A Wellington Wine Blog (of sorts) Part 4

What I Would be Doing This Month if I Hadn’t Retired

September
About three weeks ago the local newspapers ran stories (as they do every year) about the first winegrape harvest of the vintage, for sparkling wine, harvested at much lower sugar levels than grapes for still (non-sparkling) wine. I commented that harvest was starting a week or more later than the average date, and my wife was surprised. She said that didn’t make sense because it’s been a hot summer – therefore shouldn’t the grapes ripen sooner? Grapevines are certainly dependent on heat; it is the dominant variable in the rate of sugar production, which is responsible for vine growth and grape ripening. So how could a hot summer result in a late year?
Photosynthesis (sugar production) in grapevines is insignificant below 50°F, peaks in the low to mid 90’s, then drops rapidly, approaching zero at around 105°. Grapevines don’t produce a lot more sugar at 95° than they do at 80°, so summer weather doesn’t have as profound an effect on the rate of ripening as one might intuit. This is why we can make rather accurate projections of harvest dates at bloomtime, three months in advance. Quite the opposite applies with spring weather; there is a huge difference in photosynthesis rates between 55° and 70°, and the interval between budbreak and bloom can vary wildly. Cool weather from March through mid-May of this year is the reason for the late bloom and late start of harvest.
If our crush hadn’t started by now we would have been continuing with prep – washing and testing equipment, ordering and receiving supplies. Whether or not crush had started I would have been spending a lot of time in our vineyard as well as all the vineyards from which we purchased fruit. Water status, and therefore irrigation timing and amounts, becomes very important now, and it’s also a last chance to thin or make other adjustments. IMHO the most important single decision in a wine’s life is the timing of harvest, ideally a decision based as much information as possible, including rates of ripening progress which can only be discerned by regular vineyard visits. Testing for sugar and pH provides useful information, but there is so much more that can only be known through regular trips through the rows. The things I noted when checking vineyards pre-harvest included crop load, leaf and shoot tip status, stem lignification, skin texture and how easily berries pull from the stem, seed maturity, color release from grape skin cells, flavor and astringency (a subjective measure of tannin polymerization). Observing the rate of change of these factors is useful in projecting and ultimately deciding harvest dates. Most wineries reach full capacity at least once each harvest, and good scheduling is critical to both smooth operation and wine quality. I was fortunate that I never had to delay a harvest more than two days from what I thought was the ideal date; I’ve heard many stories of growers being put on hold for two or three weeks after their grapes were ready because of lack of tank space.
The sum of information and understanding gleaned through multiple vineyard inspections also provides information that will be useful in decision making once the grapes are in the winery. More on that in a couple of weeks; I’ll be posting “October” prematurely because I’ll be in Spain (for the first time!) almost all month.