Rennet ( /ˈrɛnɨt/) is a complex of enzymes produced in any mammalian stomach, and is often used in the production of cheese. Rennet contains many enzymes, including a proteolytic enzyme (protease) that coagulates the milk, causing it to separate into solids (curds) and liquid (whey). They are also very important in the stomach of young mammals as they digest their mothers' milk. The active enzyme in rennet is called chymosin or rennin (EC 3.4.23.4) but there are also other important enzymes in it, e.g., pepsin and lipase. There are non-animal sources for rennet that are suitable for consumption by vegetarians.

Natural calf rennet is extracted from the inner mucosa of the fourth stomach chamber (the abomasum) of slaughtered young, unweaned calves. These stomachs are a by-product of veal production. If rennet is extracted from older calves (grass-fed or grain-fed) the rennet contains less or no chymosin but a high level of pepsin and can only be used for special types of milk and cheeses. As each ruminant produces a special kind of rennet to digest the milk of its own species, there are milk-specific rennets available, such as kid goat rennet for goat's milk and lamb rennet for sheep's milk.

Dirk Müller (born 18 November 1975 in Burbach) is a German race driver, driving for BMW Team RLL in the 2012 American Le Mans Series. His former Schnitzer BMW team-mate Jörg Müller is unrelated, as is French driver Yvan Muller.

In 1996, Dirk Müller won a Formula 3 race at the Nürburgring. In 1998, after a win in the GT1 class of the 24 Hours of Daytona, he scored his first title, the German Porsche Cup, to be followed by the ALMS GT title in 2000.

From the 2002 to 2005 season, both Dirk and Jörg were driving BMW 3series model E46 touring cars for the Schnitzer-operated works squad Team Deutschland in the FIA European Touring Car Championship (now WTCC). Since 2006, the team uses the new BMW 3series model E90 which is based on the BMW 320si limited edition model that has a 4-cyl engine rather than the usual 6-cyl.

The 2004 24 Hours Nürburgring was won by both Müllers (and Hans-Joachim Stuck) with the BMW M3 GTR V8 that had been raced successfully in the 2001 ALMS. In 2005, the Müllers finished 2nd behind their sister car.