General tips
The single biggest bolognese mistake is rushing the soffritto. Sous vide can't fix flat aromatics - that flavor base of carrot, celery, and onion has to brown deeply on the stovetop before anything else goes into the bag. Twenty minutes of patience here is worth more than two hours in the bath.
Use a mix of meats. Traditional Bolognese uses 60% beef chuck, 30% pork, and 10% pancetta. The pork adds sweetness, the pancetta adds savory depth, and the chuck provides the body. All sirloin makes for a thin, joyless ragù.
Add the milk before the wine. Sounds backwards, but the milk coats the meat proteins and prevents them from seizing up when the acidic wine hits. The result is a tender, almost creamy texture. Skip this step and you'll get pebbly meat.
Cook at 165°–170°F for 12–18 h. Shorter than that and the connective tissue won't melt; longer and the meat starts to lose its structure. You want individual fibers, not paste. Stir once at the halfway point if you can.
Anti-tip: don't serve Bolognese on spaghetti. Use tagliatelle or pappardelle - flat, wide noodles whose sauce-grabbing surface area was literally designed for ragù. Spaghetti slips out from under the meat. This isn't snobbery, it's geometry.
Rich & Deep tips
Use mixture of beef and pork for best flavor
Milk tenderizes the meat and adds richness
Red wine adds depth; white wine is traditional