If you read enough about wine you will eventually see terms like “cool climate” and “diurnal temperature range” – the temperature variation in daytime highs and nighttime lows. There will be descriptions of cool ocean breezes making their way through gaps in mountain ranges to blow across warmer vineyards further inland. Fog might be important in some areas as it settles over the vineyards to cool them at night. For cooler regions with shorter ripening seasons, planting in sites to capture the most sunshine becomes important.
We moved to Willamette Valley in time to experience the last few weeks of summer and learned first hand about warm days and cool nights. It does not get very hot here. A few days in the 90’s has people refusing to use their ovens and heading for the cooler coast. Coming from a place where a “cool” summer night means below 100, it was a real shock to comfortably leave the house in shorts and sandals and later wish for socks and a sweater. But these temperatures affect something more important than our wardrobe – they affect our wine.
To understand why, we need a little science. There are two metabolic processes of grapevines to consider – photosynthesis and respiration. You know you kind of remember these from middle school science.
Photosynthesis is when the green parts of plants make sugar. Some of the sugar gets stored in the grapes producing juicy, fruity wines with body and alcohol. Without enough sugar concentration the grapes would have less flavor and richness and may not reach an acceptable alcohol level. Too much sugar and their may be problems with fermentation or the wine could be very “hot” with too much alcohol. Photosynthesis requires warm, sunny days. The Coastal Ranges to the west protect the Willamette Valley from the brunt of the wet foggy influence from the Pacific. Some of this coastal weather, however, makes its way through the mountain crests cooling the area and bringing moisture in the fall. Vines planted on southeast facing hills capture the most ripening sun.
Respiration is when the vine breaks down carbohydrates to use as energy. The important carbohydrate to consider here is malic acid. Warmer temperatures cause increased respiration resulting in more loss of malic acid. In fact respiration doubles for every 18 degree increase in temperature. Remember acid is one of the major components of wine. It is vital to a wine’s ability to either remain fresh or improve with aging in a cellar. It is what makes a white wine taste crisp and refreshing and keeps a tannic red wine from over drying the mouth. It balances sugar so wines don’t taste flabby (think of flat cola) and is key in pairing food and wine.
Therefore the ideal conditions for flavorful wines with balanced natural acidity are warm (not hot) sunny days and cool nights. In some wine regions the addition of sugar to juice (chaptalization) or the addition of acid (acidification) are used to make up for any deficiencies. Likewise in some hot climates where it is allowed, water is added to the juice for dilution. It is preferable for Mother Nature to do her job. The cool Willamette Valley has no need for acidification and while wines are not typically high in alcohol, ~12% can consistently be achieved naturally. So while we may lament the early storing of sundresses and we can no longer “show toes ’till it snows”, we will make up for it by enjoying an excellent glass of well balanced wine – oh and the view. Don’t forget the view.
|Photo by Janis Miglavs for the Willamette Valley Wineries Association|
Look for upcoming articles where we explore the influence of climate on grape selection and how you can use that knowledge to pick the wines you enjoy most.