I am new to baking and was wondering if anyone has ever used piping gel to write Happy Birthday on a cake iced in Buttercream . And if so does the piping gel affect the taste of the buttercream. 

Thanks

I have never tried to write with piping gel. I did use clear piping gel one time and put blue dye on it to use it for a water scene on top of my cake.  I did not get to taste it but the people who I made it for never complained about the taste of the piping gel.

Have you tried adding a little bit of milk to a small amount of buttercream which will make it flow easy and use it with a small round tube for writing. You don't want too much but just enough to make it easy to write with. Try it and write on wax paper to see how it works before writing on actual cake. Not sure what round tube others use but I think I use a #4 round tube. 

Piping gel should not affect the taste of your buttercream, especially if you are just using a little bit to write happy birthday.

If you're worried about it, put a little piping gel on a little bit of buttercream and taste it before putting any on the cake.

Maybe you could use tinted buttercream to write the message?

Thanks for everyone's response. I will try them all on parchment paper and see which ones work the best.

Thanks