I am going to make this icing this weekend for the first time. Can you please answer a few questions...

Do I have to have a candy thermometer?
Will this icing crust? Can I use to for piping borders etc?
Does it have to stay refridgerated?

Anything else I should know?

Thanks

I can answer some of your questions - I've never used a candy thermometer when making SMBC - I've read that once the egg whites reach the temp where your sugar is dissolved, then it is hot enough, so I just cook it til I can't feel the sugar 'grit.' As for putting in the fridge, I only do this for a short time if it is really soft. When you take it out it is hard and needs to be re-whipped until its back to room temp - it will look curdly and ruined, but it eventually whips back up. I do cover it when I leave it out on the counter. I haven't tried piping with it yet and I haven't gotten it to crust either.. I mostly use it under fondant and as filling - it is delish, especially with choc cake!!!

I don't use a candy thermometer - I just whisk and cook until it's frothy, hot and no more sugar graininess. I just use the whisk to drip some on my finger - it should feel very warm, and if you rub it between your fingers, you shouldn't feel any sugar. It will not crust. You can refridgerate to firm it up, but will not be able to smooth with a paper towel or roller - you have to smooth it when you're icing it with a hot (not wet) spatula. I have left it out overnight (in a cool pantry) with no problems - and also had leftovers covered on the counter for another day or so and it was fine. You can make flowers and borders with it - but won't be as stiff as crusting buttercream.

Also - the only way I've had success it to use cold butter straigt from the fridge. It curdles and looks ruined after you think it should be done - but it's because it's too cold. I use a hot wash cloth then and wipe around the bottom of my mixing bowl to warm it some until it fluffs up and comes back together like buttercream. I also find that I need more icing than with regular buttercream. I used two batches on a 10" cake and barely had enough to make flowers for the top, borders a some vines.

I use a thermometer, because to reach a pasteurization temperature you have to get to 160. MOST people will never get sick off of raw egg whites, but children, the elderly and those with compromised immune systems have a slight risk, and it's one I don't want to take.

You can pipe with it...just might take some practice to get a feel for it.

Food rules say it should be refrigerated within 2 hours like all perishable foods. But some websites and resources quote longer times, like 6 hours. I used to be paranoid until I read more, and now I refrigerate up until about 2 hours before serving, let it come to room temperature, and then tell everyone it has to be refrigerated if there are leftovers. If it's under fondant, it takes a LONG time to come to room temperature.

Swiss meringue buttercream is what I use most of the time. I heat the sugar/egg white mixture until it reaches 150. Pasteurized egg whites can be used but I personally find it compromises the taste and texture. It does not crust but pipes beautifully. I don't switch to the paddle until after the butter is incorporated and the buttercream "comes together". I then switch to the paddle to smooth it out. Works like a charm every time. I have left it out overnight in a cool spot (my garage) during the cold weather months, but not in warm weather. I read it can be left out for two days but am also afraid of the health hazard. I also store it in my wine cooler when I'm working with it - keeps it cool but it doesn't get firm. I also leave it in there overnight for use the following day. It takes a lot less time to come to room temperature. I also store my cakes in the refrigerator and take them out a few hours before serving. I hope this helps you.