Blanching is a cooking technique whereby food, usually vegetables or fruits, are briefly immersed in boiling, salted water, and then submerged in an ice water bath, (known as “shocking”), to halt the cooking process.  Blanching is utilized to:

• Soften food

• Preserve it’s color

• Facilitate the removal of skin

• Eliminate bitter flavors

Softening Food

Heat can be transmitted to food via direct contact, e.g., a grill, or indirectly through a medium.  In the case of roasting and/or baking, this medium is air.  With boiling, it is obviously water.  Water is a far more efficient medium for transmitting heat than air.  This is because water is denser.  A food submerged in water has greater contact with the water molecules than the air molecules in an oven.  Place one potato in boiling water, (212 degrees), and another in a 400 degree oven, and the boiled potato will be done in half the time or less.  Thus, boiling is a quick and convenient method for tenderizing food. 

Sometimes the food just needs to be blanched and it’s done.  For example, if you were making an asparagus salad, 60-90 seconds, (depending on the thickness of the asparagus), is sufficient to produce ample tenderness.  On the other hand, blanching can be a prelude to a secondary cooking method such as sautéing.  Sticking with our asparagus example, if you wished to sauté thicker asparagus, or white asparagus, which tends to be quite fibrous, you are likely to burn the outside before the center has cooked completely.  A brief blanch and the asparagus will sauté quicker and more uniformly.  String beans, broccoli, and root vegetables are other common vegetables that may be blanched before their introduction to the frying pan. 

Preserving Color

Green vegetables are green because of chlorophyll, their primary pigment.  Chlorophyll’s archenemy is heat which causes it to break down and form other compounds that are less green.  Despite the heat involved, blanching still preserves the vegetable’s color.  Here’s how.  Green vegetables are actually greener than they appear.  Trapped within their cellular network are gases that partially obscure their hue by refracting light.  Sort of like looking at a colored object through a veil of smoke.  The first thing the boiling water does is to allow the dissemination of these gases into the air and surrounding water.  Thus, the veggies “become” greener.  But, as stated, heat can destroy their pigments.  This is because the same heat that freed the gases is also releasing acids from the plant’s cells which will reap havoc with the chlorophyll.  But, because of the water, these acids become dispersed and diluted in the fluid medium. 

Chlorophyll’s salvation however, is short lived.  Beyond 6-7 minutes in the boiling water and acids or not, the sustained heat will eventuate in the complete breakdown of the plant’s structures and substances.  Fortunately, most vegetables can be blanched in a fraction of that time.  The final step, shocking, ensures the termination of the cooking process.  When vegetables are removed from boiling water, the heat retained within them will continue to cook them, a phenomenon known as carry over cooking.  The ice water will take care of that fly in the ointment.  But, remove the veggies as soon as they’re cold since extended soaking will also cause the color to dissipate. 

There are three other considerations vital to this process.  First, the water MUST be at a boil when the vegetables are introduced.  If not, the lower temperature will give the releasing acids more time to harass the chlorophyll before being leached into the water and air.  You must also use a large amount of water.  When you drop room temperature vegetables into boiling water they will lower the temperature of the water and temporarily interrupt the boiling process.  The larger the volume of water, the less the drop in temperature, the quicker the water can recover to a boil, and the more you will preserve the vegetable’s color.  Finally, never cover the blanching veggies or the gases and acids will not be able to escape into the air.

Skin Removal

A quick bath in boiling water is a very convenient means of removing the skins of some fruits and vegetables.  Tomatoes are the best example.  Make a small crisscross cut in the bottom of the tomato, drop it in the boiling water for 30 seconds and then into the ice water.  The skin will peel right off.  Now remove the seeds and you are ready to make tomato sauce or tomato concasśe, (peeled, seeded, and chopped tomatoes), for use in various recipes.  

Eliminating Bitterness

Some vegetables have bitter flavors, the quintessential example being broccoli rabe.  Here again, pesky acids are at work.  As with the acids hassling the chlorophyll, they can be driven off by the boiling process.  Simply blanch the broccoli rabe for one minute in salted water, shock in the ice water, pat dry and sauté.