Heat a sous vide water bath to 145F degrees. (see post above for additional cooking temperature options)
Place the sausages in a vacuum seal bag and seal, leaving a little space between each sausage.
Cook for 1-4 hours.
Remove from water bath and bag and place on a plate. Pat dry.
**if not serving right away, place in an ice bath for 10 minutes then store in the fridge for up to a week or freezer for up to 3 months.
Notes
While it may be natural to think you want to add beer to the bag while cooking, liquid can actually leech the flavor out of the sausages. If you want sausage flavored beer, this is great, but other wise you end up with less flavorful sausages. You can try to counteract it by adding ½ to 1 teaspoon of salt in the bag also, but I honestly think it's not worth it. Keep it simple.
The longer you cook it, the softer it will get. I like 3 hours, but cook it less for a firmer sausage, and longer for a softer one.
Use any flavor of sausage, as long as it is raw. You don't want to use pre-cooked sausages here as you won't get the same results.
You can also brown the sausages in a cast iron skillet - or serve them straight from the bag (they ugly though).
Note it is ok for sausages to be pink. Because cooking sous vide actually pasteurizes the sausage (as long as it is cooked at 140F for 2-3 hours), there is no food safety concern.
Using good quality sausage will give you good quality results.
You can sous vide sausage straight from frozen. Just add 30 minutes to the cook time.
If you're not serving it right away, place in an ice bath for 10 minutes then store in the fridge (right in the bag) for up to a week or freezer for up to 3 months.