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It's barbecue season around the SciShow office, which means applying our knowledge of science to this delicious outdoor past-time.

Hosted by: Stefan Chin

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Cutting across the grain



Low n’ slow

Resting meat
[ intro ].

It's summertime for those of us in the northern hemisphere, which means one thing: barbecue season. This style of food prep is a summer favorite because it's all about heat, flames, and how to control them for the tastiest meat or veggies.

And just like your kitchen at home, there's plenty of overlap between a chemistry lab and your backyard barbecue. So here are five science-based hacks that you can use at home to step up your barbecue game. First things first: whether it comes from a cow, pig, fish, or edible vertebrate of choice, that protein-rich slab of meat is muscle.

And land-based animals have layers of connective tissue wrapping those tiny muscle fibers into bundles. A type of connective tissue called perimysium wraps those bundles into larger bundles. This bundle-ception continues until it's no longer microscopic.

You can even see the bundles if you look closely. But the way that the connective tissue wraps around muscle fibers determines the grain of the meat, or which direction those bundles point towards. Now, some cuts of meat like skirt steak or flank have a thicker, more easily visible grain.

They have larger muscle bundles with lots of connective tissue compared to something like tenderloin. This makes them tougher to the bite, which is where this tip comes in handy. Cutting at a 90 degree angle to the grain, as opposed to parallel with the grain, will result in a more tender bite in your mouth.

How do we know? Well, tenderness is a hugely sought after quality, so folks in the meat industry actually measure this. But you can't just have a group of people taste testing burgers all day, so a procedure called the Warner-Bratzler Shear Force test was invented to objectively assess meat tenderness.

You basically take a tube-shaped section of meat and put it under a mini guillotine, then measure how much force it takes to cut through the sample. This test mimics what we do with our teeth when we bite into a steak, so it's a pretty good standard for objectively measuring tenderness. Now, back in your backyard, by cutting perpendicular to the grain, you're separating the muscle into a cross section: short muscle fibers separated by that structurally weak connective tissue.

A 1985 study in Meat Science -- which is a real, peer-reviewed journal -- showed that perimysium broke down much more readily than muscle fibers. So by cutting across the grain, you're letting the heavy butcher knife do the work of breaking down the muscle so your teeth don't have to. Most of the time, adding heat is a predictable experiment.

The longer you cook something for, the hotter it becomes until it burns to a crisp. But something different happens when you slow cook meat on a barbecue. It's a phenomenon known as the barbecue stall.

The internal temperature of the meat will climb for a while, but then level out -- even though it's still over hot coals. The internal temperature might stall for hours, leaving you to wonder if the gods of thermodynamics have somehow cursed your grill in particular. A few explanations have been offered.

Like, maybe the heat energy is selectively melting the fat. Another is that collagen, a protein in connective tissue, turns into liquid gelatin when temperatures get above 70 degrees Celsius. But stalling happens at an internal temperature around 60 to 70 degrees Celsius, too cool for collagen to gelatinize or for fat to melt.

So a more likely hypothesis is that this leveling out is due to evaporative cooling. Water inside the meat evaporates and carries heat away -- much like how sweat cools our skin on a hot day. Then once the meat dries out a bit, the internal temperature finally starts to rise again.

Now, researchers from Texas A&M University attempted to measure this a few years ago at a food-themed outreach event. They did their experiment in the most Texan way possible: they threw a cookout and measured the stall in real time. To do this, they compared the internal temperatures of brisket wrapped in foil to totally exposed meat, and they found that meat without foil experienced a stall at sixty degrees for about two hours, but the foil-wrapped meat didn't.

They concluded that the foil prevented the evaporative cooling effect, so the meat continued to rise in temperature. In two thousand eleven, a physicist performed an informal citizen science experiment where he took a chunk of beef fat and threw it in a smoker alongside a sponge filled with cellulose water. Fat is hydrophobic, meaning it doesn't store water like muscle does.

So it shouldn't experience any stall from water evaporating. Sure enough, the sponge experienced a temperature stall comparable to a proper brisket. On the other hand, the fat heated up steadily and ended up as a glistening puddle on the bottom of the smoker.

When you think of marinades, you probably think of the good old immersion technique. Soaking the meat in some kind of salty, flavorful, or acidic liquid for a long period of time can do everything from adding flavor to tenderizing before meat hits the grill. But it's more complicated than that.

Certain ingredients are better at certain jobs than others. Marinades like brine or soy sauce can be used as a tenderizer because of their high salt content. That's because salts are good at breaking down what are called myofibrillar proteins, namely actin and myosin.

In a living animal, these filaments slide past each other to perform muscle contraction, but when muscle becomes meat, they're still complex, interlocking structures. Luckily, the salts can unfold them. Specifically, the negative chloride ion in salt binds to the filaments and creates an electrostatic repulsion.

While the filaments are usually tightly packaged, this repulsion spreads them apart and lets water molecules trickle into the newly opened areas. It's like using similar poles of a magnet to repel each other, but instead of magnets, you have similarly charged ions. This increases the space between strands of protein, which lets the muscle hold on to even more water.

Now, sometimes you might choose acidic marinades like lime juice, lemon juice, or vinegar, which tenderize meat slightly differently. Marinades with a low pH do help break down some of that connective tissue and add flavor to the meat, but don't increase the meat's ability to hold onto water. One solution, according to a 2007 review in the journal Applied Poultry Research, was to combine the water-retaining properties from salty marinades with more acidic solutions to get the best of both worlds.

A final type of marinade involves using enzymes from fruits, like papain from papayas or bromelain from pineapples. These types of marinades tenderize meat by breaking down the connective tissue between muscle bundles. As for how long you should marinate for, that's up to you.

Researchers in 1999 found that chicken fillets experience their biggest uptake in water during the first five minutes of marination, with much slower absorption in the half hour afterwards. But a study published in 2010 compared the effect of marinating time on servings of chicken and found that the best tasting fillets resulted from a three hour soak time, compared to 30, 60, or a 120 minutes. So do you really need to marinate overnight?

Well, you can see some benefit in just a few minutes, but you might notice more flavor after a longer soak. Look, we've all been there. Figuring out the delicate balancing act of exactly how many seconds in the microwave makes the difference between a burrito that's frozen in the middle versus one that tastes like rubber.

And grill masters run into the same problem, just with really big slabs of meat. They want to end up with a brisket that's both tender and juicy, which is tricky. Meat needs to reach a certain temperature threshold for some of its tougher elements, like collagen, to break down.

But crank up the heat too high and you'll lose more water, making it taste dry. Enter slow cooking — using low temperatures applied over multiple hours of cooking time to get exactly the right internal temperature. And that precision is necessary because different chemical events happen at different temperatures.

By fifty degrees, you've already started denaturing some of the proteins in meat, like myosin. The tough connective collagen starts to denature and become gelatin between sixty and seventy degrees. But, you want to stick to the lower end of that range, because the enzyme that helps break down collagen is only active under sixty degrees.

And that process takes its sweet time. A 2005 review found that it took more than six hours to see significant tenderization benefits from slow cooking. So the sweet spot seems to be an internal temperature around sixty, definitely not higher than seventy degrees — that way, the proteins that are tough to the bite have denatured, which tenderizes the meat.

Meanwhile, it's lost as little moisture as possible. Even just a few degrees hotter and you risk losing the benefits. Although increased temperatures will further denature collagen and turn it to gelatin, the meat overall starts to shrink as water is lost.

That means the other proteins in the meat will start clumping together, making it tougher. Researchers in 1968 reported that as meat rose above sixty degrees Celsius, the tenderness progressively decreased. Basically, the extra breakdown of collagen can't compensate for the toughness caused by the other proteins condensing.

This is why slow cooking is desirable. There's little room for error when you're aiming for the best balance between juiciness and tenderness. You need to hit a super precise temperature target, and slow cooking makes that easier to do.

Other than keeping you from burning your mouth, allowing barbecued meat to rest for a few minutes after taking it off the grill will actually help it retain moisture. Usually that means taking meat off the grill and subjecting it to less intense heat before slicing into it. During cooking, some of the proteins, including actin, myosin, and collagen, shrink together, which decreases the amount of space available for water to hang out.

Think of any time you may have overcooked a chicken breast. It probably shriveled up and dried out. Now, at certain temperatures, the proteins shrink irreversibly.

Contrary to the popular belief behind this practice, these proteins don't get their structure back if they cool down. Once they're heated up, they stay in that misfolded shape. But other mechanisms can reabsorb some of the water that's been squeezed out.

It's been hypothesized that capillary action, the phenomenon where water moves through thin columns on its own, could play a role. On paper, the spaces between muscle filaments could pull up a column of water up to three hundred meters -- if you could find a slab of meat that big. But it hasn't been investigated specifically in reference to the resting effect.

But a lot of water stays outside of the filaments, so regardless of how long you rest the meat, you still can't hold on to all of it. Unfortunately there's no universal law for how long you should rest the meat, but as a general rule, the larger the roast, the longer you wait. So next time your friends laugh at you for claiming science can enhance your barbecue, show them the light with your flawless brisket.

All it takes is a little understanding of the chemistry of protein, fat, water, and salt. Thanks for watching this episode of SciShow. If you liked this one, you might like our podcast SciShow Tangents.

Each week we get together to astound each other with science facts -- with an ever so slight competitive twist. We even have an episode on the science of cooking. So check out SciShow Tangents wherever you get your podcasts. [ outro ].