Koji Prime Rib Recipe (2024)

Why It Works

  • Separating the roast from the rib bones prior to cooking allows for more even seasoning of the meat and easier carving at the end. Tying the roast back onto the bones for cooking helps insulate the meat, keeping it moist while promoting even cooking.
  • Slathering the roast with funky shio koji amplifies the beefy flavor of prime rib, imparting savory depth to the meat, while also tenderizing it. The sugars in the shio koji also help the prime rib achieve a well-browned crust.
  • Slow-roasting in a low oven cooks the prime rib evenly from edge to edge.

Prime rib is an iconic holiday centerpiece that doesn't need much gussying up; the beauty of a beef roast lies in its simplicity. Here at Serious Eats, Kenji has covered this cut exhaustively, making it so that nobody should feel intimidated by the prospect of cooking this very expensive piece of beef. But that doesn't mean there isn't room to give a rib roast a helping hand, so that it achieves its full flavor potential.

This year, we wanted to try something new with prime rib, to up the ante on its rich, beefy, savory flavor. So I turned to one of the best flavor amplifiers I know,shio koji, to make the ultimate holiday roast: koji prime rib.

Shio koji is a Japanese marinade, commonly used with poultry, meat, and seafood, that taps into the flavor potential ofAspergillus oryzae(akakoji-kinor just "koji" if you're already on a first-name basis), the mold that also gives us miso, soy sauce, and sake. Shio koji is made by fermenting a mixture of grain koji (cooked grain, most commonly rice, that has been inoculated with koji spores and then dried), salt, and water to create a porridge-textured product with a sweet, funky aroma.

Koji Prime Rib Recipe (1)

This koji prime rib is the most savory, meaty, juicy, and delicious beef roast that I've ever cooked. And it's so easy to make. So if you're looking to get wild this holiday season, do yourself a favor—stop reading this, and go start a batch of funky, salty-sweetshio kojiright now (if you don't have some in the works already).

The Ins and Outs of Koji Prime Rib

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The process for making koji prime rib is almost identical to the oven reverse-sear method that Kenji uses in hisprimer for perfect prime rib. While we don't need to rehash each step in minute detail, it's worth going over the basics, as my iteration has a few little tweaks and innovations of its own.

Take Roast Apart, Slather It With Shio Koji, Tie It Back Together

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First and foremost, a roast needs to be seasoned before cooking. I recently wrote a guide to our favorite method for seasoning both large and small cuts of beef, thedry brine. The TLDR version of that article is "season the meat with salt, let it rest, cook it." For large roasts like pork shoulder and prime rib, you'll achieve the best results by seasoning a day ahead of cooking, then allowing the roast to rest, uncovered in the fridge, overnight. Dry-brining produces well-seasoned meat that browns beautifully while holding onto its juices.

For this recipe, I took the same principles of dry-brining and replaced the salt with shio koji. Shio koji is plenty salty ("shio" is Japanese for "salt" after all), but as with other koji-derived ingredients like soy sauce and miso, it doesn't just provide salinity; it lends savory depth to foods that it comes into contact with, thanks to protease enzymes that break down proteins into amino acids, which we perceive as umami. This enzymatic activity not only boosts flavor but also has a textural effect on ingredients, making meat and poultry incredibly juicy and tender.

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In order to maximize the effect of shio koji on the prime rib, I start by separating the roast from the rib bones, which increases the surface area on which to rub the shio koji by exposing the interface between the meat and bones. Along with providing more even seasoning, cutting the roast off the bone and tying the two pieces back together before cooking makes carving much easier later.

AsKenji notes in his guide to prime rib, "The best way to cook your beef is to detach the bone and tie it back on. You get the same cooking quality of a completely intact roast, with the advantage that once it's cooked, carving is as simple as cutting the string, removing the bones, and slicing." Why keep the bones at all? Because they help insulate the meat, promote even cooking, and are also delicious to gnaw on at the table!

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So slather up a prime rib with shio koji (you can blend shio koji until smooth if you'd like, but it's not necessary for this application, as it will still adhere to the meat just fine in its porridge-like state), before tying it back to its rib bones with butcher's twine.

Overnight Rest

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With the seasoning and trussing taken care of, it's time to let the roast rest, uncovered, on a wire rack–lined sheet tray in the fridge overnight. This gives enough time for the shio koji to do its thing. When you pull it out the next day, you'll notice how dry the surface of the roast has become—this, along with the sugars in the shio koji, will make for a deeply browned crust at the end of the roasting process.

Before popping the prime rib in the oven, I use a paper towel to lightly brush any excess bits of rice from the surface of the meat. There's no need to obsess over it by removing every last grain; just get any that stick out. Those pieces can easily burn when the prime rib gets its high heat blast at the end, and we don't want that. (This isn't an issue if you blend the mixture first, which is one small argument in favor of doing it.)

Slow-Roast for Even Cooking

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The roasting process follows our standard low-and-slow reverse-sear method. Cooking the roast at a low temperature allows us to achieve beautifulrosy meat from edge to edge.

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Depending on how low a temperature your oven can go, along with how well-done you like your prime rib cooked (I'm with Daniel, who favors prime rib cooked closer to medium than mid-rare; with so much interior real estate in a prime rib, I don't love chewing on thick bites of medium-rare beef with no crust to break up the textural monotony), the roast will take four to five hours to cook.

Blast It for a Browned, Crispy Crust

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Get the roast out of the oven and make a little foil fort for it while it rests. While it hangs out, turn the heat all the way up on your oven to give it a final blast for crispy, crusty, koji perfection. As I mentioned earlier, the sugars in the shio koji will accelerate browning, so keep an eye on the roast once it goes in the oven for this final step.

Koji Prime Rib Recipe (10)

Also, once the roast comes out of the oven and moves to your carving board, don't forget to save the jelly-like beef juices that will have dripped down onto the foil-lined baking sheet. That's the good stuff! Spread it on bread, eat it with a spoon, fold it into a sauce. Just don't let it go to waste.

Untie and Slice

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Having already separated the meat off the rib bones before roasting, carving is a breeze. Just snip away the butcher's twine to release the roast from the bones once more.

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Cut between the bones to separate them into gnawable individual pieces, and start slicing up that juicy beef. Whatever you do, promise me you won't throw out any delicious (and expensive) prime rib fat, even if you're not planning on serving or eating all of it. I'll show you what to do with it in just a moment.

Koji Prime Rib Recipe (13)

But first, let's take a moment to appreciate the finished koji prime rib. It's beautiful to look at, sure, but just wait until you take that first bite. It's hard to describe what the flavor is, if not simply "extra." The koji amplifies the already pronounced beefy flavor of prime rib, while also lending a very subtle sweetness to the meat.

Koji Prime Rib Recipe (14)

It's intensely savory, and impossible to stop snacking on. When I cooked the roast for these photos in the Serious Eats test kitchen, there were at least five people milling around, waiting for their time to pounce and snack, who then found they couldn't tear themselves away. Between mouthfuls, Daniel kept reminding himself out loud how he usually isn't a big fan of prime rib. And then he would grab another bite. This prime rib is different, in the best way.

And if you’re already going over the top with this prime rib, why not accompany it with an equally luxe shio koji-spiked jus?

Render and Save Your Beef Fat

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If you've bought a prime rib roast before, you're well aware that they don't come cheap. So if you are tempted to throw out any scraps of meat and fat that crop up when cutting the loin off the ribs, or any of the fat from the finished roast, then understand that you are throwing money—and flavor—away. (This applies to all food waste of course.)

That fat is delicious, especially if you sprung for a dry-aged piece of beef. It's your duty to put it to good use! The simplest way to process any scraps of fat is to render them in a saucepan with woodsy aromatics like rosemary and thyme. That rendered fat is gold. Strain it and keep it in the fridge, deploying it whenever you want to give a meaty boost to cooking projects.

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In recent weeks, I've been using my rendered dry-aged beef fat for simple pleasures like dipping crusty bread but also for cooking. The past two dinner parties I've hosted at home have featured a dish of young carrots roasted in dry-aged beef fat with an herby tahini sauce. They're pretty phenomenal, and I've gotten a couple of messages from friends asking for the recipe. I plan to write it up soon, but for now this koji rib roast will have to tide them over.

Koji Prime Rib Recipe (17)

December 2019

Recipe Details

Koji Prime Rib

Active15 mins

Total17 hrs

Serves6to 12 servings

Ingredients

  • 1 standing rib roast (prime rib), 7 to 12 pounds (3.2 to 5.4kg; see notes)

  • 1 cup (300g; 240ml) shio koji (see notes)

  • Freshly ground black pepper

For Serving:

  • Koji beef jus (optional)

Directions

  1. For the Prime Rib (the day before roasting): Using a sharp knife, cut meat away from bone in one piece, cutting as close to the bone as possible, leaving you with a boneless roast and a slab of rib bones; reserve rib bones. Pat roast dry with paper towels; then using your hands, slather shio koji over entire surface of the roast and rib bones. Place roast back on bones, and, using butcher's twine, tie together so that roast looks as it did before meat was removed from the bones. Transfer roast, fat cap side up, to a wire rack set in a foil-lined rimmed baking sheet, then refrigerate, uncovered, at least 12 hours and up to 24 hours.

    Koji Prime Rib Recipe (18)

  2. When Ready to Cook: Adjust oven rack to center position and preheat oven to 225°F (110°C). Using a paper towel, gently wipe away excess bits of shio koji from the fat cap side of the roast. Transfer baking sheet with rack and roast to oven and cook until internal temperature registers 125°F (52°C) on an instant-read thermometer at the roast's thickest point for medium-rare or 135°F (57°C) for medium, 4 to 5 hours.

    Koji Prime Rib Recipe (19)

  3. Remove roast from oven, tent loosely with foil, and let rest at room temperature for at least 30 minutes and up to 1 1/2 hours. Meanwhile, increase oven temperature to 500°F (260°C) or highest possible temperature.

  4. Ten minutes before guests are ready to be served, remove foil, place roast back in hot oven, and cook until deeply browned and crisp on the exterior, 6 to 10 minutes. Remove from oven, and transfer roast to a carving board.

    Koji Prime Rib Recipe (20)

  5. For Serving: Cut away twine, and separate roast from ribs. Using a sharp knife, cut between ribs to separate into individual pieces, and then slice roast into 3/4-inch-thick slices. Serve right away, passing coarse sea salt and koji beef jus (if using) at the table.

    Koji Prime Rib Recipe (21)

Special Equipment

Butcher's twine, rimmed baking sheet, wire rack, instant-read thermometer

Notes

This recipe works for prime rib roasts of any size, from three to six ribs. For best results, use a dry-aged prime-grade or grass-fed roast. Cooking time is identical regardless of the number of ribs on the roast.

We do not recommend using store-bought prepared shio koji for any recipe, as store-bought versions vary wildly in quality. They are often too sweet and are treated with alcohol to extend shelf life. Making your own shio koji is worth the effort.

This recipe is best enjoyed right away.

Read More

  • Koji Beef Jus
  • The Food Lab's Definitive Guide to Prime Rib
  • Roasted and Reverse Seared Prime Rib
  • Perfect Prime Rib With Red Wine Jus
Koji Prime Rib Recipe (2024)

FAQs

What makes prime rib so delicious? ›

Prime rib has a large “eye” of meat in the center, which is juicy, tender, and marbled with fat. This eye has a fat-marbled muscle around it, and the whole thing is surrounded by a thick cap of fat. This means that prime rib is tender, juicy, and extremely flavorful because the muscles aren't heavily used.

Is butter or olive oil better for prime rib? ›

If you are searing a roast with butter before or after cooking it, it is more likely to burn due to its low smoke point. Instead, David Rose recommends home cooks use olive oil or grapeseed oil to lessen any chance of the roast charring.

How to use beef tallow on prime rib? ›

Create the mixture: In a medium bowl, combine the beef tallow (use mayo if you can't find tallow), herbs, salt, pepper and garlic. Using a spatula, evenly coat the prime rib with the mixture.

How do restaurants make prime rib so tender? ›

How do restaurants make prime rib so tender? The secret to restaurant-style prime rib is cooking the meat super slow at low temperatures. I recommend cooking prime rib at no higher than 200 degrees F. This cooks the meat very slowly, turning the fat into butter and rendering the proteins juicy and soft.

What is the most important thing to do before roasting a prime rib roast? ›

Rule #7: Season Well, and Season in Advance. For best results, salt your prime rib on all surfaces with kosher salt at least 45 minutes before you start cooking it, and preferably the day before, leaving it in the fridge uncovered overnight. Initially, the salt will draw out some moisture and end up dissolving in it.

Is prime rib better cooked slow or fast? ›

Cooked low and slow in the oven and finished with a blast of heat for the juiciest, most flavorful, evenly cooked prime rib roast. Kenji is the former culinary director for Serious Eats and a current culinary consultant for the site.

Why is my prime rib always tough? ›

Overcooking the Prime Rib

That's why prime rib is so expensive: it's a huge piece of extremely good beef. Therefore, it's important not to cook it beyond medium-rare. Going past that temperature means the roast will no longer be tender.

Why do you salt prime rib before cooking? ›

The salt helps trap the heat to better cook the prime rib. “It conducts the heat and seals it,” says Betz.

Is it better to cook prime rib at 325 or 350? ›

Start by cooking your prime rib at 500°F for 15 minutes and then lower the oven temperature to 325° F and cook for 10-12 min per pound for rare, or 13-14 min per pound for medium rare, or 14-15 min per pound for medium well. A meat thermometer is essential to ensure you cook it perfectly!

Is it better to sear prime rib first or last? ›

Searing is an important part of roasting a prime rib. Searing the roast first will kill the surface bacteria, which is a nice touch, especially when you are roasting at lower temperatures.

Do you cook prime rib fat side up or down? ›

Place the roast fat side up, bone side down, in a large roasting pan. Cook for 15 minutes, then reduce the oven temperature to 325°F. This allows the heat to sear the roast, trapping the juicy flavors inside while the rest of the meat cooks. On average, each pound of rib needs 15 minutes to cook (i.e., a 4 lb.

How to add flavor to prime rib? ›

Place the prime rib on a roasting rack and set in a roasting pan on your grill. I always add a little water to my pan and wow does it give you some amazing flavor! Use fresh herbs. I love using fresh thyme, sage, oregano and parsley.

What to inject prime rib with? ›

Injection mixture. I combined soy sauce, Worcestershire sauce, au jus base, beef broth, and Heath Riles BBQ Everyday Rub to make the injection for this prime rib roast. Red wine. Wine gives any dish an elevated flavor profile and will be a key ingredient when I make the au jus.

Should you trim fat off prime rib before smoking? ›

Trim the prime rib roast of any unwanted fat. It's important to leave some fat still, as that will help flavor the meat. Truss the prime rib using butcher's twine. Coat the roast on all sides with olive oil.

What is the 500 rule for prime rib? ›

The Secret To Making Perfect Prime Rib: The Cooking Method

Preheat your oven to 500 degrees (F), or as high as it will go without activating the broiler function. Carefully place the prime rib roast into the preheated oven, uncovered, and cook for 5-6 minutes per pound.

What is the best temperature to cook a prime rib roast? ›

Brown the roast at 500°F (or as high as your oven will go) for 15 minutes. Lower the oven to 325°F to finish roasting: Reduce the oven temperature to 325°F. Roast in the oven until the thermometer registers 115°F for rare or 120° for medium rare, and 130°F for medium.

What is the best way to get prime rib cooked? ›

Cook the prime rib at 500 F for 20 minutes. Then, turn the heat down to 325 F and cook it for another 1.5 hours – or until the internal temperature reaches. Once it's done, allow it to cool for 40 minutes under a foil tent. Then, slice it, serve with your favorite mashed potatoes, and enjoy!

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