Most wines are blends, not necessarily of various varietals, but blends of grapes from various regions, vineyards, or sections of vineyards. Often the grapes from these locations are vinified separately and are aged in separate barrels and each batch will develop its own characteristics. This is especially true if native yeasts are used. The various batches may have been made with different yeast strains that produce distinct flavor profiles.
In many wineries, the winemaker will taste these separate batches and decide on a final blend. Her crew will then transfer the proper percentage from each batch to a large tank to be blended before sending to the bottling machine. If executed properly each bottle will contain the same wine.
But that isn’t always how its done. Many winemakers, especially in smaller wineries, will wait until a particular barrel is ready and bottle from that barrel. Then they move on to the next barrel when it is ready, etc. In other wineries, wines may be bottled using fixed percentages of each varietal from various batches without blending in a large tank and without regard for whether exactly the same batch mixture is used for each bottling run. In these cases it’s the same vintage, the same varietals, the same vineyard sources but the bottle variation may be significant.
Does each bottle contain the same wine?
It has also been shown that individual bottles differ in how much oxygen enters the wine at bottling even using the same bottling line on the same day. This too will change the properties of the wine as it absorbs that oxygen.
Even before we get to the issue of storage conditions and differences in how wines develop over time in the bottle, the adage that there are no great wines only great bottles may apply.