Rich media is 1% yeast extract, 2% Peptone, 2% carbon source. Yeast is very easy to pellet (one minute at 5000rpm is enough )so I guess what you grow is not actually yeast if it is not pelletable in this condition...
I agree with Dominique. You may have a contaminated culture and not be able to pellet the cells you want. Try the rich media he suggested and add some antibiotic to the plate to avoid bacterial growth.
For DNA isolation, I normally use YPED Broth or YGC Agar to grow the cultures. It is easy for me to centrifugate the broth medium after activating the cultures. Some species like Kluyveromyces marxianus and Saccharomyces cerevisiae were too easy to get the pellet. However, this was not the case for D. hansenii and some Pichia spp. Therefore, I collected the cells after straking on YGC/YPED Agar plates. The resultant DNA was so much more clear. In your case, I don't know your purpose to grow the yeast cell, but it is better to work with both broth and agar medium.
I recommend to determine, what yeast do you want to culture. Completely different culture media should be used for yeast utilizing phenol as a substrate in comparison to Saccharomyces cerevisiae grown in media with sucrose as a substrate. When you know what yeast you want to cultivate, you can choose an optimal culture medium for given yeast strain.