Variety - The proper way to say it from the point of view of an english teacher
Varietal - Has become the de-facto technical term in the wine industry and enology educational realms. Like many technical terms there resistence from some people about its use.
Varietal can be used as a noun to describe a kind of wine: those that are made from (or primairly from) a single grape variety. It is a kind of shorthand for “varietal wine.” Example: “Most of our wine store is arranged by region, but you will find varietals such as Chardonnays, Cabs, Syrahs, etc., over there.”
It is always wrong to speak of a “grape varietal.”
Variety = noun
Varietal = adjective. It means of, pertaining to, designating, or characteristic of a variety.
So it’s kind of illiterate to talk about this or that varietal. Kind of like talking about this or that red, or big. You need a noun for the modifier.
What are varieties? They frequently occur in nature and are generally true to type. That means if you plant a seed, the offspring will also have the same characteristics the parents have. That is of course, why people graft apples, pears, etc. If you plant an apple seed from a Macintosh, you don’t get a Macintosh. Same with roses. You get something brand new. So you either propagate by rooting or buy grafting. That means of course, that your apple tree or vine is not descended from mine, making it an offspring; it is in fact the same apple tree or vine, making it a clone.
But don’t stop there.
Cultivar means “cultivated variety”. They are not true to type. So in fact, most grapes are cultivars, not varieties. But people think it sounds cool to talk about a varietal. They’d be totally lost talking about cultivars.
Most wines come from Vitis vinifera. Vitis vinifera includes over 1,000 varieties. The word “variety” indicates that it is a sub-category of a species.
As an example for usage, you can answer the question: “What kind of wine is it?” by saying “It’s a monovarietal wine.” (Remember, what kind of = adjective.)
A nice solution to the problem is mentioned in the discussion following the Oenologic article. Just say cultivar if you want to discuss the type of grape as a noun. Vartietal is an adjective by construction. This keeps the grammarians happy, while eliminating ambiguity since cultivar by default refers to a plant. Variety, which also appeases grammarians, is ambiguous. If you ask “which varieties are used in the production of this wine” you could be asking about oak barrels, yeast strains, etc. I guess cultivar might address different species of oak, but this is a less common query.
The rant on Oenologic - oenoLogic: Varietal is not the spice" onclick="window.open(this.href);return false; - is quite entertaining, and except for one small nit I am happy to pick, correct about variety vs. varietal.
The nit? A varietal (wine) does not have to be made exclusively from a single variety (grape); instead, it can be made principally from one variety (75% or more is a common legal requirement) and, by definition, carries the name of its principal grape on the label.
Your nit is with those who make the rules, as strictly speaking, 75% of one grape with 25% of another does not actually make a varietal wine. It makes a blend, despite what the rulemakers decide to codify.