Italian Penicillin Soup Recipe
Master the science of Italian Penicillin Soup (Pastina), a comforting, nutrient-dense broth thickened with egg, Parmesan, and tiny pasta.
- Emulsified egg yolk and Parmesan create a rich, velvety broth without heavy dairy.
- Starch gelatinization from cooking pastina directly in the broth naturally thickens the soup.
- A aromatic mirepoix provides a deeply savory, nutrient-dense base.
The secret to authentic Italian Penicillin Soup lies in the emulsion of egg and cheese into a hot, starch-rich broth. Unlike standard vegetable or chicken soups, this classic preparation relies on tiny pasta shapes—typically stelline or acini di pepe—to release starch directly into the cooking liquid, creating a naturally velvety body.
This starch gelatinization binds the liquid, preventing the egg from curdling when introduced.
When you temper the egg and finely grated Parmigiano-Reggiano into the hot broth, you are executing a delicate protein stabilization. The proteins in the egg yolk act as emulsifiers, binding water and fat molecules together, while the cheese melts into the suspension to form a cohesive, creamy matrix. If you add the egg directly to boiling broth without tempering, the proteins will denature instantly, resulting in a stringy texture similar to Egg Drop Soup rather than a smooth, cohesive emulsion.
To achieve the perfect balance, cook the aromatics slowly to build a deep flavor profile before adding high-quality bone broth. This provides a rich collagen base that enhances the soup's mouthfeel and nutritional density.
While similar in comfort to a classic Chicken Noodle Soup or the bright, egg-thickened Avgolemono Soup, this Italian version stands out due to its intense umami profile from the Parmesan rind simmered directly in the liquid.
Italian Penicillin Soup
Ingredients
- 1 tbsp extra virgin olive oil
- 1 small yellow onion, finely minced
- 1 medium carrot, finely minced
- 1 celery rib, finely minced
- 4 cups high-quality chicken bone broth (such as Aneto)
- 1 Parmigiano-Reggiano rind (approx. 2 inches)
- 3/4 cup Barilla stelline or acini di pepe pastina pasta
- 2 large eggs
- 1/2 cup freshly grated Parmigiano-Reggiano cheese, plus more for serving
- 1/2 tsp Diamond Crystal kosher salt, or to taste
- Freshly cracked black pepper, to taste
Directions
- Heat the extra virgin olive oil in a medium saucepan over medium-low heat. Add the finely minced onion, carrot, and celery, cooking slowly for 6 to 8 minutes until softened but not browned.
- Pour in the chicken bone broth and add the Parmigiano-Reggiano rind. Bring the liquid to a boil, then reduce the heat to low, cover, and simmer for 10 minutes to extract the umami from the rind.
- Stir in the pastina pasta. Cook at a gentle simmer for 8 to 10 minutes, stirring frequently to prevent the starch-heavy pasta from sticking to the bottom of the pan, until the pasta is al dente.
- While the pasta cooks, whisk the eggs and 1/2 cup of grated Parmigiano-Reggiano together in a small bowl until a thick paste forms.
- Remove the saucepan from the heat source. Ladle 1/4 cup of the hot broth into the egg and cheese mixture, whisking constantly to temper the eggs and prevent scrambling.
- Slowly pour the tempered egg mixture back into the saucepan, stirring the soup continuously. The broth will instantly transform into a creamy, opaque emulsion. Season with kosher salt and black pepper to taste, and serve immediately.
Notes
The most critical rule is to temper the egg mixture slowly to prevent scrambling.
- Use Diamond Crystal Kosher Salt; if substituting Morton's kosher salt, reduce the volume by half (use 1/4 teaspoon) to avoid over-salting due to differences in crystal density.
- Grate your Parmigiano-Reggiano from a block using a microplane; pre-grated cheese contains cellulose anti-caking agents that prevent smooth melting and cause a gritty texture.
- Do not add the egg mixture to a boiling pot. If you skip removing the pan from the heat and tempering the eggs, the high heat will coagulate the egg proteins instantly, ruining the smooth emulsion.
- The pastina will continue to absorb liquid as it sits, turning the soup into a thick porridge after 24 hours in the fridge.
- If you do not have a microplane, use the smallest holes on a box grater and whisk the cheese vigorously into the egg to ensure complete dispersion.
Serving Suggestions
Serve this soup piping hot to maintain the delicate emulsion of cheese and egg. Contrast the rich, velvety texture with bright, acidic, or crispy accompaniments.
- A side of warm Artichoke Bread provides a garlic-herb crunch that cuts through the rich broth.
- A squeeze of fresh lemon juice directly into the bowl adds a bright acidity that balances the heavy umami of the Parmesan.
- A drizzle of high-quality, peppery extra virgin olive oil over the top enhances the soup's aroma and mouthfeel.
- Serve alongside a crisp green salad dressed in a sharp vinaigrette to cleanse the palate between spoonfuls.
Storage and Reheating
Store any leftover soup in an airtight glass container in the coldest zone of your refrigerator for up to 3 days.
Do not freeze this soup. The delicate egg-and-cheese emulsion will break upon thawing, and the tiny pastina pasta will become mushy and waterlogged.
To reheat, transfer the soup to a small saucepan over low heat. Add 2 to 3 tablespoons of extra chicken broth or water to loosen the starch-thickened pasta, stirring constantly until warmed through.
Alternatively, microwave in 30-second bursts at 70% power, stirring well between intervals to redistribute the heat without breaking the emulsion.
Ingredient Substitutes
You can adapt this comforting soup to suit your pantry with a few precise adjustments.
- Stelline pasta can be replaced with acini di pepe or orzo at a 1:1 ratio, though orzo may require 2 to 3 minutes of additional cooking time.
- Parmigiano-Reggiano can be swapped for Pecorino Romano at a 1:1 ratio, but reduce the added salt slightly to compensate for the Pecorino's higher salinity.
- Chicken bone broth can be substituted with rich vegetable broth at a 1:1 ratio, though you will lose the gelatinous mouthfeel provided by animal collagen.
This Italian Penicillin Soup is the ultimate scientific approach to comfort food. By mastering the simple emulsion of egg and cheese, you can transform basic pantry staples into a rich, restorative meal in under thirty minutes. Keep a box of pastina in your pantry so you are always prepared to whip up this quick, nourishing classic.