Lasagna with Ricotta Experimentation
July 31st, 2020
This month, my wife requested a delicious layered casserole dish, lasagna, which I’ve only made once before. In general, for some reason I am drawn to the idea of food composed of texturally different layers, such as the mousse cake I made in my very first entry. The layers of a traditional lasagna: meat, cheese, noodles, each have interesting rheological aspects; here I’ll mainly focus on the layer and ingredient that I encounter hardly at all outside of lasagna, that being ricotta cheese. Partly due to scientific curiosity and partly due to an overabundance of flat lasagne noodles, this month I ended up making two lasagna dishes with the primary difference being the formulation of the ricotta cheese layer.
Ricotta cheese
Ricotta cheese has a rough texture
If you’re unfamiliar, ricotta cheese is a soft, slightly sweet cheese with a bit of a rough texture that can sometimes be a bit grainy. Ricotta can be made either from whole milk, or the by-products produced from milk during a normal cheesemaking process. The primary difference in the production of cheeses like ricotta from cheeses like mozzarella or cheddar is how they are triggered to solidify or “curdle”. Milk contains free-floating bundles of long protein molecules called micelles. Cheeses like mozzarella are curdled via the addition of an enzyme that causes the micelles to stay coherent but stick to one another and form a gel network, with relatively few calcium ions as the glue between micelles. Ricotta on the other hand curdles from milk that has been significantly acidified, usually through the addition of vinegar or lemon juice. When the milk is acidified enough, the micelle “bundles” fall apart into individual proteins which can bond to each other and reform into larger clumps. This clumpy microstructure is presumably the origin of ricotta’s grainy texture that you can see in the image on the right, and thus ricotta can probably be considered a micro- or granular-gel material as I introduced when talking about cheesecake.
Making the Lasagna
The different layer types in my lasagna: noodle, meat sauce, ricotta, and mozzerella
I didn’t strictly follow any recipe for this dish, but I looked at these two recipes for inspiration and to get a general idea of cooking times. Since I generally prefer a smoother, creamier texture in foods, I attempted blending the ricotta cheese to break it up into smaller granules, like what I did with the sous vide cheesecake after cooking. Then after incorporating Parmesan cheese and parsley into the ricotta, I assembled the first lasagna along with a steak-marinara sauce that my wife cooked up. We decided to partially cook the lasagne noodles to keep the dish from being too dry—a critique that we’d had last time. Assembling the layers was fairly uneventful, we went with a layer of meat sauce between two noodles, then ricotta, slices of mozzarella, then another noodle and so on. When spreading the blended ricotta cheese, it behaved very much like a yield-stress fluid, flowing very smoothly; I estimate that the yield stress was around 50 or so Pascals.
Lasagna number 1, the volume seemed to be reduced considerably, especially in the ricotta layers
The first lasagna turned out well, but I was disappointed in the final look which seemed a bit deflated as you can see, and in-particular the lack of volume in the ricotta layers. In general, the ricotta had retained only a little creaminess and had dehydrated significantly. Thus for the second lasagna I decided to try incorporating egg into the ricotta cheese mixture as some recipes suggest. I placed two dollops of ricotta cheese on a small plate and cooked them along with the second lasagna with an aluminium foil covering. You can see that before cooking there is a noticeable difference in the rheology; the egg-ricotta has a lower yield stress (probably around 20 or so Pascals) as we would expect since the egg contains a significant amount of water that dilutes the mixture. This ended up being advantageous in the layer assembly, as the lower yield stress made it easier to spread the ricotta cheese layer throughout the pan, filling the edges unlike in the first dish.
The blended ricotta mixtures with and without egg, before and after cooking. Adding egg slightly yellows the mixture and reduces the yield stress. After cooking, the non-egg mixture still flows fairly smoothly, the egg mixture fractures due to gelation of the egg.
Though both ricotta mixtures start out creamy, you can see that after a bit of cooking the textures and the way the materials break apart and flow is quite different. Eggs are a natural gelling agent, as I mentioned when talking about mousses. By adding egg into the cheese mixture, I presumed that it would gel during cooking, stiffening and strengthening the cheese layer, and thus hopefully maintain the volume of that layer and of the lasagna overall. This did indeed turn out to be the case as the second lasagna had much more voluminous layers of ricotta. Unfortunately, my wife and I still would not consider this lasagna to be our ideal. Adding in the egg and causing the ricotta to have a permanent gel network reintroduced a significant graininess, as you might guess from looking at how the cooked dollop broke apart under shear. Someday I’ll likely attempt to engineer a better cheese mixture by using some different additive or blending in a different cheese material. Ideally the mixture would be stiffer and stronger than ricotta on it’s own and thus resistant to being squashed between the other layers (and perhaps more resistant to evaporation), but it would still need to retain the creamy texture that we prefer, smoothly yielding rather than breaking apart.
Lasagna number 2 with a side view of the now-voluminous ricotta layers
One final note on rheology for this dish: at the very end, I finished the lasagna with parsley and a powder composed of freshly grated Parmesan cheese. Parmesan was also included in the ricotta mixture, but not at a high enough concentration that I think it would affect the rheology. In my current research I am characterizing the flow behavior of various engineered pharmaceutical powders, and thus I am also trying to gain more intuition into powder flowability and rheology. As I’m learning, the relevant metrics for powder rheology are related but still quite different to traditional rheology. In the video below I played around with seeing how well the grated Parmesan flows. Though I am still learning, I would guess that Parmesan would be classified as a “cohesive” powder (on the scale of very cohesive, cohesive, easy flowing, and free flowing), and that it has a very low bulk density. Regardless, it’s quite tasty.