Proceed through the ventilation shaft until you've reached the cold store. Go across the room, until you've reached the gate with a lever. Jump on the lever... and quickly run to the left, as your old pal the cook will come out of the elevator door. Enter a box in the cold store and wait for the cook to take the cheese. Once he's far enough, crouch and head for the elevator. Take the elevator up and hide in a recess in the wall.
After a brief moment, the cook will come and open a way for you. Follow him and hide under the table near the entrance. Wait for the cook to focus on the meat and run for the tables at the wall. Now, wait for a good opportunity to proceed, climb the table and go through the open window.
Pick up the can from the floor and throw it at the button. This will draw the cook's attention - run quickly to the table where he prepared the meat and grab the key. Take the key to the elevator and go down. Use the key on the padlock to the right, enter the room, and hide in a container.
Once the coast is clear, leave your hideout and go through the hatch in the wall. You'll find yourself at a trash heap. Approach the ladder on the wall and climb it. Enter the duct and follow it until you reach the room with a pile of dirty dishes. This time, you'll have to get past a room with two cooks.