There is a technique that is widely regarded amongst most chefs in the industry as the proper and best method to blanch vegetables. This technique has some fancy french term, but really it is just big pot blanching. Most people believe this technique is simply dropping vegetables in boiling water and then shocking them. There are important details one must note while doing this, though. There are three details that must not be overlooked:
Salt is one of those culinary gifs from the God’s that always seems to surprise you at how beneficial it really can be. It does not disappoint when it comes to big pot blanching. When adding salt to your blanching water, you should add enough salt so the water taste like ocean water. By doing so, it seasons the vegetables thoroughly and gives green vegetables the desired vibrant green color.
- Blanching Water
I trust you already know that blanching water must come to a boil before it is ready for blanching vegetables. What most people do not know, however, is that there should be enough boiling water in your pot for it to stay add at a boil throughout the cooking process. If there is not enough, and the water may drop to a simmer when vegetables are added, add more. I have seen cooks thrown out of kitchens for blanching in less than sufficient amounts of water.
- Ice Bath
After the vegetables are done, it is important to immediately halt the cooking process. There should be enough ice and water so that the temperature of the water does not drop with the hot vegetables added.
Regarding nutrition, I believe there are many studies that have proven a correlation between cooking vegetables and decreases in antioxidants and minerals. That being said though, there is still a great deal of nutrition in blanched vegetables, especially when cooked properly.
For a great reference, Thomas Keller explains his preferred method well: