I think I dound the real reason:
How can I make my semen taste better?
Question:
My girlfriend and I give oral sex on each other and she really wants to be able to swallow my semen. I saw your page about oral sex and taste but it didn't say if there are ways to make it taste better. Can drinking sweetened juices make it taste better? Are there any sex products (like tasty sugary lube gel?) to make it taste better? Or would it be ok to use something like sugar-water as an oral lube/sweetener?
Answer:
After much research, I still have not come across any scientific experiments pertaining to how to make semen itself taste better. But, there are a lot of personal opinions in the rumor mill coming from people that have experimented on their own. Many people suggest eating or drinking things with high sugar content. The male could eat pineapple or other fruits, or drink fruit juices, in order to sweeten the taste of his semen.
Another suggestion is to maintain a vegetarian diet, or simply cut down on meat. Some people suggest cinnamon, lemon or green tea. One could also use a sweetened lube to try to mask the taste of the semen, or wear a flavored condom so there is no contact with the semen at all. Using a condom does have its advantages because in addition to escaping the taste of semen it reduces the risk transmitting STDs via oral sex. There are also a few products on the market that claim to improve the taste of semen such as Sweeten’d Blow and Semenex.
My advice to you is to experiment. Experimenting is the best way to discover personal preferences relating to your sexuality. Everyone is different, and every couple is different as well. I recommend that you try a few of these various techniques and see which one works best for you and your partner. And, if you come to any conclusions, please let us know what you think works best so we can share the information with others who are interested.
-the Sexperts
http://www.soc.ucsb.edu/sexinfo/?article=faq&refid=688 
