The blanching water may be used several times. Steam blanching is an alternative to water blanching. Only a small amount of water is used, and the vegetables are held in a basket above boiling water in a covered kettle. Some nutrients are lost during blanching because they leach out of vegetables sitting directly in the boiling water. Fewer nutrients are lost from steam blanching because the vegetables are not sitting directly in the water.
Steam blanching takes a few minutes longer than blanching in water.
The heat distribution often is uneven with steam blanching, especially with leafy vegetables like spinach. The cooling step immediately following blanching is especially important if you are to have high-quality frozen vegetables. Cool blanched vegetables as quickly as possible to prevent overprocessing. Frozen vegetables will often be of poor quality if these steps are not followed properly. They can become mushy and watery from overblanching or too little cooling and draining.