Hi! I've been making SMBC for over a year now and most of the time I've conquered the problems--except today.

I made this SMBC recipe:

3 whites

180g sugar

165g shortening

65g butter

this is the same recipe I used last week. I encountered a problem: it was soupy, fortunately, I had leftover buttercream at the time so I just added some of that to this recipe and it came out all perfect and fluffy. However, when I tried making it today, it is just not that case. It was so soupy, I've left it in the refrigerator for 2 hours, and after beating for 17 minutes, it's still soupy.

Any thoughts?

No offense, but the recipe you are using is closer to one of those cheap frostings they use at a bad supermarket that looks 10 times better than it tastes, and is meant to extend shelf life and maximize profit for the store.  A mouth full of shortening is not what I would call a good SMBC.  (And no vanilla or anything?)

I don't know for sure what caused your soup, but I usually heat my egg whites, sugar and salt using a double boiler just until I can no longer feel the sugar granules when rubbing it between my fingers.  And then beat them until stiff peaks form. Assuming you didn't overheat your egg whites, by the time you get the beating done the mixture shold be cool enough that it won't turn the fats you add to liquid. 

I don't mean to sound in any way unkind, but that recipe isn't Swiss Meringue Buttercream.  A real SMBC is egg whites, sugar, butter, flavoring.  There is no shortening in SMBC.

American or simple buttercream is shortening based icing.

You maybe be saving money using shortening, but you lose 100% quality.  When I'm asked if I use shortening, my response is if I'm not willing to stick a spoon in a can of shortening and eat it straight out of the can, then I have no business mixing it with sugar and feeding it to other people.

If you want to stick with shortening icing, then maybe try the version created by gretchensbakery.com.  She has a butter and cream cheese icing as well.  While I've never used her recipes, she has a pretty loyal following.  She provides FAQ to help clarify and troubleshoot.

Are your ingredients at room temperature? It wont come together if the butter is even a tad bit cold (for me at least). What I do is let the bowl (with the smbc mix/mess) sit on top of my oven while something's baking. Just for 3 mins or so. Just to melt the butter down a bit. And then I'll mix it up again. 
:)

Shortening is more stable than butter...there are reasons many bakers swap it out for some (or all) of the butter.  Not just to save money.  Let's not judge the shortening when you do not live in the same climate.  You are not eating it, so no need for the judgment.  I wouldn't stick a spoon in butter and eat it straight either.

@LouisNutri ‍  Was your butter too warm?  Higher humidity this time you made it?  All sugar was dissolved before adding butter?  Was the egg mixture cool before adding the butter?

Yes, it's the grocery store version of SMBC.  Duff Goldman is quoted in the following article regarding the use of Crisco/hydrogenated oils in buttercream frosting.  About half-way through the article.  Link

@vlasko @siftandwhisk ‍ that's fine. yes there's vanilla. However, I do live in a very warm & humid climate throughout the year. Most of the times I can get away with all-butter, which I do when the cakes don't require floral pipings. But since this cake I'm making is designed with about a dozen of flowers, I use shortening to help me pipe them easier--and also I have very hot hands.

@JennySamoa ‍  ‍ @640Cake ‍ yes, I brought everything to room temp. Sugar was dissolved as I have heated my egg whites up to 158F. I'm guessing the high humidity has something to do with it (we're at 97%--there's a storm). I finally fixed it, though. I just whacked it into the /freezer/ for 30 minutes, then mixed it up again.  :) :)

@640Cake ‍ The first time I ever made a buttercream I was living in Washington DC; it was the middle of summer. I've also lived in Houston Texas, and Southern California.  In Houston humility is so thick i carried an umbrella in spring and summer.

I understand humidity. I also understand stability. I also understand ingredients added to food under the guise of necessary technique.  

And having worked for the largest processed food lobbying firm in the county, I understand how the manufacturers of products like shortening spend millions of dollars to market their stuff to the public and convince congress to suppress food processing, nutritional, and safety information from the public.  That lobbying firm had an entire department of Ph.D's who produce white papers to promote their positions and give congress the talking points to defend laws that allow food processors to hide information vital to consumer choice.  The members are the Who's Who of American processed food.  They even hold conferences to teach manufacturers how to defend their companies in food poisoning cases where people, including children, die from their products.  

Judgment is not necessarily negative. Every day in life we are confronted with choices. We have to have a sense of judgment to make the best choices to live; to support our families in living healthy and happy lives; to contribute something positive to the communities where we live.

Without judgement and objection, change will never happen.  

I am quite sure you have eaten butter that has not been emulsified into a batter or frosting.  Pure butter is used on muffins, toast, pancakes, waffles, and vegetables.  And I doubt you would ever put a pat of shortening on toast and eat it, let alone serve it to someone you love.

Oh! "Soupy".. I was thinking... "curdled". I live in the tropics, so I have that issue too. Same solution.. pop it in the freezer for a bit. Glad it worked out for you! :D

Wow the misinformation came with a lot of snarky judgment on this. 

I've made an IMBC with all shortening for a photoshoot and use an all butter one all the time. You just need a thermometer. When you say it was "soupy," There are two ways this can happen. If it's too hot (or just back to room temp) it can be uniformly soupy. If it's too cold, the emulsion will break and you'll have soup with chunks of butter. it needs to be about 70-75F to emulsify properly. 

It's a good idea to have a thermometer and a heat gun, you can use the heat gun on the side of the bowl to warm up cold BC, it will break but come back together. Watch the temp, when it gets back to 73 or so let it beat for a few minutes and voila. 

Myths about a magical butter consistency for adding or your recipe or whatever are just that. It's very forgiving if the ingredients end up at room temp. 

If you don't have a thermometer at all get a thermopen for versitility, but an infrared gun version is especially for this particular task.