You do not swirl a sparkling wine like you would a still wine. Swirling will cause the CO2 to dissipate too quickly. The bubbles will help release the aroma (primary scents) and bouquet (underlying smells that develop as wine ages) and carry the scents to your nose. The type of champagne glass will often have an impact on the intensity of the aroma and bouquet. Tilt the glass and put your nose in it. Sniff, inhale and smell. The sparkling wine should smell clean. You can inhale a couple of times, or just take a few short whiffs, whatever feels best to you. Opening your mouth while you sniff may also enhance the experience. You may want to try sniffing at different points in the glass. Associate the aroma/bouquet with scents that are familiar to you. Laboratory testing through gas chromatography has actually proven that wine contains molecules matching those in certain fruits, flowers and other substances. Some common descriptors used for scents found in sparkling wine include apple, pear, fresh baked bread, brioche, citrus, mushrooms, bread dough, a hint of honey, subtle strawberry, some straw or hay, herbal notes, almond… to name some. You may be able to further define the aroma/bouquet. Is the apple smell reminiscent of baked apples or green apples? Is the citrus lemon or lime? The yeasty, bread like scents are the result of autolysis (the consequence of aging on dead yeast cells after the secondary fermentation has taken place in the bottle). An unpleasant off odor may indicate the sparkling wine has a fault.
The palate is what characterizes sensations in the mouth. It is more than just taste; it also includes feel. Take a small amount of wine into your mouth. One of the first things you notice as you taste it are the bubbles. Observe the sensation as they flow over your tongue and gums. Are they soft and velvety or aggressive and tart? As the bubbles begin to dissolve, what do you notice? Sweetness is detected toward the front of the tongue, acidity is along the sides and bitterness is near the back. Are the elements balanced? Fine champagne may have different attributes. It can be dry, crisp, creamy, delicate, elegant, fruity, display minerality, be full or medium bodied and have differing degrees of autolysis. What you smell may or may not be similar to what you taste, but the descriptors are fairly similar (ripe pear, apple, biscuit, brioche, citrus, mushrooms, strawberry, straw, herbs, almonds, etc.) The finest champagne will become smoother and develop the greatest amount of autolysis as it ages, displaying more fresh bread, brioche, or nutty characteristics. If the wine is out of balance because there is too much alcohol, it can feel heavy or invoke a slight burning sensation. When you swallow or spit (perfectly acceptable, especially if you will taste several wines), a fine champagne should have an enjoyable, lingering finish. The best has wonderful complexity and depth that has been stored and aged appropriately and will lure you back for more. You will likely notice something different every time you smell or taste, like a mystery slowly unfolding before you.