Summer in Michigan Wine Country
“Wine is sunlight held together by water.” - Galileo
Summer in wine country is in full swing, but despite what you might think, that means the grape berries and clusters are just now starting to form into what you ultimately pour into your glass.
There are three key stages of berry development happening during this important part of the life cycle of your favorite vintages:
Cell division & expansion
What started as buds, shoots and flowers back in spring have now become hard little green balls of acid. In this cell division phase, the berry undergoes rapid cell division, accumulates acids (primarily tartaric and malic acids), and ultimately achieves half of its final weight and size.
Phase 2: Seed maturation or “the lag phase”
During this phase the growth of the berry pauses while the energy is primarily being used to create seeds within the berry. During this phase there are chemical signals moving throughout the berry indicating its time for softening and expansion. How long the seed maturation/lag phase lasts is really dependent on the varietal — varieties with long lag phases tend to be later ripening, while varieties with relatively shorter lag phases ripen earlier.
Broadly speaking, whites tend to have shorten maturation phases, which can make them ideal for growing in the midwest where the spring and summers are shorter and the swings in temperature come on fast and furious as you enter the late fall and early spring months.
Phase 3: Grape ripening or Véraison
Véraison is really the moment of ripening brought about by the expression and repression of hundreds of thousands of genes. During this time, berries begin their transformation from hard, green, and bitter, with enamel-stripping acidity, to aromatic, sweet, and beautifully colored. The development of grapes from fertilized flowers to ripened fruit is a complex physical and chemical process.
So what all takes place during this third stage of the ripening process?
Berries soften and skin becomes elastic. Now that the grape berries are fully formed and will survive the elements in the region, they can let their guard down a bit. So during this time, the berries mesocarp (pulp) cell walls loosen giving way to future expansion. As more sugar accumulates in the berry, the hardness of the berry softens, also creating more room and opportunity for expansion.
Berries expand. Once the pulp has softened and the skin of the berry has loosened for expansion, the vine is ready to take in all the water from the soil filling the berry with water. By the time the grapes are ready for harvest, each berry will be 75%-80% water.
Sugar accumulates. Xylem flow slows down and phloem becomes the primary transport highway into the grape during this phase. Xylem is basically the highway from the soil to the grapes. Phloem is basically the highway from the leaves to the grapes. So with less nutrients coming from the soil, and more coming from the sun, there are more amino acids and carbon (in the form of sucrose) available for conversion by the grapes. Sucrose is then broken down and stored as glucose and fructose, or sugar, sweetening up the grape berries. The sugar accumulated during this time determines the resulting alcohol concentration in the wine.
Acid changes. As the Ph increases, acidity decreases. There are two main acids that represent 90% of the acids in grapes that are used for winemaking: tartaric and malic acids. Tartaric acid plays a big role in cell division, expansion and the lag phases of the development but then ceases, malic acid on the other hand is being metabolized all the way through harvest.
Phenolic compounds, including those that cause color change, are formed. These compounds can be found in the skin (Flavonols), seeds (Flavan-3-ols aka tannins) and in the color hues of the grapes (Anthocyanin synthesis). Their presence has a big impact on the ultimate flavor and color of the wine.
Flavor and aroma compounds and precursors develop. Monoterpenes accumulate. Methoxypyrazines decrease. If you’ve ever heard someone say “ah this wine is herbaceous” or alternatively “I’m getting notes of a rose garden” this is influenced by the presence and levels of monoterpenes (coriander seed, rose) and methoxypyrazines (herbaceousness).
As Summer & the ripening process concludes Vinemakers prepare for the harvest.
At the end of the day, summer is a beautiful time on the vineyard, from week to week the grapes go from being babies to full-fledged, big-bodied adults ready to move into the next phase of their lives.
The ultimate goal of the summer season is to ensure the vines and grapes get just enough water, just enough sun and just enough TLC to develop evenly and deliciously - grapes, like people, like a little bit of a challenge, when challenged just enough, they become their best selves.
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