When discussing a thief’s obligation to return a stolen object, if he owes less than a peruta, the obligation of return, he does not need to chase down the owner to return it to him. The issue of partial payment is discussed by Rava, which leads the Gemara to bring a number of cases where Rava takes positions on similar issues.
One such case that is discussed by the Gemara is a havit – a jug or barrel – that has a hole in it, but the hole was closed up by shemarim – sediment. In that situation, the havit is still considered to be complete with regard to the laws of ritual purity.
Rashi explains the case to be one where the havit was an earthenware vessel covering a chimney or other opening in a house, thus protecting objects in the connecting attic from becoming tameh. This would only work if the utensil was whole. Rabbeinu Ḥananel and other rishonim suggest that the case is one of a tzamid patil – a tight-fitting cover on an earthenware vessel, which protects the contents of the vessel from tum’ah.
The sediment that closed up the hole or crack in the vessel is the product of the fermentation process in wine. During fermentation, yeast interact with natural sugars in the grape juice producing ethyl alcohol, and carbon dioxide. As the yeast grow and develop during this process, they become stuck to each other and produce clumps that are often heavier than the wine, which causes them to sink to the bottom of the barrel. These may harden and create a layer of impermeable material. Since the development of the sediment is encouraged by the exposure to air, it is not surprising to find a large amount of sediment near a crack in the barrel, something that will likely close the hole.