If you cook sous vides as much as I do, you should have experienced the evaporation of water from food and you actually bring the water in the food boil. Why? The reason is; the rapid evaporation causes expanding steam) to damage to the food, even though it’s not hot because it is under vacuum pressure.
What happens is the cells rupture and channels are formed in the foods. Think about it, if your body’s water (inside your vessels) boils, expands and must go somewhere – so ruptures and makes channels. During sous vides cooking the foods juices leak out of the food through these channels and damage texture.
The best method to avoid damages from low-pressure boiling is by sealing foods at no more than 3°C degrees – directly from the fridge. A common sealing pressure of 30 to 50 mbar, or under 1psi. Sometimes when cooking a bag loosens during cooking, and it causes alarm. This happens because water evaporating from the food rapidly increases the pressure in the bag and after 56°C. The bags’ pressure begins to increase to 150 mbar, or over 2psi – hence a stretched and loosened bag.
Remember you can cook sous vides with water inside the bag if you have a chamber vacuum. If you plan to cook with water the easiest way is to add ice as a solid and seal and cook.