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Slicing Onions for Onion Soup

When slicing onions for making onion soup, how should the onions be sliced -- pole to pole or crosswise? In the past, I've used the slicing disk of my food processor to slice the onions crosswise. But now I'm thinking this might be a mistake -- that they'll have better consistency, and maybe even taste better after caramelization if I slice them lengthwise, pole to pole. What are your thoughts?

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  1. I slice onions the normal professional way: halve them vertically (pole to pole), so you have the root end to keep each half together, then make 3+ slightly incomplete horizontal slices parallel to the cut end on the board, then slice vertically perpendicular to the pole-pole axis, as it were. Chopping involves an intermediate set of vertical slices parallel to the pole to pole axis.

    To tame the power of onions that will be eaten *raw* (it wouldn't matter for cooked slices), I normally just rinse them well in cold water, but Cooks Illustrated explains the following in their Jul-Aug '09 issue:

    "The onions sliced pole to pole were clearly less pungent in taste and odor than those cut along the equator. Here's why: The intense flavor and acrid odor of onions are caused by substances called thiosulfinates, created when enzymes known as allinases contained in the onion's cells interact with proteins that are also present in the vegetable. These reactions take place only when the onion's cells are ruptured and release the strong-smelling enzymes. Cutting with the grain ruptures fewer cells than cutting against the grain, leading to the release of fewer allinases and the creation of fewer thiosulfinates."

    2 Replies
    1. re: Karl S

      Karl, Cooks Illustrated disagrees with you. In their French Onion Soup recipe (Jan/Feb 2008), they made a point of specifying pole-to-pole slicing: "Slicing against the grain results in cooked onions with a lifeless, stringy texture. Onions that are cut pole to pole maintain their shape during our Best French Onion Soup's (page 13) long cooking process." In that version, they call for yellow onions whereas their initial recipe (Jan/Feb 1999) found them "only mildly flavorful", instead specifying red onions because they are "intensely onion-y, sweet but not cloying, with subtle complexity and nuance." A splash of balsamic vinegar was included at the end to restor the color to the red onions, which turn gray during long cooking.

      1. re: greygarious

        Oh, yes, now I recall that. Thanks for the additional information. I do remember the red onion advice, which is what Alton Brown also recommends. Alton Brown also has the single best method for making FOS: using a large rectangular electric skillet (the kind that were fasiononable in the '70s, but are still available at modest procies) to caramelize. I've even taken this inspiration to make FOS in my smaller electric fondue pots when I am making smaller quantities.

      1. re: todao

        The process of caramelizing the onions in that recipe seems so long and labor intensive as compared to doing it all on the stovetop. Have you tried it? Is the end result noticeably better?

        1. re: CindyJ

          I've made this CI soup twice. Long-yes. Labor intensive-not at all. And just about guaranteed not to scorch the onions.

      2. I recall being told at cooking school specifically to cut onions pole to pole for soup. They keep they shape better.

        1. pole to pole, avoids that stringy-ness

          FYI- i've found that i tear up less when i slice onions wearing my contacts as opposed to my glasses

          1. Thanks to all who validated my hunch. Pole to pole it is!