How many times a week do you have to throw away food? How often do you stop and think about why?

By all counts, food waste in the United States is one of the biggest problems facing the industry, Austin-based writer Tom Philpott explained at another SXSW Eco session on Monday, especially when you consider that at least a third of the food produced goes in the trash and that a quarter of our water usage goes to producing that food.

As the world’s population swells, "we hear a lot about how we’re going to have to ramp up food production to feed all these people, but in that conversation, we don’t often talk about food waste," said Philpott said.

Former Trader Joe’s president Doug Rauch talked about his new project, Daily Table, a grocery nonprofit set to open in Massachusetts this fall that will sell food that other grocery stores won’t. Not food that is unhealthy to eat, but the billions of pounds of food that grocery stores currently throw out because the "sell-by" or "best-by" date has passed.

"From the outside, it seems like there is a rational system about when we should or shouldn’t eat our food, but there are no federal guidelines and they are mostly arbitrary," said Dana Gunders, a scientist with the Natural Resources Defense Council. "It’s up to manufacturers if they are going to use a date, as well as what words they use and how they come up with that date."

Without labeling standards, confused customers often choose to play it safe and throw out food based on what’s printed on the label, even if it just says "best enjoyed by."

(The NRDC just published an entire report on this issue called The Dating Game, which you can find at nrdc.org/food/expiration-dates.asp.)

Part of the problem is the term "food waste." "Wouldn’t you like to eat some food waste?" Rauch asked the crowd, which responded with a laugh. "But if I said, ‘Would you like to eat some wholesome excess nutritional food?’ you’d go for it."

Advocates for food rescue also face the uphill challenge of persuading customers that the food, though not "good enough" for regular grocery stores, is not just safe, but respectable to eat. "This isn’t second rate or third rate product; it’s just about education," Rauch says.

Food waste becomes a hunger issue when you consider that that food, including perfectly edible but cosmetically blemished fruits and vegetables, are being thrown out in a country where the 50 million people aren’t sure where their next meal is coming from.

One of the panelists, Kavita Shukla, explained how she was inspired to start her company, Fenugreen, which makes sheet of paper that help prevent spoilage. Shukla recalled visiting her grandmother in India when she was young and, forgetting that she wasn’t supposed to drink the tap water, drank a whole glass of it after brushing her teeth.

Her grandmother mixed a bunch of spices and herbs together to make what she remembers as a "brown herb water," which kept her from getting sick. She spent her high school years investigating natural methods of preventing spoilage and, in 2011, launched the edible paper is infused with organic spices that keep fruit and vegetables fresh for two to four times longer than normal.

Consumers aren’t just the ones who are throwing the food away; they are the ones who, consciously or not, demand that grocery stores keep perishable food stocked on shelves night and day. Rauch explained Trader Joe’s "7:42" policy, which means the stores, especially the produce and meat sections, should be as full at 7:42 at night as first thing in the morning.

Many grocery stores donate fresh produce to local food banks, but some of them recover food from their own store and use it in prepared foods the next day. Rauch says that when you look at the big picture, only three percent of the food that’s wasted is wasted at the grocery store. The vast majority of it is wasted at home.

Gunders says that we need to implement the "reduce, reuse, recycle" logic to food.

"You’re hearing a lot about composting, but that isn’t the best and highest use for food," she said. "We need to start at reduce."

Gunders also pointed out that not all food waste is equal. Throwing out a pound of carrots and a pound of ground beef, for instance, leave very different environmental footprints, she says. "If you throw away a hamburger, it’s the same as a 90 minute shower," she said. (If that statistic sounds out of whack, check out this water calculator from National Geographic.)

It’s changing the little habits of everyday Americans that are both the easiest and hardest things to change. "Ultimately, this is a cultural problem," she says. "When you throw away food, just take a second to think about why you are throwing out the food in the first place."