Isn't a meritage typically blended after aging and just before bottling?
I am no expert, but seems to me each varietal of the blend might require a different yeast, fermentation techniques, aging, ..etc.
From "What is a Meritage"
Blending for Excellence
Blending is the personal expression of the winemaker’s
vision, a combination of skill and intuition that unites the elements
of the winemaking process to create a work of art. It is the magic that
gifted winemakers use to create wines of intrigue and enchantment.
Blending allows the components of each varietal wine lot to
merge, binding together to form a new expression. Each varietal lot is
kept separate during the vinification and aging process, and evaluated
over time to determine whether a particular facet the winemaker desires
has developed. The final blend is determined shortly before bottling as
the timing of the assemblage depends on the grape varieties selected.
An ample amount of time is allowed for the wine to marry in the bottle
prior to release from the winery, usually two to three years. This
‘blending’ of winemaking expertise and creative intuition produces a
luxury cuvée of opulence and refinement.
Winemakers determine the signature of a blend by determining
which grape variety will dominate. The character or personality of the
finished wine is then refined through a judicial addition of
complementary wines. That is why some blends may contain higher
percentages of Cabernet Sauvignon and others Merlot, than smaller
percentages of Cabernet Franc, Malbec, and Petit Verdot. Insight and a
thorough familiarity of where grapes are sourced and their growing
conditions, is key to blending excellence.