Issue link: http://winesandvines.uberflip.com/i/331901
p r a c t i c a l w i n e r y & v i n e ya r d J U ly 2 0 1 4 65 W I N E M A K I N G & Cie defines tight grain as less than an average of 3 mm per annual growth ring (spring wood + summer wood); larger than this is open grain. Porosity can be misleading When looking closely at the end of a bar- rel stave, one can observe that open grain has fewer vessels (spring wood) per foot, and more fiber and parenchyma (summer wood). Vice-versa, tight grain has a greater proportion of vessels and less fiber material. The fact that tight grain has more vessels means that it contains more void, and is therefore more porous, which goes against a pre-conceived idea that open grain is more porous — it is actually the opposite. This observation is no doubt counter- intuitive for many of us, but it is crucial in properly understanding the differences in oak grain types. It explains why tight grain seems more aromatic: More aromas are released from the vessels, which makes sense as this is where the sap was with minerals, nutrients and sugars. Our observation also explains why open grain feels more tannic: The wine gets more contact with fiber material, as there is a larger proportion of summer wood. With respect to air exchange, several studies have shown it is difficult to draw a conclusion as to whether or not grain tightness influences evaporation loss and oxygenation from the barrel. The higher porosity of tight grain does not appear to allow more air exchange. It would seem that the air permeability of a barrel is more complex, and less influ- enced by grain than by several other wood anatomical factors (such as tylosis filling the wood vessels or orientation of medullary rays on the stave). Over time, compounds are extracted from grain types differently During barrel aging, a complex exchange Microscopic view of structure of French oak grain showing early/spring wood and late/summer wood. PhoTo by TArAnsAud