58 Knowing When To Pick Your Grapes
Description
This article is from the WineMaking FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions by others.
58 Knowing When To Pick Your Grapes
{Is there any way of determining the right time to harvest grapes save
purchasing the commerical product telling the sugar content? I don't
have that many vines to warrant the expense.}
A couple of interesting suggestions have been made by Cox in 'From
Vines to Wines.'
One is to measure the ratio of Brix to TA. Harvest when the ratio is
between 30:1 and 35:1, and don't go beyond 35:1 unless you're making
botrytized or sweet dessert wine. His caveat: if you are living in a
cold region where high acidity is a problem, you may not get to 30:1.
For example, the grapes may only get to 25:1 and stay there. He
suggests suggests to check the pH. If it's approaching 3.2 to 3.3 for
whites and 3.4 to 3.5 for reds, harvest, no matter what the Brix and TA
are doing. The pH gives a check against total reliance on the Brix:TA
ratio.
The other, and Cox says this is more accurate, is to multiply pH by
itself, and then multiply that by Brix. Harvest whites when the number
gets as close as possible to 200, and reds when the number approaches
260. And try to keep pH below 3.3 for whites and 3.5 for reds. If it
goes higher than those, harvest.
He summarizes: "Keep measuring. Don't let the pH go above 3.3 with
whites or 3.5 with reds. Harvest when the Brix:TA ratio is as close as
posible to 30:1-35:1, and when Brix times pH squared is as close as
possible to 200 for whites and 260 for reds."
One other suggestion is that the winemaker can consider the prospective
alcohol content of the finished product. If he decides, for example,
that his white table wine tastes best with an alcohol content of 11.2%,
he would pick at 20 Brix, because he knows that the finished product
will have approximately 56 percent by volume alcohol to the original
sugars (i.e., 20 Brix times 56% equals 11.2%).
A theoretical "ideal" red grape: 22.5 Brix, .7 TA and pH 3.4. Ratio is
32.14; Brix(pH2) is 260.1.
T51. WILD YEASTS
Some people try to use the yeasts/bacteria that come on the grapeskins
as the primary fermentation organisms. The most important thing to
realize is that with the "natural" method you're not fermenting the
sugars and digestable acids with monocultures but with a broad
polyculture of various yeasts and bacteria. It seems that this
polyculture is as much a part of the "terroir" of the site as the soil,
exposure, etc.
It is suggested that you do the following:
1. Use grapes that are in good condition (little mould.)
2. Make sure pH is correct to avoid over population of bacteria.
3. Cap the must with CO2 after crush until the ferment is producing
enough CO2 on its own to protect from oxygen contact.
4. Monitor ferment closely.
5. I like to ferment reds hot (85 - 90 F).
5. Cap with CO2 at the end of ferment until you press.
Many find that the polyculture and the longer, drawn out ferment will
yield a more complex wine. A good experiment would be to split your
grapes and ferment each half with each method and see what you like
best. You may or may not enjoy the "complexity" that results from the
"natural" method. Practical Vineyard and Winery has a bunch of detailed
articles about this subject.
Others feel that the low cost of a packet of yeast -- about USD$1.00 at
most -- and some sulphite at the beginning is a good investment in
making sure that you avoid potential problems in lost wines to
unpredictable polycultures. A good yeast to use is a "Killer Yeast"
such as Lalvin K1-1117.
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