It's quarter-final day. Two Michelin-starred chef Marcus Wareing, the formidable Monica Galetti and MasterChef's seasoned diner Gregg Wallace push the professional chefs to the limits as they hunt for Britain's next culinary superstar. The chefs' first challenge is the Invention Test - this one will push them to their limits. Whilst the chefs are used to cooking with the finest ingredients, they are instead faced with the kitchen scraps and trimmings, from which our judges expect them to create one course that truly impresses. Their ingredients include bones and offcuts, fish skin, overripe fruits, cooked rice, cheese and stale bread. It's a daunting challenge but the price is high - after judging their dishes, Marcus and Monica will decide who is worthy of continuing in the competition. Next, the chefs face the terrifying task of showcasing their skill to three of the UK's hardest-to-please restaurant critics. With a semi-final place at stake, the chefs have an hour and 15 minutes to create a stunning two-course menu which will determine their MasterChef future. Sitting in judgement of their culinary abilities are critics Tracey MacLeod, Jay Rayner and William Sitwell. Only the most exceptional chefs can make it through to the semi-finals and move a step closer to the coveted title of Professional MasterChef 2014.