I was asked to make a vanilla cake with strawberry buttercream.  I created my own recipe for the buttercream that on taste test came out delicious (several neighbors did a taste test for me!).  I used tip 1M to pipe on flowers.  The flower itself looks great; it's just the end when I removed the tip looks less than perfect.  It looks like I just yanked the tip away when in reality I actually took extreme care to release the pressure then try to release the flower from the tip.  When I tried to pipe stars to see if it would keep happening there were gaps in the center of the icing.  Any ideas why this is happening?  I appreciate your help!

Air bubbles?

I also think there are air bubbles in the icing and maybe consistency is not right, not enough icing sugar. 

So you're making rosettes?  When you remove the tip don't pull up.  After you've finished the outside and you've stopped squeezing keep moving in the circular motion and go back to the "tail" and tuck it in to the side of the icing.  Hopefully it hat makes sense.

It difficult to say not knowing if you made a real buttercream or a powdered sugar & shortening icing.

powdered sugar is a mix of cornstarch and sugar, so it thickens.  For fluid piping, the icing needs to be a medium consistency.  

I use IMBC, but I keep a tub of Wilton icing for practice.  There's a marked difference between the piped icings. The Wilton does not pull away cleanly and the edges are not as sharp. 

Thanks!  I appreciate the response.  It's definitely not air bubbles because the rest of the icing looks smooth and correct.  It's just the "tails" so I think I will try the circular motion at the end.  

Just to check the recipe - it has 1 cup each butter and shortening (equal ratios - super hot here right now so I need the icing stabilized), 1 cup strawberry puree, 1/2 tsp strawberry extract, 4 tbs milk, and 3 lbs (12 cups) powdered sugar.  It seems to be the right consistency for piping but maybe I am wrong.  Should I adjust the recipe?

Thanks again!  I appreciate the help!

Is the strawberry purée chunky? When you first said that, it made me think it might be getting clogged up  

beyond a technique issue, like @Pastrybaglady  said, or a consistency issue, like @Norcalhiker  said...

sounds like your icing might be starting to crust too soon. are you taking care to keep it covered before putting into piping bags? you can try swapping the milk out for heavy cream...the cream will extend the time it takes for the icing to crust over. 

The puree is boiled down to pure liquid so it is not getting clogged.  I think it could be crusting too fast.  I'll try heavy cream in the next batch of icing.  And definitely work on my technique!

I normally wouldn't stress so much but this order is for a woman who is in the food industry.  She knows all the best bakers in the area and she chose me to make her daughter's birthday cake.  No pressure right?!?!

You ladies are such a help!

You may want to check the temperature of your puree before you add it to the mix.  Starches absorb moisture and heat makes a starch thicken more.  Cornstarch will begin to thicken at 95 degrees.  Commercially produced powdered sugar is about 3% cornstarch.

The interesting think about cornstarch is something called non-Newtonian fluid property.  Essentially when pressure is applied with force to dissolved cornstarch, it reacts not like a liquid, but a solid.  Think of water--water is so fluid you can't pick it up.  But if you squirt it from a hose with a nozzle attachment, it will shoot out in a solid stream.  Once the pressure is released, water becomes fluid again.  

If you make a 2 parts cornstarch 1 part water solution, you can form the liquid into a ball in your hands, then release the pressure and it comes apart.  The force of pushing the icing through the piping bag may also cause the non-Newtonian effect, making your icing momentarily stiffer.