• Preparing the equipment
  • Grease is the biggest enemy of meringue and the slightest speck on the bowl or whisk could render all your hard work useless. And, it's not just about oil or butter. I'm also talking about egg yolks. Egg yolks have fat and the tiniest amount in your egg whites will not whip into meringue no matter how long you whip.
  • So, before you start making any meringue buttercream. First, wash and clean the bowl and whisk well (especially if you last used it to make buttercream or similar). Then, separate each egg in a small bowl first and use only the eggs which have been separated carefully. Save the others for an omelet or other uses.
• Double boiler
  • Basically, a double boiler is just two pans that fit perfectly together. One on top of the other. We often use this indirect heat method when we want to melt chocolate, or in this case, gently cook eggs with sugar. The steam caused by the water in the bottom pan is just enough to melt the chocolate or egg without burning or overcooking it.  I wrote more about double boilers in a previous post - What is a Double Boiler Method?
• Prevent deflating meringue
  • It is best to start whipping eggs at medium speed then increase speed as you go for the best meringue. This meringue will not lose volume and will hold much better. 
• Prevent soupy buttercream
  • The meringue must be cool completely before you add the butter otherwise you will have a soupy mess.
• White Swiss meringue buttercream
  • Often, buttercream tends to get a yellow ting and because of the color of the butter. However, I do not usually have this problem because I do get white butter (see pictures). So, here's a little trick you can use to neutralize the yellow by adding a tiny bit of blue or violet to it. 
    In fact, this is very commonly used when painting walls white. You add a tiny bit of blue or violet to neutralize the yellow. BUT A TINY DAB IS ALL YOU NEED or you will end up with a slight tinge of blue or violet in the buttercream. So, remember, a dap or smear is all you need.
• Prevent separating buttercream
  • Do not beat buttercream while it is very chilled. Since the cold fat in the butter separates from the liquid and the emulsion you just created breaks. Ideally, you can just let the buttercream rest outside the fridge for a while until it's not hard. Or, you can use a hair-dryer to gently warm the outside of the bowl until you see the edges of the buttercream soften a bit. Then, whip it with a paddle attachment.

Storage

• Meringue Buttercream will keep at room temperature for a few hours in any weather. I know those who enjoy good weather are able to keep Swiss or Italian meringue buttercream out for up to 2 days.
• It should be treated just as butter; If left out in high temperature or humidity it will melt just like butter.
• It can be kept refrigerated for up to one week or in the freezer for up to three months.
• When frozen, it is best thawed in the fridge overnight. Whip with a paddle attachment for about 3 to 5 minutes to restore consistency.

Buttercream Flavors

• Dark, Milk, or White Chocolate SMBC? 
  • Add 200 grams melted and cooled chocolate to 4 cups of SMBC. Combine well. 
• Caramel Swiss Meringue Buttercream or Salted Caramel SMBC –
  • Add 1 cup caramel sauce to 4 (to 6) cups of SMBC. For salted add a tablespoon of rock salt. Combine well. 
• Butterscotch SMBC –
  • Add 1 cup butterscotch sauce to 4 (to 6) cups of SMBC. For salted add a tablespoon of rock salt. Combine well. 
• Lemon SMBC  –
  • Add ¼ teaspoon lemon juice to 4 (or 6) cups buttercream. You can also add up to ½ if you want a very lemony buttercream. 1 teaspoon of zest can also be added if you don’t mind the zest in the buttercream. And, ¼ teaspoon lemon extract will enhance the flavor even more. 
• Orange Swiss Meringue Buttercream  –
  • Add ¼ cup orange juice,  and ¼ teaspoon orange extract to 4 (or 6) cups buttercream. 1 teaspoon orange zest can also be added. 
• Fruit Flavors – Blueberry, Raspberry, Blackberry, strawberry –
  • Add 1 cup fruit puree to 4 (or 6) cups buttercream.
    I love adding a fruit filling instead, which makes it slightly sweeter, and yet, more vibrant in color. 
• Dulce De Leche SMBC  –
  • Add 1 cup dulce de leche to 4 (6 cups) buttercream. 
• Coffee or Espresso SMBC –
  • Dissolve 1 tablespoon coffee in ¼ cup hot water or use ¼ cup espresso. Cool completely, then add to 4 (or 6) cups buttercream.
• Mocha SMBC Buttercream
  • Add 200 grams melted and cooled chocolate to 4 (or 6) cups coffee SMBC.
• Peanut Butter SMBC 
  • Add up to 2 cups of peanut butter to 4 (or 6) cups of buttercream.