The Trial and Error of Making Liquid Spherical Ravioli

As any scientist will tell you, experiments fail more than they succeed. In fact, if you just looked at the amount of time scientists spent on failed experiments compared to successful experiments, you might be tempted to conclude that the real task that scientists are paid for is to fail. However, this failure is necessary. What leaps forward would we make by just repeating old experiments over and over again to prove we could? It’s in the taking of old experiments, analyzing the mechanism, and postulating the results with new compounds and setups that creates leaps forward.

I had done some reading about the making of liquid spherical pea ravioli (Molecular Recipes), but not being a large fan of peas, I decided to try and make some adjustments to the recipe. I wanted to make spherical spinach ravioli.

Attempt 1:

As usual, I started by making the calcium lactate bath and storing it in the refrigerator. I then started with fresh baby spinach, and used the food processor to chop it up.

I ended with ~6 ounces of chopped spinach.

Using a mini blender, I mixed ~8 ounces of water with ~ 2 g of sodium alginate. I heated the water-sodium alginate mixture on the stove while stirring to create a clear viscous liquid.

I added the chopped spinach to this mixture and allowed it to simmer on the stove top for a while. When I removed it, I used the blender once more, and ended up with less than 7 ounces.

The last step was to filter the mixture through a sieve.

This was when I realized I might have a problem. The liquid was too viscous to be easily strained with the strainer I own. After waiting about a half and hour and seeing no filtration occurring, I decided to hope for the best and go on to the next step.

Using the spoons that came in my Molecular Gastronomy kit, I went ahead and spooned out tablespoons of the spinach-sodium alginate mixture into the calcium bath. The results were less than ideal. Blobs that were mildly reminiscent of spheres formed, however they collapsed into a mushy runny liquid as soon as removed from the calcium bath. Even when allowed to “cook” in the calcium bath for up to 15 minutes, this occurred.

So, my first experiment with liquid spherical ravioli failed. I had many factors to consider, and came up with a few things that I believe were factors in the failure. The most important of these were the viscosity and the pH.

As discussed previously, sodium alginate creates a gel upon contact with calcium (Ca2+). However, this only occurs with contact, so the outside of a sodium alginate droplet or sphere will create an alginate-Ca2+ gel matrix, while the inside, which is free from calcium contact, remains liquid (at least for a bit). This is the mechanism for how a liquid center sphere is created.

However, alginate only forms a gel with Ca2+ when it has a negatively charged oxygen atom free to bind with the positively charged Ca2+. This is the case when it is in the Na+ Alginate- form. However, when introduced to an environment where the pH is low (acidic), there is a preponderance of H+ around. This favors the reaction of sodium alginate –> alginic acid. Alginic acid not only doesn’t have a negative charge, allowing it to bond to the Ca2+, but it forms a solid itself. This means the solution will start to gel by itself. This can happen if you mix an acidic food with sodium alginate. (Note: you can also see premature gelling if the water used to create the sodium alginate mixture is tap water and not filtered due to calcium in the water supply.) It is therefore important to monitor the pH of the foods used when using sodium alginate calcium mediated gelling.

There are many food pH charts available online where one can check the pH of the food they are using. After checking one, I learnt that spinach has a high (basic) pH. This is referred to as alkaline (Food pH Chart). It’s possible that being alkaline somehow affected solution and led to decreased gelling action, but not due to the above acidic-mediated disruption pathway. It is possible that perhaps the alkaline spinach bonded to the positive Ca2+ and disrupted the matrix of alginate-Ca2+ that usually forms. Without being sure of the exact mechanism, my suggested remedies to this problem would be to add an acidic compound that would even out the pH, using pH strips to test for the solution pH. The best solution would be to use an acidic compound that would also be complementary in flavor to the spinach.

The other issue, and in my mind probably the bigger issue, was the viscosity of the solution. The less viscous the alginate solution is, the greater the effect the liquid center has. In addition to this, viscosity can effect a reaction and the physical properties of its product.

In this case, the fact that the spinach “soup” wouldn’t strain was probably a sign. Although the desired viscosity for the solution/bath is more/less, there is such thing as too viscous. (10 Tips) Although I cannot be sure, I imagine the viscosity of the spinach-alginate solution as well as the lack of uniformity may have led to uneven alginate distribution, creating a dense sphere when in the bath that could not hold together out of it. To fix this issue, next time I would create a spinach soup that is blended to the point of being creamy, and with a higher water content in order to make it less viscous.

Attempt 2:

A few days later, I was thinking about my last failed experiment and feeling a little bummed out. I decided to try it again, this time using the tips I had troubleshooted from my last attempt. I still was opposed to using peas, but decided to try with edamame.

Using edamame would help both of the issues I had. Edamame is mildly alkaline compared to the more strongly alkaline spinach. In addition, blending peas tends to make a more uniform solution.

After making the calcium bath, I boiled the edamame for about 10-15 minutes. After they were soft, I took them out of the boiling water. Using an immersion blender, I blended them to create a uniform edamame blend.

Separately, I added 2 g of sodium alginate to 400 mL of water. Using an immersion blender, I combined the two. I then allowed it to heat on the stove top, until it became a clear solution.

———–>

To this, I added the edamame and again combined them using an immersion blender to create an edamame-sodium alginate solution. The final step was to pass the solution through a sieve.

With everything ready, I got the calcium bath out of the refrigerator and began to try my second attempt at spherical liquid ravioli.

Yatta! The result was liquid spherical edamame ravioli. Although this attempt was also slightly viscous, the result was much more successful than attempt #1.