(Wine-Searcher) - As Passover approaches, kosher wine is gearing up for a healthy spike in sales.

So what is the big deal about kosher wines?

It's difficult to get an idea of the size of the kosher market worldwide but it is  "shockingly large", says blogger David Raccah of Kosher Wine Musings. "France is $65 million alone, Israel makes 36m bottles, the US 1m bottles. Then there is Italy, Chile, Spain, Argentina…" And it's getting bigger. The wine importer Kedem reckons the US is growing at a rate of eight percent a year. From the astonishing rise of Bartenura Moscato – which now sells 3m bottles a year – to the kosher versions of Bordeaux cru classés, kosher wine is everywhere. One of the reasons for the rise, those who study the kosher market say, is that less than a quarter of those that consume kosher wines are actually Jews. You could be drinking a kosher wine without even knowing it.

Is kosher wine any good?

In the olden days, it used to have a terrible reputation as over-sweet, or with all character boiled out. Now that serious winemakers are in on the act, with big investment and modern winemaking skills, any well-made kosher wine will be at least as good as or better than its non-kosher counterpart. Former journalist Jeff Morgan of California's Covenant Wines says the kosher wines he tasted in the 1990s were so good he was inspired to start his own winery. The wine in question was a red from Israel's Domaine Castel. "It was delicious. It helped me realize that a good kosher wine could be as good as any good non-kosher wine." He and Leslie Rudd (of Napa's Rudd Estate) started Covenant the following year.

What's the origin of kosher?

Those who drafted the Jewish laws decided there had to be a way of ensuring a wine had not been used for idolatrous purposes – by pagan worshippers placating their own gods with offerings, for example. Making sure only a Sabbath-observant Jew had touched the wine was one way of doing this.

Is kosher wine made differently to other wine?

Yes and no. In order to be kosher, the making of the wine must be supervised by a Sabbath-observant Jew or rabbi. The processes are the same – although all ingredients used, from yeast to egg-white finings – must be kosher as well.

But what about mevushal – doesn't that entail boiling the wine?

For those who want to be doubly sure their wine is kosher, the idea of mevushal came about. Mevushal literally means "cooked". In the past the wines would be boiled but now they are flash pasteurized, which is somewhat gentler on the wine. A mevushal wine remains kosher even if touched by a gentile. As with everything, there are different standards depending on who is certifying the wine. Some rabbis think 180°F is hot enough. Others want up to 195°F. Those supplying kosher wines to the US may use mevushal as insurance. "Servers in restaurants won't necessarily be observant," Hélène Combabessouse of Bordeaux's Barons Edmond and Benjamin de Rothschild told Wine Searcher.

If a gentile touches a normal kosher bottle, does it become non-kosher?

Only an open bottle. That's why at kosher tastings, all the servers behind the tables are observant Jews (often students drafted in for the purpose).

What about in the vineyard – do pickers have to be observant?

No – grapes in their natural state are automatically kosher. It's when you start doing things to them in the winery (from the crushing phase on) that they become non-kosher.