When sharing food or drink with another, one can assume the purity of their mouth. Human saliva is pure [Tahtawi/Shurunbulali, Hashiyat Maraqi al-Falah]. If you are reasonably sure that they just took an impure substance in their mouth – such as wine or pork – then avoid sharing with them.
If after taking in the impure substance one drinks water, swallows their saliva, or spits out their saliva – their mouth is again pure, and sharing a drink with them is not an issue [Tahtawi/Shurunbulali, Hashiyat Maraqi al-Falah].
Mere ingesting of impermissible ingredients doesn’t entail it being impure.
Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani
Shaykh Yusuf Weltch is a graduate from Tarim; a student of Habib Umar and other luminaries; and authorized teachers of the Qur’an and the Islamic sciences