You are what you eat. Your mom told you that. Turns out it’s true for farm animals, too. When animals live on pasture, they eat a more varied diet of different grasses, herbs, and flowers. The diet has an enormous impact on the flavor of meat it produces.

Perhaps the most famous example is Ibérico de Bellota pork. Black Ibérico hogs root and roam in the oak forests of southern Spain. All year, they chow down on the roots and twigs and grubs on the forest floor. In the autumn, when acorns (“bellotas” in Spanish) fall, they gobble them up like crazy. A pig will eat as much as twenty pounds of acorns a day. Ibérico pork is always delicious, but the nut-heavy diet has an incredible effect on the meat: the flavor is deep, rich, earthy, intensely savory. And the texture is luscious. The fat practically melts into a silky, savory puddle on your tongue. Nearly all of the Ibérico de bellota pork you find on the market is cured—ham is what you’ll find most often. But once in a blue moon you may find fresh Ibérico de bellota. Either way, it’s an exceptional eating experience.

The Spanish used to be the only ones taking advantage of the acorn secret. But for a few years now, Iowa’s premiere pork palace, La Quercia, has been curing hams made from heritage Tamworth-breed pigs raised in Missouri that finish their lives out in the forest eating an acorn-heavy diet. These American acorn edition hams rival any that are coming out of Europe.

Of course, acorns aren’t the only food that give flavor to meat.

Just the opposite. Everything that is fed to an animal impacts its flavor. So, when the meat industry took chickens and pigs and packed them into enormous barns and started feeding them a standardized diet of corn and soy and antibiotics, that bland, homogenized feed had its impact on the flavor of the meat. It dumbed it down, flattening the rainbow of flavors to a monotone. The same of true of beef: whether the animal finished its life eating grass on the range or corn in a feedlot makes a huge difference in the flavor.

All beef cattle start their lives eating grass.

For the first seven or eight months of its life, a calf will live out on pasture with its mother, drinking milk and eating grass. It’s what happens next that determines whether a cow is “grass fed” or not. Grass fed cattle will spend their entire lives out on pasture eating grass. That accounts for only a tiny percentage of the cattle out there. Nearly all of them are trucked to crowded feedlots. At the feedlot they’ll spend another half a year or so fattening up. In the best case, like with organic beef (which is usually feedlot finished), they’ll be given their fill of certified organic grains like corn and soy. However, the norm for most feedlots is to dole out a diet of corn, growth hormones, antibiotics, and whatever agricultural byproducts the Big Agriculture industry can get away with, like chicken poop (really). But don’t worry, you can rest easy because at least the FDA has put bans on feeding cattle the really bad stuff, like byproducts of other cattle. (Until 1997, feedlot cattle were routinely fed things like blood meal, a high-protein powder made of dried animal—including cow—blood. Then somebody figured out that feeding cow byproducts to cows was a primo way to spread Mad Cow Disease. Incidentally, there’s no rule against feeding cow byproducts to chickens. When cows are then fed chicken poop, they may still indirectly be eating cow leftovers.)

A hundred years ago, no one would have dreamed of feeding grain to cattle. If left to themselves they don’t touch the stuff; cattle don’t graze in corn fields. Besides, grass grew in abundance and it was free for the grazing. But around the middle of the 20th century, a few factors conspired to make grain finishing an enticing option. One was the new subsidies from the federal government given to grow corn, which inspired a glut of corn on the market and drove down prices, making it economical to compete with “free” grass. Another was the increasing demand from new fast food restaurants for a steady, year-round supply of beef.

Grass fed beef is as seasonal as a summer tomato.

A century ago, fresh beef was a seasonal product. With a regulated diet of corn, the cows receive the same nutrition all year round, making the quality of the beef more uniform all year round. But when cows eat grass the quality of the beef is dependent upon the quality of the grass. During the winter or the dry season when the grass isn’t doing so well, the cows don’t do so well, either. When grass-fed cows are brought to market while the grass has little nutritional value, the beef is much tougher and chewier. One key to finding consistently good grass fed beef is finding a rancher who will only take their cattle to slaughter when the grass is in season. That’s exactly what Bill Niman of BN Ranch in California and Cory Carman of Carman Ranch in Oregon do. Between about December and May when the grasses aren’t great, they don’t produce any fresh beef. When they do produce beef in the summer, it is hugely flavorful.

Knowing that a cow was grain or grass fed isn’t by itself enough to know that the beef will taste better. In either scenario, the beef can end up being mediocre or very, very good. It depends on the work done by the rancher to manage the cattle. That said, grain fed beef is likely to be more consistent all year round, because the farmer can decide exactly what to feed the cattle any day of the year. It tends to be a bit sweeter, and it has a richness from all of the fat that the animal puts on. Sometimes that fat can be enough to feel like it coats the inside of your mouth. Grass fed beef will vary more across the year depending on the quality of the grass. When a rancher manages their pastures carefully and only sends their cattle to market when the grass (and thus the cow) is in peak condition, the beef is tender and juicy, and the flavor tends to be a little earthier and more mineral, with a huge, robust beefiness. That flavor will vary a bit depending on the season: spring beef tends to be a bit lighter, while autumn beef will be a bit more rich. The more diverse the grasses, the more complex the flavor.