Getting rid of a commercial/plastic taste in icing?

The ingredients they post are:

• 1 cup solid vegetable shortening
• 1 teaspoon Wilton Flavor (vanilla, almond or butter)
• 7-8 teaspoons milk or water
• 1 lb. confectioners' sugar
• 1 tablespoon Meringue Powder
• pinch of salt (optional)

I would make the following suggestions based on these ingredients:

• It's not really butter cream icing if you're using vegetable shortening. You'll get far superior flavour by using butter. Pure butter may have trouble holding its shape, but you should have no trouble at all switching to a half-and-half mixture. This ratio won't change the colour much either.

• I've never personally cared for the Wilton flavourings and suspect that is a major part of the problem here. If you're using the vanilla, it's not real vanilla, it's imitation vanilla extract; pure vanilla extract is dark brown and would colour the icing. Their almond flavour also seems to taste nothing like normal almond extract, and the butter flavour is thoroughly pointless (just use butter!).

  You can use real vanilla extract, but it will definitely darken the icing. You can try to compensate with an icing whitener, but those things are intended for slightly-off-white icings and probably won't get you all the way to white. Alternatively, you can use pure almond extract instead of the imitation; it is actually clear to begin with.

  Or, better yet, you can just change your brand. Lorann makes a bunch of concentrated flavouring oils that might taste less fake. If you go to any baking supply store you'll probably see other brands as well. Try a few until you find one that you like.

• You don't say whether you're using milk or water, but use whole milk or even cream if you can; don't miss an opportunity to lay on the fat (and therefore flavour).

• Finally, a lot of people (me, for example) find the taste of meringue powder to be disgusting. You don't need it, and the vast majority of buttercream icing recipes don't contain it.

  If you really want a meringue-based buttercream, as opposed to a simple buttercream without any egg products at all, then just go for broke and make it from an Italian meringue; whip some egg whites to soft peaks, then whip boiling sugar syrup into the eggs until the mixture stiffens, and afterward incorporate the butter and other flavourings.

  I know, they're going to tell you that it won't be stiff enough. But stabilizing a meringue is dead easy; just bloom some gelatin in the cold liquid (water/milk/cream) before you incorporate it¹. The more gelatin, the stiffer it will get. Don't overdo it because if you add too much gelatin, you won't even be able to get it out of the bag (this has happened to me). A 1% ratio should be plenty.

Making a great-tasting decorating icing is easy. Stiffness isn't usually the problem, colour is. If you want brilliant white icing then you have to make certain tradeoffs. If you're willing to settle for a cream colour (or slightly whiter, with a whitener) then you've got nothing to worry about.

_{1. If you're not starting with a hot meringue, then be sure to heat the liquid with bloomed gelatin to dissolve before adding it to the icing!}

It's been a few years since I took cake decorating courses, but when I took Wilton 2 and 3, my instructor gave us an alternate recipe to use. It might not crust up quite as fast as the one with meringue powder, but it was fine for the humidity that we have in Maryland. (although, I admit, DC metro, not eastern shore). I've made it a few times using meringue powder in place of the cream of tartar ... I assumed it had to be a mistake the first time I made it, and both work fine. I haven't done a side by side comparison to see which one crusts up first, but I'm guessing the meringue one.

To respond to some of the comments made so far ... Wilton Buttercream is not a real buttercream ... it is stable at warm temperatures, and is much less finicky when trying to make flowers, etc. It's also pure white, so you won't get off colors when you are trying to tint it. I'd leave out the butter flavor, as you don't need it ... The sugar and fat pretty much hide any flavors you have.

And one other possible source of off flavors -- oxidized shortening. I keep a can that I use for greasing pans if I'm not specifically using cake release, but for frosting, I use the sticks. They're tightly wrapped, so less exposure to air, and easier to measure.

Instead of using the manufacturer's recipe, try this one. It has perfect consistence for decorating.

You can use milk or water. Water works great and tastes fine. It won't spoil.

• 2 LB bag Dominos conf sugar,
• 1 cup regular Crisco,
• 2 teaspoons good clear vanilla,
• 2 teasp good butter flavoring,
• 1/2 teaspoon almond flavoring (opt), 1 Tablespoon Meringue powder (opt),
• 1/4 teasp salt,
• and 1/2 cup water.

Cream Crisco and meringue powder few minutes. Add flavorings to water. Beat in 1/2 powder, then 1/2 water, add remaining powder, then rest water. Beat 3-5 minutes. Stores well in fridge and freezer.

Many recipes call for double amount of Crisco and wonder why it has a greasy taste. This is great and crusts well. You can adjust the flavorings according to taste. Add more sugar for making roses.

Aaronut nailed the answer. He's 100% correct. Now, for my 2 cents.

The three obvious problems are the shortening, the flavoring, and the meringue powder. That's obvious just looking at the recipe. Even Wilton agrees, amusingly (I'd cut out the vegetable shortening entirely.) This is more my style.

But you wouldn't need someone to tell you this if you tasted. For a no-cook item like icing, you need to TASTE the ingredients. Taste the flavoring. Stick your finger in it and lick it. Is it good? Does it have a weird chemical flavor? Taste the nasty nasty vegetable shortening (then throw it out the window. Yuck.) See how it's not as good as butter? Taste the meringue powder. Blech.

Every flavor you put in icing is going to shine through. I live in a humid area, so I constantly need to tinker with consistency, and that is impossible if you don't understand your flavors. Don't be afraid to taste it at every step of the process, and, if it tastes bad when you finish, throw it out and start over. Don't ruin good cake with mediocre icing.

I would start by looking at the confectioner's sugar. Often these come with additives like corn starch to keep from caking, which to me gives an "off" taste. Try to find one without the anti-caking agent, or make your own. Caster/superfine sugar could be a viable substitute as well, which would avoid the issue.