I'd always assumed that things cooked sous-vide (which translates as 'under vacuum'!) needed to be under a good vacuum for the most efficient heat transfer into the meat, since air is less convective than water. I also thought there might be a hygiene issue with having the meat exposed to the air in the bag.
However, in the video on this Kickstarter page (at around 1.00), she simply puts the steak in a sealed Ziploc bag and then into the water bath, without evacuating the bag. So, are my concerns unfounded?
Best Answer
Yep, Ziploc bags are fine although make sure you have ones that are appropriately heat sensitive for whatever temperatures you'll be cooking at. There's a good guide on the Cooking Issues blog:
http://www.cookingissues.com/primers/sous-vide/part-ii-low-temperature-cooking-without-a-vacuum/#sectionII3b1