I am making this recipe for pulled pork, planning to do 24 hours at 75 deg C. After coming home from work, I discovered I did not suck the air out properly and there is a big bubble in the bag, causing it to float to the top and for the top of the meat to be not submerged properly. I have now put a bowl on top of it to weigh it down for the next 12 hours. Will it still be safe to eat? Will it taste good?
Air in the bag can be a result of two things: (a) you did not properly eliminate it, or (b) bacterial growth. The main problem is that the portion of the protein that has floated above the water will not be at the same temperature as that which is under the surface. We don't know what portion of the meat was above the waterline, nor for how long. So, I won't make any guesses about safety or quality. Given your description it is difficult to determine whether your issues is related to (a) or (b)...or maybe even both, if you did not notice floating immediately. In the future, firstly make sure you seal properly, by using a vacuum machine, or barring that, submerging your bag, which has been sealed most of the way, in water to force the air out. At the last moment, seal the rest of the way. You can inhibit bacterial growth on long cooks at low temperatures by either giving the protein a quick sear on all sides, or a 10 second dunk in boiling water. If you are using sturdy vacuum bags, you can dunk in boiling water after you bag the meat.
Even if your food bag has air in it and floats, the heat will transfer through the plastic into the food and into the moist air in the bag and it will equalize, especially if the food pot is covered. Isn't this similar to a Dutch oven?. If you suspect that I'm wrong measure that temperature in the bag after sitting in the bag in the bath for an hour