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room temperature, one breast per bag

chicken breast + salt + pepper on both faces, then sealed with the air displaced, one to a bag and laid flat. Pound or press a tapering breast to an even thickness first: the bath cooks by conduction from the outside in, so an uneven breast has a thin end that is already soft while the thick end is still climbing, and thickness is the only variable that changes the time. Butter and a thyme sprig can go in now. Roasted garlic is safe here; raw garlic is not, because a sealed oxygen-poor bag held for hours at 145°F is the specific environment botulinum spores are waiting for