Grapevine bloom, and the pollination that follows, is one of those amazingly simple but ridiculously complicated things.
First, the basics: Before bloom the only visible part of an individual grape flower is the fused cap of petals known as the calyptra. Once the calyptra is shed, pollen is liberated from the anthers of the stamen. Pollen are shed as the anther ripens
and are primarily
transported by wind, though rarely more than 20 feet from the source. Pollination occurs when pollen lands on the female parts of a flower. Each
pollen grain grows a long tube towards the eggs within the ovary, and sperm cells move down this tube. And you’ve got pollination.
Following fertilization, the fruit begins to form and the flower begins to develop a seed and grape berry to protect the seed. Generally, only around 30% of the flowers on each cluster get fertilized, with the unfertilized flowers eventually falling off the cluster – a term called “shatter.” Climate and the health of the vine play are important factors in the degree of shatter each year.
Grape cluster at about 80% bloom.
Anyway, this is fine and good and educational and all but what I really want to talk about today is the SMELL of bloom. If you’ve ever wandered around or even driven by a vineyard in the month of May you can’t miss it. High tone, sweet and green, not exactly pleasant but not quite obnoxious. And if you think coming up with accurate descriptors of the aroma of certain wines is difficult then take a good strong whiff of a blooming vineyard and tell me what you smell. I’ve heard everything from “herbal shampoo” to “sour Mountain Dew.” Personally, I think of mulched hay soaked in vinegar and honey and topped off with fresh crushed chamomile flowers (organic, of course). But that’s a bit silly, isn’t it? In search of something better (and less silly), I turned to Winemaker and Master Smell Descriptor Mike Brunson. Here’s what he had to say:
Time and time again people ask what I think about a particular smell (being a guy who makes a living from describing smells). For the most part I can come up with something. Then there are certain smells that escape description. Grapevine bloom presses me year after year to come up with something that I can nail down. Bloom is one of the more subtle smells in the vineyard, yet it can be overpowering on the right day. Here’s what I came up with after this season’s bloom:
Grapevine Bloom…
1. A soft entry, grapevine bloom quickly turns into cheap perfume with a distinct spicy jasmine/death smell finish. It is fairly short lived. In other words, bloom doesn’t hang around like cheap perfume often does.
2. With a bit of dried flowers (the kind you normally find in potpourri), Grapevine bloom delivers the soft smelling punch that stymies the senses with it’s small power. It smells like cotton candy that somebody sprayed cheap perfume on.
3. Perfume, apple blossom and light bee’s wax all come together to showcase the vineyard’s potential for the season.
It’s a one of a kind smell that happens only once each year.
So there you have it. I guess. Maybe it’s like trying to describe the smell of your favorite childhood meal – it just can’t be done. Or maybe, just maybe, we can turn to science for clues. With a bit of digging through the latest research journals I learned the source of the smell of bloom: Valencene synthase (VvValCS) enzyme activity, which produce major sesquiterpene volatiles.
O.K… That didn’t help much.
I also discovered that the unique aroma of the grape flower comes from the pollen, unlike other flowers such as roses whose scent arises from their petals.
That’s kinda cool.
But, really, why do grape flowers smell at all? It’s believed that flower fragrance developed evolutionarily to attract pollinators. But grapes are largely self-pollinated. It could be that the aroma serves more as a defense mechanism to protect their male reproductive tissues from predatory insects. Or it could be some other reason. Or it could be that the odor has no particular function.
Maybe it just is.
Tony
