What is the practical difference between wine that is mevushal and wine that is not? Why would one want one type over another? Which is preferred?
Please send sources.
The difference is that mevushal wine is of lesser quality than non-mevushal wine, and the original decree was only made on non-mevushal wine, which was the common wine at the time.
For this reason, Rav Shmuel Wosner maintains that pasteurizing does not render the wine mevushal, because it doesn’t adversely affect the wine. See Mibeis Levi Vol. 14, p. 55, and Shevet Halevi Vol. 2, no. 51. Only actual boiling renders the wine mevushal.
This is also the opinion of Rav Shlomo Zalman Auerbach (Minchas Shlomo 1:25) Rav Elyashiv (see Shevus Yitzchak, Pesach, siman 16) (both zt”l).
Other authorities however maintain that pasteurization is considered bishul, and there is no need for the adverse effect to be noted.