The Gemara (A.Z. 55b) says that wine becomes susceptible to mageh akum only after hamshacha. Before this point mageh akum will not make this wine assur. Hamshacha takes place when some amount of clear juice is separated from the peels and pits. Even if only a tiny amount of juice is separated, all the remaining juice that is still mixed with the peels and pits is now susceptible to mageh akum. This is brought in Shulchan Aruch (Y.D. 123:17). Even if we are uncertain as to whether hamshacha took place, Shulchan Aruch (Y.D. 123:19) rules that we must be machmir and assur the wine. Therefore, a full barrel of crushed grapes although it appears that hamshacha did not take place, if left in the possession of a non-Jew, becomes assur. We must suspect that some clear juice was removed by the non-Jew, thus invalidating all the remaining wine.
This has direct implications for grape purée. Although, grape purée or grape purée concentrate contains all the pulp and solids and there is no necessity for hamshacha, still it is only kosher if made with the constant supervision of a mashgiach, because of concern that juice samples might have been taken, which would constitute hamshacha. Grape purée concentrate is often sold at a level of 52 Brix. This means it is 3.8 times more concentrated than single strength purée (16 Brix). It will take 22.8 parts water to be mivatel one part of 52 Brix grape purée.
Raisin purée on the other hand, can be made without producing any juice. In the cases we have examined, though a small amount of water is added to a raisin mush, the water is immediately absorbed. This type of production does not require hashgacha temidis, because there is no juice produced. At all times it remains a thick raisin paste like purée. Nevertheless, it is possible that other methods for forming raisin purée exist and therefore non-certified raisin purée is not acceptable. Of course plain raisin juice requires all the chumros of grape juice or wine production
Although stam yayin is batel in 6 parts water, it is questionable if this applies to stam yayin vinegar as well. Although, in general this does not make much of a נפקא מינא, since vinegar is not commonly added to drinks, and in ochlim, we certainly require bitul b’shishim and perhaps even more if we consider vinegar an avida l’taama. However, one very practical נפקא מינא is the return condensate from steam used to heat wine vinegar. If the reason that 6 parts water is adequate to be mivatel grape juice is because we know that this quantity of water is pogem grape juice1, then unless we have a proof that this quantity of water is pogem vinegar, we cannot apply this leniency to wine vinegar. However, Igros Moshe (Y.D. I:62) writes that the correct explanation for why 6 parts water is mivatel wine is not because the water is pogem the wine, but rather because wine loses its identity when it becomes diluted, and all that remains is a קיוהא בעלמא (sourness). Rav Belsky said that this argument can be applied to wine vinegar as well, and we can therefore be maikel regarding return condensate from wine vinegar. If actual stam yayin vinegar is mixed into a beverage (e.g. tomato juice), the office should be consulted for a psak.
Wine alcohol (ethanol)
If stam yayin is kavush in a barrel, only a kdei klipa of the barrel becomes assur. The Noda B’Yehuda (Y.D. II:67) writes that wine alcohol because it is charif will assur the entire thickness of the barrel. A similar sevarah is brought by the Ikrei Dinim18:17 regarding wine vinegar. He writes in the name of the Maharam Provintzali that since wine vinegar is a davar charif, a barrel that held stam yayin vinegar requires hagalah. Because vinegar is considered rosai’ach, it does not suffice to kasher with milui v’irui. Rav Baruch Frankel, in his Hagaos on the Noda B’Yehuda, disagrees. He says that in reality stam yayin too affects the entire thickness of the barrel, yet Chazal allowed a special kula and only required kashering a kdei klipa. Since wine alcohol and wine vinegar are merely alternative forms of stam yayin, we need not be more machmir. Rav Belsky has ruled that in cases where there are other tzdadim we can be maikel. For example, a large vinegar tank that is machzik shishim, can be kashered with milui v’irui or irui kli rishon, if hagalah is not possible.
1 Mateh Yonasan on Y.D. 114:4