Grape juice and wine carry requirements that nothing else in kashrus does. A wine can be made from nothing but grapes, with no additive of any kind, and still not be kosher. Understanding why makes the rest of the category make sense.
Two different prohibitions
Yayin nesech is wine used by a non-Jew for idolatrous purposes. That is the original and more severe category.
Stam yeinam is ordinary wine handled by a non-Jew, with no such intention at all. This is the category that applies in practice today, and according to many poskim the Sages prohibited it in order to discourage intermarriage — wine being what people share socially.
Note what that means: the reason is social, not about the wine's composition. Nothing has gone into it. This is why the rules look strange if you approach them expecting an ingredient question.
The two categories largely track one another in their practical consequences, with some differences — notably around deriving benefit rather than drinking.
What it covers
The requirement extends beyond a bottle of wine to grape products generally — grape juice, concentrate, wine vinegar, and ingredients derived from them. This is why grape derivatives are one of the standard flags in any ingredient review, and why they catch out manufacturers who were only thinking about animal products.
Cooked wine — mevushal — is treated differently and much more leniently, which is why so much kosher wine sold for general use is mevushal. What qualifies, and what your household relies on, is a question for your rav.
Vessels absorb it
Here is where it reaches further than people expect. When a non-kosher liquid sits in a vessel for twenty-four hours, the walls absorb from it through kavush — soaking. A kosher liquid subsequently resting in that vessel for twenty-four hours absorbs what the walls took in.
So a barrel is not neutral. It carries what it held.
The Rema rules that kosher wine stored in a barrel previously used for forbidden wine becomes forbidden, unless the volume is sixty times greater.
When does grape juice become "wine"?
The prohibition attaches to wine, so the boundary matters — and it is drawn in two places that surprise people.
At the start: unripe grapes already count. Juice pressed from grapes that have not ripened is called wine and is subject to a non-Jew's handling, even though it is still very sour. The reason given is refreshingly candid: we are not expert in judging until what point a grape is still unripe, so the line cannot be relied on. Where such juice was put into food and its taste changed, it is no longer subject to it — and all the more so where it was cooked.
At the end: vinegar is outside it. Full wine vinegar was not used for libation, so it is not forbidden by a non-Jew's handling. The test given is physical: throw it on the floor, and if it bubbles and seethes strongly, it is full vinegar.
But the timing is everything, and this is the trap. If the non-Jew touched it after it had turned to vinegar — permitted. If he touched it before, and it turned to vinegar afterwards, it stays forbidden. Becoming vinegar does not undo what already happened, in exactly the way that distilling it does not.
Diluted wine
Wine mixed with water is nullified at six parts water to one of wine, and at that dilution is not forbidden by a non-Jew's handling. Below that ratio it is forbidden.
Two refinements worth noting. Some hold that as long as it still tastes of wine it remains subject to handling. And there is a neat rule of thumb offered: anything over which one would not say borei pri hagafen is not forbidden by a non-Jew's handling.
That rule of thumb is not quite a rule. For the bracha, a majority of water is already enough to make it shehakol; for the handling prohibition, the measure is six parts. The two thresholds sit at different places.
The dilution allowance is also specific to water. Wine mixed into other wine, or into a dish that it improves, is a different question — there the requirement is sixty.
Before the wine is drawn off
There is a stage in winemaking where the rule has not yet engaged: as long as the wine has not been separated from the skins and pips, it is not forbidden. This is hamshacha, the drawing off.
It explains something about how wineries are supervised — the point at which the handling restrictions bite is a specific moment in the process, not the whole of it.
Wine that has set solid
Congealed wine is not subject to a non-Jew's handling, and neither is his touching earthenware that has wine absorbed in it.
Once again, sequence decides it. Where a non-Jew touched the wine and it congealed afterwards, the prohibition does not lapse. And where congealed wine is designated for drinking, it is subject to handling again.
Raisin wine
This is the case most worth knowing, because many households have used it without realising what it is.
Take raisins moist enough that pressing them would yield their juice. Crush them, soak them in water for the purpose of drinking rather than to eat the raisins, leave them three days fermenting, and pour the liquid off into another vessel. That liquid is full wine.
Which means it takes borei pri hagafen and the after-bracha of me'ein shalosh, and it serves wherever a cup of wine is required — kiddush included.
The conditions are specific:
- The raisins must be more than a sixth relative to the water, measured as they were when moist, before drying.
- It must be made by soaking. Cooking raisins in water does not produce wine.
- Do not add so much water that the swollen raisins are only one in six — at that point a bracha of hagafen would be said in vain. Some hold the limit is tighter still, and that with our weaker wines one should not add more water than the volume of the swollen raisins.
- Where the raisins were soaked or cooked intending to eat them too, the bracha on the liquid is doubtful.
And so raisin wine is subject to handling
This is the practical consequence, and it is easy to miss: since the liquid is wine, a non-Jew's handling forbids it — and that includes the soaking water itself.
The Ben Ish Chai states it from lived practice. In his city raisins were soaked in hot water on erev Shabbos precisely so that kiddush could be made on the raisin water — and he warns that it must be guarded from a non-Jew's touch, because such a touch forbids it.
The hamshacha rule applies here too, and he describes it concretely: in Baghdad raisins were soaked in a barrel for twenty days or more, turned and mixed by hand daily until they became wine. As long as the wine had not been drawn off from the raisins, a non-Jew's touch did not forbid it. Some are stringent with raisin wine even before it is drawn off, but many disagree, and the ruling follows those who do.
Raisins cooked in water are not subject to yayin nesech at all, on the law of cooked wine.
The rule that permits a great deal
And then a striking exception. Water, beer, or any liquid other than wine stored in such a barrel is permitted — provided the barrel is clean.
The source is a case in the Gemara where storing beer in a barrel that had held forbidden wine was allowed. The poskim explain why: wine ruins the flavour of other liquids. It is nosen ta'am l'pgam — taste that spoils rather than improves — and taste that spoils does not prohibit.
That single principle carries much of what follows for spirits. See whisky and sherry casks, where it is tested at its limit.