There are only 180 Master Sommeliers in the world. In order to achieve Master Sommelier certification, sommeliers, or wine stewards, must undergo rigorous training for various amounts of time and pass four levels of examination.

William Sherer is one of these distinct professionals. He has been the wine director at such world-renowned establishments as the Ritz Carlton New York and Aureole, chef Charlie Palmer’s restaurant at the Mandalay Bay Resort in Las Vegas. Sherer now lives in Northern California where he directs the wine programs at Redd, a Michelin star restaurant that combines local seasonal ingredients with international flavours, and sister restaurant Redd Wood, a chic pizzeria featuring wood-fired pizzas and homemade pastas. Both eateries are located in Napa Valley, California’s most famous wine region, which attracts almost five million tourists each year.

As a sommelier, answering questions is a central part of Sherer’s job. So we asked him to address some of the most common queries people have about wine.

What is terroir?
“It’s the flavour that’s imparted from the land where the grapes are grown and from the winery,” Sherer explained. ”So, each region in the world has a signature flavour, within the same grape variety…The opposite of terroir is commercially-stripped flavour, where you can often make a wine that tastes like it could be from anywhere.”

Is wine vegan?
The short answer is no. “Wine is not a 100% pure thing,” Sherer said. “It does have some natural chemicals that are added to keep it looking and tasting good. To clarify wine, winemakers will [often] use proteins as a natural fining agent.” For example, egg whites can be added to wine barrels because they naturally attract wine sediment particles. Other common proteins are those extracted from fish.

That said, there are some specialty wineries that go out of their way to produce wine using vegan methods. Frey Vineyards in California’s Mendocino County makes vegan wine by clarifying their white wines using an earth clay called bentonite and leaving their red wines unfiltered.

Is wine gluten-free?
The short answer is yes. The basic ingredients of wine are naturally gluten-free. However, certain wines may contain trace amounts of gluten from additives (such as clarifying, colouring or flavouring agents), from wine barrels constructed using paste made from gluten, or from yeast that was cultivated in a medium containing gluten.

Why does wine get better with age?
“When a wine ages, it gains complexity. The molecules are actually reforming and changing, breaking down and going from very primary flavours to more complex flavours,” Sherer described. But not all wines taste best when aged for a very long time. “Each wine has its own drinkability curve. Wine [is] born at a low drinkability level, and sometimes quickly or slowly gets to the perfect stage, and then drinkability goes down after some time.” At the end of the day, it’s all subjective, he stressed. “Part of it is cultural. For instance, the British are known for liking their wine old, and probably Americans like to drink their wine a little younger.”

Is wine good for you?
In moderation, yes. The skin and seeds of the grapes used to make wine have antioxidants that work to prevent cellular damage. Health studies have found that these antioxidants may prevent blood clotting, inhibit the growth of cancer cells and reduce the risk of heart disease. “Red wine has a lot more antioxidants than white wine because it has more contact with the grape skin [during the winemaking process],” Sherer said. Positive health effects have also been traced to the alcohol present in wine, since small amounts of alcohol can raise “good cholesterol” and thin the blood.

How do you store wine?
“You want to store a wine bottle on its side to keep the cork from drying out. If the cork dries out, it will lose its elasticity and fail, letting air in.” Another way to keep the cork in contact with the wine is to transfer the leftover wine into a half-bottle. “Storage temperatures are also very important. If you don’t have wine storage, the coolest place is in the basement or inside a closet in the centre of a building. This way, the wine won’t be affected by the outdoor temperature as much.” If the only place you have to store wine is the [regular] refrigerator, Sherer said, that is probably okay too. “Most professionals will say that a refrigerator isn’t good because the temperature is going up and down too much, and that it keeps the wine too cold for too long – but that has not really been proven to have a huge impact. The bigger impact comes from too warm a temperature.” One final tip Sherer has for storage is that white wines are more sensitive to warmer temperatures than red wines.

Does wine go bad?
After being opened, wine will eventually go “bad”, turning into vinegar. Bad wine, Sherer said, can eventually start smelling like varnish or nail polish – even worse than vinegar. There are different techniques to make wine last, though, all of which aim to keep oxygen out of the wine. “The most common is to displace the oxygen with a heavier gas. Another way is to move the wine into smaller containers so you have less air space.” The former method can be done using wine preservation sprays or vacuum wine stoppers.

Why are wine glasses so big?
“Two reasons: one is to allow the wine to create a space for aroma, since part of the enjoyment of the wine is the nose. [The second] is about how the wine flows onto your palate,” Sherer said. For example, Champagne can actually be better enjoyed from a wide glass, versus the ubiquitous Champagne flute. “The Champagne flute was designed to minimize the surface area to keep the bubbles in the liquid. But a wider-mouth glass allows the whole palate and tongue to enjoy the full flavours of the wine. The finest Champagne houses in France will tell you that,” Sherer explained.

Glassware companies go to great lengths to accommodate wine drinkers, Sherer said. The Austrian glassware company Riedel, for instance, makes a glass for dessert wine that is curved into a tulip shape in order to launch the wine away from the tip of the tongue and onto the middle and side of the tongue. Playing into the popular idea that tastebuds at the tip respond to sweetness, this is meant to reduce the wine’s sweet taste; (scientifically, though, all areas of the tongue are responsive to sweet, salty, sour, bitter and umami flavours).

What is good wine?
There are three characteristics that good wines tend to share, Sherer explained: “Harmony, complexity and uniqueness.” Harmony means that the elements of a wine work together in balance, complexity means that a wine has a variety of flavours and uniqueness is what sets one wine apart from all the rest. “Customers often ask me, ‘Why do people pay thousands of dollars for one bottle of wine?’ It’s about tasting a unique moment in time.” Of course, only personal taste determines whether a 100-year-old special vintage Bordeaux tastes better or worse than a 10-year-old Bordeaux.

How do you open a wine bottle without a corkscrew?
Yes, even Master Sommeliers recognize the occasional need to break the rules in a pinch. “There are two techniques,” Sherer recalled. “You can hit the back of the bottle, with a shoe or something hard that will not break the bottle. The pressure will push the cork out. The other way is to take your thumb or a stick and physically push the cork into the wine.”

Travelwise is a BBC Travel column that goes behind the travel stories to answer common questions, satisfy uncommon curiosities and uncover some of the mystery surrounding travel. If you have a burning travel question, contact Travelwise.