the first time Wesley Sen, master lauhala weaver and kapa maker for over 40 years, will exhibit an unusual purple banana sap from the fe’i banana tree. He uses it as a dye to print decorative patterns on the Hawaiian bark cloth called “kapa” or “tapa,” as it is known elsewhere in the South Pacific.

Sen said the fe’i plant’s sap oozed out purple only when he first cut off a half-inch deep strip from the trunk; the rest of the sap in the trunk stayed watery-white. He made this discovery when he was stripping the black bark off of the tree to decorate another item.

He can’t promise there will be enough purple sap for all festival participants to use in making a print, but they can see what it’s like, Sen said. There are just a few fe’i trees on Oahu, but Gabe Sachter-Smith, festival co-sponsor, has a small patch of it on his Banana Source farm and gave some to Sen.

The fe’i banana is prolific in Samoa and other parts of the South Pacific. Sen studied under noted Samoan tapa artist Mary J. Pritchard in the 1980s, who told him the purple sap was reserved for tapa made for royalty, Sen said.

Babs Miyano-Young will supervise the banana fiber printing booth; participants can bring their own T-shirt to decorate or purchase a blank T-shirt. Mahina and Cheryl Pukahi will demonstrate lauhala and banana fiber weaving.

A wide variety of banana plants will be for sale, along with banana books and other items.

At 9 a.m., Sachter-Smith will give a one-hour lecture and slideshow on banana culinary lore, botanical history and best growing practices. Be at Waimea Valley by 8:45 a.m. with tickets in hand.

Tickets purchased in advance via Eventbrite.com are $10, or $12 at the door, which will include admission to the entire Waimea Valley. Children under 12 are free.