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When garnished with onion, a martini is called a Gibson martini. Use small pearl onions, which are often marketed for cocktails. They usually come in a jar and are often pickled in brine. If you're in a pinch, try garnishing with a slice of regular white or sweet onion, but remember that it might not quite give you the taste you are hoping for. Onions are sometimes pickled with paprika or turmeric, along with the pickling brine. If you have onions that are adding too much of the wrong kind of flavor to your drink, rinse them off quickly with cold water. Keep in mind that rinsing them will take away some of the flavor, so only do it if you feel it's absolutely necessary. You have the choice to skewer the onions or place them directly in the drink. Ask the drinker which they prefer. Rest the toothpick against the side of the cocktail glass when you serve the drink. The skewer is convenient because it allows the drinker to easily pull the onion out of the drink if they want to eat it.
Make a Gibson martini with pearl onions. Rinse the onion off for a subtler taste. Spear the onion with a toothpick or drink skewer.