For even cooking, try to use oxtail pieces that are similar in size. This may require cutting some pieces.
While some fat on oxtails adds flavor, you want to make sure they’re more meaty than fatty.
For maximum flavor, make sure the oxtails are well coated in the braising liquid before sealing the bag.
Removing the air from the bag is an important step that should not be skipped to avoid bacteria entering the bag.
Since we’re cooking these oxtails for up to 48 hours, you’ll want to keep an eye on the water level of the water bath. For food safety and even cooking, the bag of oxtails should be fully submerged in water.
Cover your water bath with foil to help prevent evaporation or add more water to the bath.
The bag may float in the water bath as the oxtails cook. To prevent floating, you can weigh the bag down with something heavy like a sous vide sinker weight.
If air gets in the bag, just open the bag, let the air out and reseal it. This works for vacuum seal or ziplock bags.