Paddy McGuinness is fully immersing himself in the festive spirit as he explores a huge chocolate factory in Belgium. With lots of taste tests to enjoy along the way, he embraces the fantastic processes and surprising science that enable the epic production lines to knock out four million individual chocolates every day. And they're especially busy in the run-up to Christmas.Paddy is at the Guylian chocolate factory, on the outskirts of the very Christmassy-sounding city of Saint Niklas in Belgium, to learn how they produce chocolate seashells ready for the Christmas rush. He begins by meeting Kevin Stevens at the factory's intake bay to welcome in a bumper delivery of hazelnuts from Turkey. Kevin tells Paddy that the hazelnuts are a key component in the praline filling inside each of the chocolate shells.Once the sacks of nuts are safely inside the warehouse, Paddy is chuffed to learn that the size of the nuts is very important. They must be between 8 and 11 millimetres; any bigger and they'll be too fatty, any smaller and they'll be too dry. Luckily, Paddy's nuts make the grade, and he follows 7,500 kilograms of them inside the factory.Resplendent in his factory hairnet, Paddy's next stop is the intriguingly named Kettle Room. As he enters, he is blown away by the delicious smell and intrigued by the traditional-looking machinery. With the help of an automated shoot, a torrent of hazelnuts and refined white sugar cascades into one of six copper kettles. The kettles are heated to around 140 degrees Celsius, which roasts the nuts to draw out their subtle flavours. At the same time, the sugar caramelises. The result is a beautifully sweet, nutty mixture. The problem is, it's too chunky to be anywhere near a smooth praline paste. To solve this, the mixture is sent through a mincer, which produces a fine crumb with a melt-in-the-mouth texture. Paddy is in heaven in his first of many taste tests. Then things get even better, as milk chocolate is added to produce a velvety smooth hazelnut praline.With the centre of his chocolates made, Paddy is guided to the enormous, automated seashell production line. Two thousand six hundred moulds in the shape of different seashells continuously travel through the line. As they make their way along, half receive a splash of white chocolate and half a splash of milk chocolate, then an additional layer of chocolate is added to create the marbled effect that the finished chocolates are known for. In a surprising twist, each and every mould is flipped upside down, letting the chocolate pour out. But Paddy needn't worry; it's all part of the plan to ensure the perfect amount of chocolate is left in the moulds to create the outer shell. After travelling through a cooler, it's time for the hazelnut praline that Paddy helped to make earlier. Eighty-eight taps gently release an average of 6.8 grams of the praline filling into each half of the chocolate shells. Then, to complete the seashell shape, the two moulded halves are joined together. Just three hours and five minutes after the start of production, Paddy delights in the sight of finished chocolate seashells streaming past him, and he can't help but get stuck into one - or two!As the final act of this sweet Christmas drama draws to a close, the chocolates head to the packing area, where they're dropped into blister packs and then slid inside cardboard boxes and sent to the dispatch area. And because the site is so large, there's only one way to get there – by bicycle! The six-year-old Paddy couldn't have dreamt of a better Christmas present: riding a bike through a chocolate factory.Four hours and twenty-five minutes after the start of production, Paddy waves off a lorry load of chocolate from one of the loading bays. From the factory in Belgium, the seashells head off all over the world. But it's the Brits who eat the most at Christmas, putting away a whopping 44.7 million chocolate shells over the festive period!Elsewhere in the episode, Cherry is also in Belgium, at another massive chocolate factory, learning how they produce the white chocolate used in Paddy's chocolate seashells. And she enlists the help of mathematician Bobby Seagull to explore the art, or rather the maths, of Christmas tree decoration.And historian Ruth Goodman is in Belgian too, exploring how Belgian chocolate has become world-famous, and she delves into the European origins of Santa Claus.