Sous vide without a vacuum sealer: the water displacement method

Submerge the food in a sealable bag, most of the way closed but with one corner or a few inches of the seal left open, and lower it slowly into the water bath, keeping that open corner above the surface the entire time. As the bag descends, water pressure on the outside of the bag squeezes it inward, and since the air inside has nowhere else to go, it is forced up and out through the open corner as bubbles. Once the bag is submerged right up to that last open section and no more air is escaping, seal the remaining opening while it is still above the waterline. What is left is a bag with most of the air removed by external pressure rather than by a pump, which is close enough to a true vacuum seal for a short cook.

• Use a bag with a genuinely flat bottom seam, since a bag that wants to fold or bunch traps air pockets in the corners no matter how carefully you lower it
• Lower slowly. Dunking the bag quickly traps air rather than pushing it out ahead of the submersion line
• Leave a generous unsealed margin at the top, since a short margin runs out of room to work with before all the air has escaped

Any freezer weight zip top bag will get you through a single cook, but two things matter more than brand: the bag needs to tolerate sustained heat at your bath temperature without softening or leaching anything into the food, and the seal needs to actually hold shut once submerged rather than working itself open under water pressure. Purpose built reusable bags such as Platinum Pure reusable sous vide bags are made from platinum silicone rated for sustained sous vide temperatures and close with a mechanical clip rather than a fold-over zip seal, which removes the most common failure point of using a generic kitchen bag for something it was not really designed for.

Two situations push you toward an actual sealer. The first is a long cook, several hours or more, where the extended time gives a mediocre seal more opportunity to work loose or let water seep in, a bigger problem on a collagen-heavy cut you are holding for many hours than on a quick steak. The second is freezing: water displacement removes most of the air but rarely gets a bag as tight as a true vacuum, and the air that remains is exactly what causes freezer burn during storage, showing up as dried, discolored patches after a few weeks. For either of those situations, a real sealer, either a suction machine like the compact Anova Sealer or, for anything involving liquid, a chamber machine, is worth the cost. Our guide to how vacuum sealers work covers the mechanical difference in more detail.

Some air almost always remains even with a careful water displacement seal, more than a machine sealer typically leaves behind, so floating is common with this method and worth planning for rather than treating as a failure. Sous vide magnets clipped to the bag, or a plate or rack weighting it from above, push the bag back under the surface and keep the whole piece of food in contact with moving water instead of resting against a pocket of trapped air. Skipping this step on a bag that keeps rising to the surface means part of the food is genuinely spending the cook at a lower effective temperature than the rest, whether or not you used a sealer to close it.

It is workable but fussier than for a plain piece of meat, because liquid near the open corner of the bag can spill out as you lower it rather than staying put the way solid food does. Angling the bag so liquid pools at the sealed bottom rather than near the open top, and leaving a wider margin of dry bag above the food before you start, both help. For a genuinely liquid dish, soup, a wet brine, or a heavily marinated cut, a chamber sealer handles it far more cleanly than either water displacement or a suction machine, since it never pulls air, or liquid, through the bag opening at all.