Thank you Shelley Sharpe for the sole response last week on our Clones topic!
This week: Millerandage
Millerandage – What is it, why does it occur, and how can it affect the final wine? Cite specific examples of grape varieties, where appropriate, that commonly suffer from millerandage.
Millerandage (often colloquially referred to as "hen and chicken") is a poor and irregular fruit set occurring shortly after flowering that results in grape clusters with a mix of normal-sized berries and smaller, seedless berries. This phenomenon has the potential to affect a wine's flavor, development, and quality. However, a small amount of millerandage is not necessarily a bad thing for the quality of a final wine in certain situations. It should be noted that MIllerandage is distinct from the related concept of Coulure (aka "shatter"), which refers to a poor fruit set that results in no fertilization and thus no grape.
Millerandage is most often attributed to poor weather (i.e. cold and/or wet) during the flowering stage of the vine's growth cycle, but nutritional deficiencies and viral infections can also be factors. Some specific nutritional deficiencies include a lack of zinc, carbohydrates, and mineral boron, the latter of which is needed to synthesize growth hormones and facilitate sugar movement in the vine. Insects such as the banded grape bug, lygus bug, and rose chafer can also cause millerandage by feeding on florets and injuring them in the pre-bloom stages. As for the weather, cold temperatures can damage the ovules of flowers before they can be fertilized through the grapevines' self-pollination process whereas rain can wash away pollen from the stigma or dilute the stigmatic fluid before it reaches the ovules.
Since grapes with millerandage will not develop seeds and are much smaller, there is the potential for a much higher juice-to-skin ratio in the affected grapes. This could result in higher (and harsher) acidity or green (and astringent) flavors being added to the wine. To avoid including affected grapes in the final wine, a grower might remove clusters with a high presence of millerandage through "green harvesting" while a winemaker might remove the smaller, seedless grapes on the sorting table just after harvest. Yields will be lower when millerandage is present, which could set the stage for more concentrated fruit if subsequent conditions are favorable.
Grape varieties that commonly suffer from millerandage are those that are naturally prone to uneven ripeness within a cluster, including Sangiovese, Zinfandel, and Gewurztraminer. Because flowering for Merlot is quite staggered, that variety is also at a greater risk of millerandage caused by inclement weather during the fertilization process. Finally, some varieties like Pinot Noir may actually benefit from a higher skin-to-juice ratio caused by a small amount of millerandage, so it is important to note the phenomenon is not exclusively a negative thing.