The first question that needs to be answered is whether our wines are made differently from our non kosher counterparts? The answer is absolutely not. Our basic ingredient, grapes, are the same the world over. Basic practices in both kosher and non-kosher wineries are the same, the grapes need to be harvested, crushed, fermented, aged, filtered and bottled. Kosher wines use kosher products for these processes whereas non kosher wines do not necessarily.
Wine is made from grape juice to which yeast has been added and allowed to ferment. The resulting wine is cloudy and would be quickly rejected by the average consumer if it was not treated any further. The winemaker has a number of tools for dealing with this, including the use of filtration and the use of additional fining agents.
Fining agents are compounds that are used to help improve the clarity of the wine and also to remove overt bitterness. Commonly used fining agents are a clay-like substance called bentonite, a polymer called PVPP and egg whites (often used in red wines). Some winemakers may use compounds such as isinglass (a fish derivative), casein (a dairy compound) or gelatin (an animal byproduct). These latter two products will severely compromise the kashrut of the wine. Dalton uses only strictly supervised kosher products and certainly no diary products. By the way, kosher wines are not necessarily suitable for vegetarians and vegans.
Secondly, the production of kosher wine must be carried out in a Halachically correct manner (ie. in accordance with Jewish laws): This is more of an issue for wines from Israel as there are many laws pertaining to the upkeep of vineyards such as orla and the sabbatical year (shmitta) and the giving of tithes (maaserot and trumot), which must be respected. For example a vineyard belonging to a Jew in Israel may not be harvested in its first three years (orla), the fruit may only be taken from the fourth year.
Finally and probably the most complex issue is as follows: there is the fear that wine bound for sanctification in a Jewish ceremony will have been used in some non-Jewish rite or ritual beforehand. To this end the Rabbis specify that only observant Jews may be involved in the production of kosher wine thus ensuring the religious integrity of the wine for its use in Jewish ritual.
To further ensure this religious integrity, many wines undergo the mevushal (cooking) process where the wines are flash pasteurised to around 90º C or 200º F. Contrary to popular opinion, you can not make a non-kosher wine kosher by pasteurising it and a kosher wine does not become more kosher after pastuerisation. However, it does make the wine unfit for non-Jewish ritual, and as a result the rabbis permit its use in environments where non-Jews come into contact with kosher wines, such as restaurants and catering halls. Mevushal wines will usually be marked as such.
I will address the question as to whether there is a difference in quality between mevushal and non-mevushal wines in a different post.
For the sake of good order, the supervising Rabbis for Dalton are Rabbi Almishali of Merom Hagalil (our local Rabbi) Rabbi Machpud of the Badatz Yoreh Deyah (He is from Bnei Brak and has been with us since the winery was established), the Union of Orthodox Congregations (OU) we took them because at the time no one in the US knew who Rabbi Machpud was, they do now, and finally Rabbi Mordechai Ungar, he is a really nice Rabbi from New Square New York who brings us added credibility with the ultra orthodox communities, a segment of the market for whom the supervising rabbi is often more important than the contents of the bottle.