Each year, about 40 percent of all food in the United States goes uneaten. It's just tossed out or left to rot. And that's a fairly large waste of resources. All that freshwater and land, all that fertilizer and energy — for nothing. By one recent estimate, Americans are squandering the equivalent of $165 billion each year by rubbishing so much food.

Nice tomatoes. Too bad 40 percent will get rubbished. (Tim Carman/Washington Post)

But these statistics don't tell the full story. How does the food actually get wasted? For that, here's a new report from the Natural Resources Defense Council that tries to track food waste up and down the system, from "farm to fork." My colleague Dina ElBoghdady has already highlighted some of the report's conclusions — including the fact that Europe does a better job of curtailing waste than the United States. But it's worth looking at where food actually gets wasted each step of the way. So let's follow the steps:

1) Farming: Roughly 7 percent of the produce that's grown in the United States simply gets stranded on fields each year. Some growers plant more crops than there's demand for, to hedge against disease and weather. Some produce goes unpicked because it doesn't meet standards for shape and color. At times, perfectly fine crops go unharvested after food-safety scares, such as the FDA's salmonella warning in 2008. Fluctuating immigration laws in states like Georgia can also create shortages of farmworkers, which can leave food unpicked.

2) Post-harvest and packing: After crops have been gathered from the fields, farmers tend to cull produce to make sure it meets minimum standards for size, color, and weight. "One large cucumber farmer," the NRDC report notes, "estimated that fewer than half the vegetables he grows actually leave his farm and that 75 percent of the cucumbers culled before sale are edible." If there's a culprit here, it's our high aesthetic standards for food.

3) Processing and distribution: Plenty of food gets trimmed in the manufacturing stage, though much of it is inedible anyway. Still, there's also a fair bit of avoidable waste. Technical malfunctions in processing and refrigeration are one big factor. Food can sometimes sit too long at improper temperatures and spoil. Another issue is that stores often reject shipments — and it's often difficult for distributors to find a new taker. After all, it's not as if food banks can always find a home for a truckload of rejected beets.

4) Retail and grocery stores: Grocery stores are another huge source of rubbished food — with the USDA estimating that supermarkets toss out $15 billion worth of unsold fruits and vegetables alone each year. But waste is also seen as the cost of doing business. Stores would rather overstock their shelves and throw out the remainder than look empty. Supermarkets will also winnow out produce that's in subpar condition, since few shoppers want to buy an apple that's all bruised up.

There's also the issue of "sell by" expiration dates. The report cites one industry estimate that each store throws out, on average, $2,300 worth of food each day because the products have neared their expiration date. Yet most of this food is still edible. In many states, it's still perfectly legal to sell food past its expiration date. Many stores would just prefer not to — it looks bad. "Most stores, in fact, pull items 2 to 3 days before the sell-by date," the NRDC report observes.

(The Washington Post/Source: National Resource Defense Council, Journal of Consumer Affairs, Food and Agriculture Organization)

5) Food service and restaurants: In restaurants, a good chunk of food is lost in the kitchen. And, on average, diners leave about 17 percent of their food uneaten. The report notes that portion sizes are a big reason for this, as portions have ballooned in the past 30 years. Restaurants also try to keep more food than they need on hand to make sure that everything on the menu is available. What's more, chain restaurants have inflexible rules that require perfectly good food to be tossed. McDonald's, for instance, requires fries to be thrown out after seven minutes. About one-tenth of fast food gets junked this way.

6) Households: This appears to be the big one. According to various estimates, American families throw out between 14 and 25 percent of the food and beverages they buy. This can cost the average family between $1,365 to $2,275 annually. A big factor here, the NRDC report notes, is that food has become so cheap and readily available. So, most people reason, what's the big deal if some of it gets tossed? The report also notes there's a great deal of confusion around expiration labels, which tend to be confusing and often prompt people to throw out food prematurely. (The British government has recently moved to revise these standards to make them less perplexing.)

7) Disposal: Not all discarded food is equal. The report estimates that only 3 percent of thrown-out food in the United States is composted. Most end up in landfills, where they decompose and release methane, a powerful heat-trapping greenhouse gas. In fact, about 23 percent of U.S. methane emissions comes from landfill food. Composting or even technologies to capture methane could reduce that.

The NRDC report argues that it is feasible to limit this food waste, if people were inclined (although it's not clear how big a reduction is possible). Granted, some waste is inevitable. If shoppers don't want to buy dented avocados or funny-looking carrots, there's not much a grocery store can do.

Still, the report notes that Americans today waste 50 percent more food than they did in the 1970s, which suggests that there's a fair bit of room to improve. What's more, Britain has managed to reduce the amount of household food tossed out by 18 percent over the past five years through a combination of public-awareness campaigns and resolutions by leading retailers to eliminate their downstream waste.