Italian buttercream is one of the most popular styles of frosting for pastry chefs, adventurous home cooks, and aspiring cake decorators. It starts with a meringue of whipped egg whites warmed with a hot sugar syrup, which is then enriched with butter. At its most basic, it's a three-ingredient buttercream that takes about 30 minutes from start to finish, giving it an obvious allure.
Unlike Swiss buttercream, for which the meringue is cooked over a hot water bath, Italian buttercream is merely warmed with the hot sugar syrup, but the results are equally fluffy, light, and easy to work with. The primary difference is that Swiss meringue is fully cooked, while Italian meringue is not.
Health department guidelines suggest that egg whites should be held at a temperature of 132°F (56°C) for 6.2 minutes to be fully pasteurized. My recipe for Swiss buttercream reaches a final cooking temperature of 185°F (85°C) over the course of 10 minutes, so it more than exceeds those safety standards. Meanwhile, even with a 250°F (121°C) syrup, Italian meringue falls well short of that goal, as the syrup cools rapidly when it hits the bowl.
I’ve clocked Italian meringue at around 134°F (57°C) after the syrup is added, but that’s a temperature it maintains for a few seconds at most. It’s therefore unclear what temperature the meringue actually reaches when the syrup is added, and whether or not the time-and-temperature combination is sufficient for pasteurization.
Even so, here at Serious Eats, we disregard the FDA guidelines on meat-cooking temperatures and consume raw-egg products all the time—in mayo, in tamago kake gohan, in steak tartare, and even in cocktails. Are there risks associated with undercooked eggs? Yeah, and if you have health concerns or immune-system issues, you should probably avoid them (or otherwise follow your doctor's orders).
I can honestly say that Italian buttercream is my least favorite of all possible styles. It’s messy, and pouring 250°F syrup into the bowl of a running mixer can be dangerous for newbies. Plus, because the safety of the eggs' cooking temperature is in doubt, and because cakes are best served at room temperature, Italian buttercream poses some difficulties in storing a cake.
Among European styles of buttercream, Swiss is my go-to at least 75% of the time;* it's just as easy, just as fast, safer, and it can be held for much longer without those food-safety risks.
* I probably make French buttercream 24% of the time, with honey or maple Italian buttercream covering that remaining 1%.
So why am I even writing this guide to Italian buttercream? Well, there’s no denying its popularity, so it seems shortsighted to ignore it altogether. But, perhaps more importantly, Italian buttercream lends itself to certain flavors that Swiss buttercream does not.
Specifically, you can use other syrups, like maple, honey, and agave, to flavor an Italian buttercream—because the syrup is heated first, any excess water in those syrups is cooked off before it’s poured into the egg whites, allowing them to fully aerate. In a Swiss meringue, the egg white syrup isn’t cooked enough to drive off the excess water of those syrups, which introduces instability to the meringue.
The reward of using syrups like honey and maple is remarkable, producing a boldly flavored and super-aromatic buttercream. It's a feat that neither Swiss nor French buttercream can match. So, if you're looking to make something with that bottle of agave nectar from Mexico or the acacia honey you picked up in France, Italian buttercream is the best way to showcase it in a frosting.
Because these natural sweeteners contain impurities, they can foam significantly during the cooking process, necessitating a much larger pot than hot syrups made from sugar and water or corn syrup. For that reason, a three-quart stainless steel saucier is the smallest possible cooking vessel that can be used in this recipe. It's okay to use a larger pot if you don't have that exact size; just bear in mind that the increase in surface area may shorten the cooking time, so be on your toes.
Equipment issues aside, assembling the buttercream is laughably easy. Boil the liquid sugar to about 230°F (110°C), then start whipping the egg whites in a stand mixer fitted with a whisk attachment. When the syrup hits 250°F and the egg whites are foamy and light, the two are combined.
The only real trick is to make sure the syrup is drizzled down the sides of the bowl, as it may strike the whisk attachment when poured near the center. If that happens, the spinning whisk may fling dangerously hot syrup from the bowl, where it can make a terrible mess and cause injury. But if you work slowly and cautiously, the risk can be all but eliminated.
Once the hot syrup has been added, continue whisking until the meringue has cooled to somewhere between 85 and 90°F (29 and 32°C). This should take only about five minutes, but stand mixers with footed bowls may retain heat and slow the cooling process down (a major reason why we don't recommend that style of stand mixer).
Once the meringue has reached the proper temperature, it's seasoned with salt and enriched with unsalted butter softened to about 65°F (18°C). Like Swiss buttercream, Italian buttercream is a game of averages, so these temperatures are guidelines rather than rules.
I like working with a warm meringue and cool butter, because they provide a larger margin of error, but it's absolutely possible to make a successful buttercream with hot meringue and cold butter, cool meringue and warm butter, or any combination in the middle. The goal is to hit a final working temperature of about 70°F (21°C).
At this temperature, the buttercream will be silky-smooth and light, weighing about six ounces (170 grams) per cup. If colder, it will be much denser (as heavy as eight ounces per cup), potentially with a greasy, curdled, or wet texture. If too warm, it may become too soft, runny, or soupy for use.
Fortunately, these problems are easily resolved, so never throw away a "broken" buttercream. All it needs is a little TLC: a bit of warmth if it's too cool, and a bit of cooling if it's too warm. It's really that easy.
If the buttercream is soft or soupy, it's simply too warm, so toss it in the fridge for about 10 minutes, or place it over an ice bath for a few moments, just until a film of buttercream begins to harden around the bowl. Then re-whip for about three minutes to homogenize the temperature and texture from edge to center.
Conversely, if the buttercream is dense, greasy, or curdled, it's too cold—nothing more. Toss it over a steaming water bath just until you notice a bit of melt around the edges, then transfer it back to the stand mixer and re-whip.
For beginners, nailing the perfect temperature can be a bit of a balancing act that involves overcompensation on either side. But with experience, it becomes completely intuitive, making it easy to adjust a buttercream until it's the perfect texture for spreading over a cake.
Like Swiss buttercream, Italian buttercream is a great make-ahead frosting that can be refrigerated for up to a week or frozen for several months, provided that it's stored in an airtight container. (My preference is for a large, freezer-safe zip-top bag.) When thawed back to 70°F (21°C), it can be re-whipped to restore its light and fluffy texture for use.