Tosefta על פסחים 79:13

[Kernels of] wheat or barley that were soaked in water and became leavened -- behold, they are forbidden. Rabbi Yosei says, [kernels of] barley that were soaked in water and burst open, behold, they are forbidden; and [barley soaked] in vinegar, either way (i.e., whether they burst open or not), they are permitted because the vinegar contracts them (Pes. 40a:5).