Cut the steak into 16 equal pieces if using a thin cut and 8 equal pieces if using a thick cut.
Season with ½ teaspoon salt and ½ teaspoon pepper.
Place the steak and mushrooms in a large bowl.
Add the olive oil, vinegar, rosemary, and garlic, and stir until the steak and mushrooms are well coated.
Cover with plastic wrap and refrigerate at least 30 minutes to 2 hours.
Place the potatoes in a large saucepan and add enough water to cover by 1 inch.
Bring the water to a boil and cook potatoes until just barely fork-tender, about 5-7 minutes.
Drain and set aside.
Add a piece of steak, a potato, another piece of steak, and a mushroom to a skewer.
Then add another piece of steak, a potato, another piece of steak, and a mushroom again.
Repeat with remaining 3 skewers and ingredients.
Heat a grill to medium-high and lightly oil the grate.
Add the kabobs and grill about 5-6 minutes on both sides, flipping every 3 minutes.
Sprinkle kabobs with remaining 1 teaspoon of salt and serve immediately.
Balancing Cook Times on a Single Skewer
Traditional beef kebobs often fail because dense vegetables require much longer exposure to heat than tender cuts of meat. Parboiling potatoes for precisely five to seven minutes ensures they reach fork-tender texture before hitting the grates. Threading ingredients uniformly prevents uneven zones where beef overcooks while starches remain firm.
Acid Interaction in the Marinade
Balsamic vinegar provides acetic acid that breaks down surface proteins on the ribeye, tenderizing the exterior during the thirty-minute rest. Olive oil carries fat-soluble aromatic compounds from the chopped rosemary and minced garlic directly to the meat fibers. Limiting the soak time to under two hours prevents the acid from turning the exterior mushy.
Managing Grating and Heat Application
Medium-high grill heat delivers the necessary Maillard reaction for deep exterior browning without scorching the delicate garlic particulates. Flipping every three minutes guarantees steady heat distribution across the metal or wood skewers. Applying the final salt layer immediately after removal dissolves residual grains into the surface juices.