The semi-final stage continues with just eight chefs left in the running for the 2021 title. Tonight, the first four face off over two challenges in the hope of making it to finals week.Their first challenge sees them cook outside the MasterChef kitchen for the first time as they head to the heart of industrial east London to open a pop-up at a warehouse microbrewery. In recent years, the pop-up scene has exploded in the UK, giving innovative chefs the opportunity to deliver a unique dining experience in dynamic locations. Working on makeshift workstations with limited equipment and no ovens, the chefs must rise to the challenge and adapt their fine dining style to impress 14 esteemed guests from the world of pop-up kitchens. They have three hours to prepare and deliver one skillful pop-up dish that showcases star quality and is memorable on the menu for all the right reasons.In their second challenge, the four chefs return to the MasterChef kitchen to face a cook-off. They have one hour and 45 minutes to create one dish of exceptional standard. Once the challenge is over, Marcus, Monica and Gregg taste their efforts, and for one chef it's the end of the road. The other three will be through to finals week.