In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatuh
Firstly in regards to Brewers yeast then it is doubtful because some scholars say it is halal and some say it is not so therefore one should take precaution on a doubtful matter and keep away from it. Bakers yeast is halal.
In regards to Vinegar then not only is it halāl but the Prophet صلى الله عليه وسلم even praised it.
حدثنى عبد الله بن عبد الرحمن الدارمى أخبرنا يحيى بن حسان أخبرنا سليمان بن بلال عن هشام بن عروة عن أبيه عن عائشة أن النبى صلى الله عليه وسلم قال نعم الأدم أو الإدام الخل
(صحيح مسلم، كتاب الأشربة، باب فضيلة الخل والتأدم به: 6/125؛ الجيل)
The Prophet صلى الله عليه وسلم said, “How great of a condiment is vinegar”
(Muslim)
If your looking to consume Apple cider vinegar then try and get a low acidity version and mix 3 tea spoons of it with 3 tea spoons of cogulated honey (thick and raw) and take with a straw to avoid tooth enamul wearing away. This has been said by many to be very beneficial.
If you want more advice on nutrition aswell as advice on worship then visit this weblink:
http://www.islamicboard.com/manners-...eir-lives.html
If you have any more questions then please feel free to ask.
And Allah knows best in all matters