A container has a product chamber for containing a product. The product chamber has a product opening that opens into the exterior. A closure member is releasably mounted on the product opening. The container further includes an additive chamber for containing an additive, and a pressure valve that connects the additive chamber and the product chamber with each other. The pressure valve has a closed position when the pressure inside the product chamber is higher than the pressure inside the additive chamber, and an open position for discharging additive from the additive chamber into the product chamber when the pressure inside the product chamber is lower than the pressure inside the additive chamber. The pressure inside the product chamber is higher than the ambient pressure and the pressure inside the additive chamber is both lower than the pressure inside the product chamber and higher than the ambient pressure.