There are still some great mysteries out there in our world.

For instance:

What exactly was the point of Stonehenge?

Really now, where are Jim Morrison and Elvis Presley hiding out?

And how much do you tip on a bottle of wine?

Ask 10 people you’ll get 10 different answers to all three questions.

But after talking to a bunch of pros, there seems to be some underlying etiquette to the latter.

Look, in general, it takes a lot more work for the restaurant staff to make $1,000 worth of food than it does for the sommelier to go grab a $1,000 bottle of wine out of the cellar, remove the cork and pour it for you.

So why does that require a 20 percent tip? Seems nuts right?

Well, maybe not.

As with all things surrounding tipping, there really is no right answer but here are a few guidelines:

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1. It still comes down to service.

If you asked the sommelier for a nice bottle of white wine and she came back with a bottle of Santa Margherita Pinot Grigio (no offense to Santa Margherita), that’s not service. That’s just lazy.

But if she spent time talking to you, figuring out your tastes and wowed you with a bottle you never had before, then tip her on the wine. So, if you normally give 20 percent, give it on the total bill – food and wine.

2. Consider tipping the sommelier directly.

This is a very common suggestion among wine professionals.

Often, the good sommeliers and wine directors are salaried and a part of management. Therefore, they are not in the waiter tip pool, notes Roberta Morrell, president and CEO of the Morrell Wine Group and the Morrell Wine Bar in New York City.

So you can’t always presume your sommelier is going to get a piece of your 20 percent at the end of the night. And if you’re unsure, ask him.

If the sommelier is not in the waiter pool, and the service warrants it, then absolutely tip him directly.

3. Offer the sommelier a taste.

“When drinking an older or rare wine, I always offer the waiter or sommelier a taste,” says Antonio Galloni, founder of Vinous Media and formerly one of Robert Parker’s lead wine critics for the The Wine Advocate.

That’s because these sommelier don’t often get a chance to taste some of the unopened aged stuff. Offering a sommelier a taste of a rare wine is like offering your kid unlimited servings at the ice cream bar. It also means you just made a friend for life.

And he now may offer you wines aren't even on their main wine list, because you did the right thing, says Galloni.

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4. If you can afford a $500 bottle, you can probably afford to leave a nice tip.

But it doesn’t have to be 20 percent. The consensus out there is that on a $500+ price per bottle, give a round number that is in line with the efforts, not necessarily the price of the wine, says Laura Maniec, master sommelier/CEO of Corkbuzz restaurants and wine studios in NYC and Charlotte.

Morrell says she tips on $250, regardless of the price of the bottle. And that’s completely reasonable within the industry.

And while you don’t have to mortgage your house for the tip, be generous. Your sommlier knows you’re not broke.

So think it through and don’t be afraid to ask questions.

Anyone who has ever served a drink or waited on a table knows all too well that tips mean everything or its Ramen noodles for dinner again.

Or peanut butter and banana sandwiches, which is probably what Elvis is having somewhere right now.

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