This is an important question and one that gets to the root of much of our cooking. We cannot always explain why. In cooking, intuition or a gut feeling, directs many of the paths we choose to wander.
When we started looking at asparagus and the cooking of it, we were not happy with the traditional method of cooking it in a large pot of salted, boiling water. First of all because when we in cook this way, many nutrients are leached from the vegetable end up in the cooking water. Second of all, in order for us to keep a large rolling boil in the pot, we can only cook a few pieces of asparagus at a time, which is not the most efficient way of getting things done. Last but not least, we have continued to find ourselves in more and more remote locations, so we often have to procure good produce in bulk and find ways to preserve both quality and flavor. We wanted to find a method which would preserve the essence of the vegetable without destroying its clarity and freshness.
We were introduced to the concept of compressed fruits by an article about Thomas Keller. We don't know if he invented the method, although upon reading about the process-- vacuum sealing fresh melons to compress their cell structure and change the texture from raw to firm, yielding a juicy and concentrated end product, we were inspired. Upon discovering the technique we were inspired to put all kinds of fruits through the vacuum process. Yet, while our results were good, we knew that our Food Saver just was not as powerful as the commercial vacuum sealers that really make magic happen.
After working with fruits, our minds wandered. We wanted to know what would happen if we tried green vegetables. I gave it a shot and the results were good. Then we called up a few friends (Sean and Shola) who had professional vacuum machines and asked them to test the process on asparagus. Their more powerful machines yielded better results, although the vacuum still did not break the cells enough to create the texture of a cooked vegetable. As we continued to read about preservation methods and discuss the concepts with others, the idea of freezing the vegetable after it was vacuum sealed and then letting it thaw came to mind. The freezing of the asparagus under vacuum controls the growth of ice crystals, keeping them small and allowing for them to just pierce the cell walls. Upon thawing the vegetable, the result should imitate that of a perfectly blanched vegetable.
We've all tried the process and the results are amazing. It works. You can "cook" green vegetables in the freezer. No fresh flavor is lost, the essence of the vegetable remains intact, and they are tender and delicious. It's a much faster process than blanching large quantities of vegetables. This method also yields better results than traditional blanching. There's no danger of overcooking and it allows us to capture a vegetable at its peak and be able to present it at it's best. Finally, in our remote locations it allows us to have fresh tasting vegetables on hand at all times.
What's the purpose of a brief soak in salted water? It allows us to uniformly season the vegetable. In situations where we work with white asparagus and for our experiments with root vegetables, we use a sugar and salt solution to sharpen and balance the flavors in inherent in these vegetables. It simply adds more flavor to the finished product.