Hi, I’m new here and hoping some of you can offer advice. 

I’ve been working on improving my smoothing skills with various different buttercreams (I make Swiss meringue usually, but also Italian and TCB’s Silk Meringue).  The common advice that I see for these types of BC’s is to warm a bench scraper with hot water, dry it, and use that to scrape smooth on a turntable.  However, whenever I try this method my Buttercream gets a mottled appearance.  It looks like the buttercream is partly melting as soon as I scrape it and the melted part turns a different color.  The effect is most pronounced on colored buttercreams, but the same thing is happening with my normal undyed vanilla buttercream, so I don’t think the gel paste food coloring is the problem.  When I let the bench scraper cool, then it seems to be dragging through the buttercream, roughing it up. 

A few points of clarification - I do several coats, chilling thoroughly in between, trying the warm bench scraper only on the final coat.
My bench scraper is very thick metal, blunt on the edge, rather than sharp.  Could this be part of the problem? 
As for the recipe itself, I weigh ingredients out in grams and check temps with my candy thermometer or thermapen. 

I’m pretty frustrated, since so many of you seem to have no problems with this method and I really don’t understand what I’m doing wrong!  Please help!
I’ve tried to attach a picture of my latest cake disaster - which looked far worse after I spent a hour trying to smooth it than before.

This is not unusual with an italian meringue buttercream; and my experience mirrors yours.  It’s much worse with colored or chocolate buttercream.  What I’ve found that helps - it’s not a cure-all - is adding more fat in the form of melted white chocolate or using a very soft, “fluid” type of shortening (e.g., FluidFlex) in small amounts to make the buttercream a little more “supple”.  With darker colors, I don’t even try using meringue buttercream; I have resorted to using the Whimsical Bakehouse buttercream (shortening and butter based) to get the really really dark colors and I put it on over the meringue buttercream.

I find that I have better luck (less problems) when the buttercream is freshly made.  I keep a bench scraper expressly for smoothing the sides of cakes, and it’s got a beveled edge and if you spin the turntable quickly, it works well. I don’t have to warm it at all.  If I have to, I’ll use a very very sharp paring knife (the straight part of the blade; try to get one just for this purpose, it took me a year of searching to find the right type of knife) to smooth out any remaining “bumps” or imperfections.

Two thoughts come to mind, both things I learned from making tiered cakes.

  -First, buttercreams only last so long before they need to be re-beaten.  This means that if you beat the buttercream and immediately frost your cake, you have a window of time in which you can continue to work the buttercream on the cake before it turns spongy and needs to be re-beaten.  Sorry, I don’t know the exact amount of time, it seems to vary.  But you have to frost and then smooth one tier at a time, then re-beat before doing the next tier. And no matter what, don’t go back and re-work it later or you’ll get dark patches and streaks wherever you touch the buttercream.  I learned this the hard way on my first three-tiered cake.  If you’re chilling and smoothing repeatedly, this is very likely your problem.  Everywhere the scraper touches, the sponginess of the buttercream means that it loses some air bubbles and darkens. 

  -Second, the angle of the bench scraper is everything.  If you hold it at a 90 degree angle, it will not work well to smooth the buttercream.  You have to hold it at a more acute angle (perhaps 30 degrees).  I’ve never worked with a heated scraper, I’ve found that a flat angle and working quickly so that the buttercream doesn’t turn spongy are all that’s needed.

If you want to practice a little, bake or buy a small unfrosted cake and use a little leftover buttercream to work on technique.  First try the flat angle for smoothing the buttercream.  Let it sit for a while and then try to work it to see what happens. You’ll understand and be a pro.

Thanks so much!  Those are really helpful suggestions.  Fortunately the wedding cake I’m making for next weekend is fondant (and for my very laid-back best friend), but I’ll have plenty of chances to practice.  It’s good to know that other people have had similar challenges - at least the proves I’m not insane.  It’s neat that you mentioned the Whimsical bakehouse - that was actually the very first cake decorating book I learned from.  I’d tried the House buttercream one time when I was first learning,  but had no clue how to work with it, since it doesn’t crust or really set up very well.  Have to try it again, now that I know more . . . 

One question - when you add white chocolate, do you use the “real” white chocolate, the kind made with cocoa butter?  Or candy melts type white chocolate? 

Thanks again!

Real white chocolate

this is a very interesting topic, and i think you all got it right.  i also get streaks when i smooth with a heated icing spatula.  it is TRULY a matter of temperature.  if too cold, the buttercream will be grainy and develop marks.  if too hot, the buttercream will be blotchy.

you need to pay attention to 3 temperatures:  the temperature of the cake (i like to work on well chilled cakes), the temperature of the buttercream, and the temperature of your room.  buttercream will be the smoothest when at 75 oF (i can’t tell you exactly, it just it is when it looks and feels right), or a little lower or higher depending if the cake is chilled or not or if your room is cold or warm).

the reason of applying several coats, and refrigerating is between, isn’t to make it smoother, it is to make it more even, cover holes, and build a nice edge or shaping the cake.  if the previous coat isn’t well refrigerated, when you apply the next coat, the first coat will come right off.  on the contrary, the purpose of heating the icing spatula isn’t to make the buttercream smoother neither, it is to continue to shape the previous coat.

find the temperature when the buttercream is the most pliable and try to maintain this temperature as you apply the final coat.  in most cases, since most kitchens are warm, you need to chill the cake.  but if your kitchen is air conditioned or around 70 oF or lower, there isn’t as much need to chill the cake between coats.

i hope i make sense.

Thank you all for the advice - I really appreciate you taking the time to explain!