Kimchi Smash Burger en Madrid: la única con kimchi fermentado en casa | STILLROOM Jerónimos

Kimchi Smash Burger in Madrid: STILLROOM's unique offering

Located in the heart of the Los Jerónimos neighborhood, just a two-minute walk from the Prado Museum, STILLROOM has established itself as one of Madrid’s most innovative gastrococktail bars. The venue, located at 9 Moreto Street, combines a signature cocktail menu with a culinary offering that isn’t afraid to experiment with flavors from around the world.

La Kimchi Smash Burger representa la apuesta más audaz del equipo de cocina por fusionar la tradición coreana con la técnica estadounidense del smash burger. Lo que hace a esta burger verdaderamente única en el panorama gastronómico madrileño es su kimchi fermentado en casa durante 24 a 48 horas, un proceso que ningún otro establecimiento de la capital replica con este nivel de dedicación.

The smash burger craze has taken Madrid by storm in recent years, with dozens of restaurants offering their own take on the burger pressed flat on a hot griddle. However, STILLROOM has set itself apart by incorporating artisanal kimchi, elevating what might seem like a casual dish to the level of a sophisticated dining experience. The homemade fermentation of the kimchi adds a complexity of acidity and umami that no industrial product can replicate, turning every bite into a sensory journey between Seoul and Texas.

Anatomy of a Bite: Layer by Layer

STILLROOM’s Kimchi Smash Burger is a meticulously crafted dish in which each element plays a specific role in the dish’s overall balance:

• Brioche bread: soft, slightly sweet, with a golden crust that provides structure without being heavy.
• First layer of smash beef (80g): high-quality beef pressed at high temperature to create a rich, caramelized crust.
• Melted American cheese: It melts over the hot meat, adding creaminess and a distinctive salty flavor.
• Second layer of smash steak (80g): a second medallion that doubles the meaty flavor and creates layers of crispy texture.
• Homemade fermented kimchi: the star of the show, with its crunchy texture and tangy, spicy, and deeply umami flavor profile.
• Caramelized onions in beef fat: slowly cooked in the fat rendered from the beef, adding sweetness and depth.
• House-made hot sauce: a touch of heat that enhances the dish without overpowering the other flavors.
• Bread base: serves as a stable platform to hold all the above elements.

This layered structure is no accident: the contrast between the creaminess of the cheese, the tanginess of the kimchi, the sweetness of the onion, and the crispiness of the crust creates a multidimensional experience in which no single flavor overpowers the others. Each layer contributes texture, temperature, and flavor in a balance that only works when all the elements are present.

Why Make Homemade Fermented Kimchi: The Technique

Lactic fermentation is the process that transforms raw napa cabbage into the distinctive kimchi we know. This traditional Korean method harnesses the lactic acid bacteria naturally present in the vegetables to turn them into a living food, rich in probiotics and with a flavor profile that evolves over time.

STILLROOM’s kimchi is made using a rigorous process that begins with the selection of fresh napa cabbage, which is salted in a 3% brine to draw out excess water and create the right environment for fermentation. The cabbage is then mixed with gochugaru (Korean chili powder), fresh grated ginger, crushed garlic, and daikon strips. Some versions include Korean fish sauce to add umami depth, though this decision is left to the chef’s discretion depending on the season.

The fermentation process takes place in two stages: first, at room temperature for 24 to 48 hours, during which bacterial activity is most intense and the kimchi develops its most complex and slightly effervescent flavors; subsequently, it is transferred to the refrigerator for a slow fermentation that can last several weeks, losing intensity but gaining complexity.

The result is a kimchi with a complex acidity, a spiciness that warms rather than burns, and a deep umami flavor that acts as a natural flavor enhancer for the meat. An industrial, pasteurized, and preserved product could never offer this aromatic depth. That’s why STILLROOM makes its kimchi in small batches, ensuring that every burger served contains a living product at its peak of freshness. If you’d like to learn more about similar fermentation techniques applied to mixology, check out our cocktail and mixology glossary.

The Smash Technique: The Science of the Maillard Reaction at 280 Degrees

The smash burger owes its distinctive texture to the Maillard reaction, a chemical process that occurs when amino acids and reducing sugars interact at temperatures above 140 degrees Celsius. At STILLROOM, the griddle reaches exactly 280 degrees Celsius, a temperature that maximizes this reaction and creates the golden, crispy crust that defines a well-executed smash burger.

The technique involves placing a ball of ground beef (in this case, two 80-gram portions for the double version) on the hot griddle and immediately flattening it with a metal spatula. This flattening serves a dual purpose: on the one hand, it increases the surface area in contact with the heat, creating more space for the Maillard reaction; on the other hand, it forces some of the internal fat toward the surface, where it contributes to the formation of the crust.

The cooking time is short but precise: about 90 seconds per side. This is enough time to achieve the characteristic golden brown color without the meat losing its juiciness on the inside. The contrast between the crispy exterior and the juicy interior is what sets a smash burger apart from a traditional, thicker burger, where heat penetrates more slowly and can result in a drier texture.

The griddle temperature is critical: below 250 degrees, the Maillard reaction doesn’t occur with the necessary intensity, and the meat remains pale and lacking in flavor. Above 300 degrees, the outside burns before the inside reaches the proper temperature. STILLROOM’s 280 degrees represents the sweet spot where science and gastronomy meet.

How to make it at home: an easy version

Although recreating STILLROOM’s Kimchi Smash Burger at home requires some advance planning—especially because of the kimchi fermentation process—the result can be remarkably satisfying. Here’s a guide for making two servings:

• 400 grams of high-quality ground beef (at least 20% fat)
• 2 brioche burger buns
• 2 slices of American cheese
• 200 grams of napa cabbage for homemade kimchi
• 2 tablespoons of gochugaru
• 1 piece of fresh ginger (about 3 centimeters)
• 4 cloves of garlic
• 1 small daikon
• 3% brine (30 grams of salt per liter of water)
• 1 medium onion
• Hot sauce to taste
• Salt and ground black pepper

This process requires two days of preparation for the kimchi. First, cut the napa cabbage into manageable pieces and soak them in brine for 2–3 hours. Drain well and mix with the gochugaru, grated ginger, minced garlic, and julienned daikon. Pack the mixture into a glass jar, making sure it’s tightly packed, and let it ferment at room temperature for 24–48 hours. Then, store in the refrigerator.

For the burger, divide the meat into two 200-gram portions and shape them into loose patties. Heat a skillet or griddle to very high heat (aim for 280 degrees if your equipment allows). Place each patty on the pan and immediately flatten it with a spatula. Cook for 90 seconds per side, add the cheese during the last 30 seconds, and let it melt using the residual heat.

Assemble the burger with toasted brioche buns, drained kimchi, onions caramelized in the meat juices, and hot sauce. The result will come close to the STILLROOM experience, although professional technique and high-quality ingredients remain irreplaceable.

Where to try our Kimchi Smash Burger in Madrid

STILLROOM is located at Calle Moreto 9, 28014 Madrid, in the heart of the Los Jerónimos neighborhood, just a two-minute walk from the main entrance of the Prado Museum. Its prime location makes it the perfect spot for dinner before or after a cultural outing, or simply to discover one of the most innovative dining experiences in downtown Madrid.

El local abre miércoles y jueves de 18:30 a 01:30, los viernes y sábados desde las 11:00 hasta la 01:30 y los domingos de 11:00 a 23:00, ofreciendo la posibilidad de disfrutar de la Kimchi Smash Burger en un contexto de noche madrileña. Los lunes permanece cerrado.

To ensure availability, especially on weekends when demand is higher, STILLROOM recommends making a reservation through its online system at stillroom.co/reservar/. You can also call 619-21-36-16 for inquiries or large groups.

Nuestra recomendación de maridaje para acompañar la Kimchi Smash Burger es el cóctel Highball Martini Tomate, cuyo perfil umami complementa perfectamente los sabores complejos de la burger. Alternativamente, el cóctel Punch con mezcal y humo aporta un contraste ahumado que equilibra la acidez del kimchi. Ambos cócteles forman parte de una carta de 17 creaciones de autor que utilizan técnicas avanzadas como fat washing y lactofermentación.

Whether you're a smash burger lover looking for new experiences or a foodie eager to discover unexpected flavors, STILLROOM welcomes you to Los Jerónimos for an experience that combines technique, tradition, and creativity. Reserve your table and discover why the Kimchi Smash Burger has become one of the most talked-about burgers in Madrid.

Frequently Asked Questions About the Kimchi Smash Burger

What makes STILLROOM's Kimchi Smash Burger unique compared to other smash burgers in Madrid?

The main distinguishing feature is the kimchi, fermented in-house for 24 to 48 hours—a process that no other establishment in Madrid replicates with this level of dedication. While most smash burger joints use industrial sauces or store-bought kimchi, STILLROOM crafts its own from scratch, delivering a complexity of acidity and umami that is impossible to replicate. The combination of an 80-gram double smash patty, melted American cheese, and onions caramelized in beef fat completes a dish that has no equal in the capital.

Is the kimchi in the burger spicy? Is it suitable for all tastes?

STILLROOM's kimchi has a moderate level of spiciness, designed to complement the other flavors without overpowering the dish. The gochugaru adds a warmth that tingles the palate without being overpowering, perfectly balanced by the creaminess of the cheese and the sweetness of the caramelized onions. For diners who prefer to avoid any heat, you can request the burger without the spicy sauce, though the kimchi will always retain its distinctive character. If you have specific dietary restrictions, the kitchen team can advise you on available options.

Do I need to make a reservation to order the Kimchi Smash Burger?

Although it’s not required, we strongly recommend making a reservation, especially on Fridays and Saturdays, when demand for tables is significantly higher. The Kimchi Smash Burger is one of the most popular items on the menu and may sell out on busy nights. Booking through stillroom.co/reservar/ guarantees availability and avoids unnecessary waiting. For groups of more than four people, we recommend booking at least 24 hours in advance.

Which cocktail on the menu pairs best with the Kimchi Smash Burger?

Nuestra recomendación principal es el Highball Martini Tomate, cuyo perfil umami derivado de la reducción de tomate complementa perfectamente la complejidad del kimchi fermentado y la carne smash. Las notas ácidas del cóctel equilibran la grasa del queso americano mientras que el burbujeo del highball limpia el paladar entre bocados. Como alternativa, el cóctel Punch con mezcal y humo ofrece un contraste más intenso: el ahumado del mezcal interplaya con la acidez del kimchi creando una experiencia memorable para paladares aventureros.

Does STILLROOM offer vegetarian or kimchi-free options?

Sí, STILLROOM ofrece varias opciones para comensales que buscan alternativas vegetarianas o desean evitar el kimchi. El Hummus Stillroom es una opción ligera y cremosa elaborada con garbanzos caseros y especias. La Coliflor Asada con tahini ofrece textura y sabor ahumado muy satisfactorio. Para algo más ligero, el Edamame Salteado proporciona una opción saludable y sabrosa. Finalmente, la Burrata RAF con tomate y albahaca representa una elección clásica pero impeccable. Todas estas opciones están disponibles en la carta de cocina y maridan excelentemente con los cócteles de autor de STILLROOM.