Who doesn’t like bubbly, melty, brown cheese on top of a pizza, lasagna, quiche or just about anything else? Even though I’m not the biggest melted cheese fan (I prefer a good Dutch or French cheese, at room temperature), it does make food look good and make a lot of people happy. But why does cheese turn brown at all on top of a hot dish? And why does it bubble? And why do some melt better than others?!
Time for some answers!
What’s cheese? – The science perspective
Cheese starts with milk. Milk though contains a lot of moisture, so one of the main objectives of cheese making is getting rid of a lot of that moisture. While getting rid of the moisture, we want to hold on to the fats and some of the proteins. A specific group of proteins in milk, the casein proteins, can be triggerd to do exactly that. By adding an acid or enzyme, the proteins will curdle, taking along with them the fats and several other components, but leaving out a lot of moisture.
Using these same principles a lot of different cheeses can be made, each with a different moisture and fat content, flavour, texture, etc. As a result, not all cheeses work the same and not all cheeses are appropriate for creating a nice crusty layer of cheese on top of your oven dish.
Why does cheese turn brown on top of a quiche?
When a quiche or pizza for that matter, are baked in the oven the cheese changes in several ways as well. First of all, the increased temperature of the cheese will melt the fat and evaporate the moisture in the cheese. Also, the increased heat will initiate the (widely discussed on this website) Maillard reaction. During the Maillard reaction proteins and sugars react into brown colour molecules, causing a lot of different foods to brown (bread, dark roux, etc.).
Not all cheeses brown equally. This actually depends on a variety of factors. First of all, enough proteins and sugars have to be present. It was shown that the use of different micro organisms to make the cheeses, could actually influence the sugar content and thus influence browning.
The moisture content also influences the extent of browning. The Maillard reaction generally does not occur (or slower) if too much or too little moisture is present. The perfect moisture content will depend on the specific food though.
Last but not least the fat content influences browning of cheese. If there is no fat at all in cheese the cheese is quite prone to burning. The fat makes a thin layer on top of the cheese, keeping moisture inside for long enough (not drying the cheese out completely). This helps with browning of the cheese. Too much fat on the other hand will only form puddles of fat and does not improve browning further.
Then why does cheese on top of a quiche or pizza bubble? That links back to what we discussed in the previous section: the evaporation of moisture. Despite the removal of a lot of milk during cheese making, there still is quite a bit of moisture in cheese. The exact content strongly depends on the type of cheese though. An old parmezan is a lot drier than a fresh mozzarella.
When this moisture in the cheese evaporates in the oven it can be caught by the cheese structure. It’s similar to the moisture caught in a bread dough when baking bread. If the cheese is not flexible at all, the moisture will remain caught inside the cheese until the cheese burst and it comes out. You won’t see this. However, if the cheese is a lot more flexible the cheese will move with the gas, in other words: the cheese puffs up and forms bubbly cheese. Only when the pressure of the evaporated moisture is higher than the flexible cheese can handle will it burst. This does result in nice and bubbly cheese toppings!
Spinach quiche recipe & Choosing cheese topping
One the foods that look good with brown melted cheese are quiches. The recipe I share below is based on one from Sally’s baking addiction. As you can see on the photo below I used a pre-grated mix of cheeses. Using a combination of cheeses is great to overcome the challenges mentioned above. You will see the cheese mix includes mozarella (which melts well, but is pretty bland), gouda (which has a nice flavour and melts ok) and emmentaler (which agains, melts ok, but also has a nice extra taste to it).
- There are several pie crust recipes on the website already, look for the links below the recipe.
- 450g frozen spinach
- 1 clove of garlic
- 3 eggs
- 100ml milk
- 3 pieces of sun dried tomatoes (feel free to add twice as many)
- 75g of grated cheese (I used a mix of Emmenthaler, mozzarella & regular Gouda)
- In order to keep the spinach flavourful, I prefer not overcooking it. So thaw it gently, in a frying pan on the lowest heat in 15-25 minutes. Add the chopped garlic during thawing.
- Once the spinach has melted, leave it on a little longer to evaporate some more moisture. A lower moisture content will help prevent a soggy pie crust.
- Cut the sun dried tomatoes in small pieces and mix through the spinach.
- Wait until the spinach has cooled down before mixing in the milk and eggs (else the eggs will set straight away).
- Make your pie crust in the meantime. Since this filling tends to be quite moist I prefer to blind bake the crust a little longer (160C, 25 minutes).
- Take the pre-baked pie crust and pour the filling in. Cover with the cheese and bake in the oven at 160C for 45 minutes (until the top is a golden brown).
This types of pie always have a risk of ending up with a soggy crust instead of a super crunchy one.
Browning of cheese during high temperature pizza baking, research article from 1994
A model of mozzarella cheese melting and browning during pizza baking, research article from 1998
A review article on melting of cheese (covers a lot of the topics we discussed in this post): Factors influencing the functionality of mozzarella cheese.