What Happens to All the Food Waste on a 4,300-Passenger Cruise Ship?

Cruise writer Fran Golden headed into the belly of the recently launched “Sun Princess” to see how cruise ships are changing the way they process uneaten leftovers.

Princess Cruises' 4,300-passenger "Sun Princess" docked in Europe with rolling hills and a city in the background

Biodigesters and food dehydrators have been installed on Princess Cruises’ newly launched Sun Princess to process food waste in a more eco-friendly way.

Courtesy of Princess Cruises

In a lower deck aboard the 4,300-passenger Sun Princess, the largest and newest ship in the Princess Cruises fleet, I’m touring a back-of-house area where giant stainless steel “stomachs” are grinding and using bacteria to digest food waste, turning thousands of pounds of leftovers into a thick, bio-friendly opaque slurry. Meanwhile, another big machine, referred to as the “Hungry Giant” by crew, is taking bones, fruit rinds, and other objects that would destroy your home garbage disposal, dehydrating them, and turning them into what looks a lot like coffee grounds.

The smells in the disposal areas are what you would expect of what’s left in the garbage after guests have had their fill at the ship’s 30 restaurants and bars. The sounds are a lot like a coin laundry. Together, the innovative technologies are dramatically reducing the impact of food waste on the ocean and what is offloaded to landfills.

Reducing food waste starts with what’s on the cruise ship menu

Princess Cruises’ parent company, the nine-brand Carnival Corporation, is focused on reducing food waste as part of its sustainability efforts—a common effort among cruise lines, which are collectively aiming for the same ambitious climate goals over the coming years. Aggressive actions begin with minimizing the sheer amount of leftovers, including using AI technology to monitor and analyze guest dining trends. Crew members also manually keep track of and report what they see getting left behind, so that unpopular food items might be taken off menus.

Sami Kohen, vice president of food and beverage for Princess Cruises, who, like me, was aboard the Sun Princess in late April for a cruise from Rome to Barcelona, says eliminating food waste begins with which foods are served and how.

An empty Alfredo's Pizzeria, a casual dining venue on the "Sun Princess," with an order counter and a dining table and chairs

The hope is that having tempting food options throughout the ship reduces waste because passengers are more likely to clean their plates.

Courtesy of Princess Cruises

On the new ship, which features a stunning glass dome above an indoor/outdoor pool and an intimate theater for circus performances, as well as an entire family-friendly amusement area on top, guests can dine on designer sushi and beef cuts in innovative, specialty restaurants (for an added fee). Or they can indulge on dining room menus that have been revamped in collaboration with chefs from the Culinary Institute of America (with a team of chefs from the prestigious culinary school coming aboard to train the galley team in preparing the dishes). There’s also an all-American diner that serves all-day breakfast, among numerous other options.

Kohen contests that having tempting food styles and cuisines throughout the ship reduces waste. “You eat what you desire at the moment,” Kohen says.

Behind the scenes, waitstaff and kitchen crew separate what is leftover from meals into color-coded containers (veggies here, meat with bones there), which are then weighed so that food waste amounts can be tracked. Says Kohen, “On this ship, we are doing more to reduce food waste than any hotel in Las Vegas.”

New cruise ship food waste disposal methods

With thousands of passengers and crew aboard, there are, of course, leftovers, and that is where the innovative biodigester machines come into play. Carnival Corporation officials first spotted the machines being used in hotels and event spaces a few years ago and realized that they could be adapted for use at sea.

A room with several large mirror-walled biodigesters on the "Sun Princess"

A room of biodigesters on the Sun Princess

Photo by Fran Golden

The biodigesters—there are 13 on Sun Princess alone—work like human stomachs, using a natural process involving bacteria to break down uneaten food, both reducing the original volume to just a small fraction and reducing the demand on the ocean in terms of food waste decomposition. The company also replaced plastic balls that were used to grow and spread bacteria for the digestion process with the more natural alternative of peach pits. The resulting mixture is mostly decomposed when it is released at sea—as allowed by international law, cruise ships may dispose of ground food waste at sea, no closer than 12 miles from land.

The machines digest food 24 hours a day. “The bellies need to be fed all the time or they do not work, like your own stomach,” says Biagio Del Vecchio, environmental officer on the Sun Princess.

For solid foods that are harder to break down, such as bones, animal fats, and skin from fruits and vegetables, Carnival Corporation recently added dehydrators—there are more than 60 in the Carnival fleet of over 85 ships. The dehydrators use heat to remove excess water from leftover food, producing a mostly dry mass that looks like coffee grounds, which can be easily offloaded on shore. Carnival Corporation says the dehydrators can reduce the amount of food waste offloaded by up to 90 percent. While the odorless grounds are currently sent to landfills, there are plans to see if they might be repurposed by other companies, perhaps burned as a sustainable energy source or used as a fertilizer.

A sign with photos of food indicating what can and can't be processed by the biodigester

A sign indicating what can and can’t be processed by the biodigester

Photo by Fran Golden

The results

With the food waste management technology and other measures, Carnival Corporation says it has accomplished a more than 40 percent reduction in food waste per person, relative to a 2019 baseline, and is already ahead of its 2025 goals. The company is targeting a 50 percent reduction per person, relative to the 2019 baseline, by 2030.

The Sun Princess, which is sailing the Mediterranean in summer and the Caribbean in winter, is also the first in the Princess Cruises fleet to operate on liquified natural gas (LNG), considered the cleanest-burning fossil fuel currently available at scale. The ship is also adaptable to alternative fuels as they become available, showcasing that progress is definitely possible, including on some of the world’s largest cruise ships.

Fran Golden is an award-winning travel writer who has sailed on some 170 ships to destinations around the world.
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