Harvest early or tough out a week of rain?

[BigH]

My Petite Pearl vines are a touch shy of ripeness, but we are facing a week of solid rain. Curious if fellow growers would harvest early or try to weather the storm

Variety : Petite Pearl
Sample date: 9/1/18
Brix: 22
pH: 3.15
GDD: 2892 since Mar 1

Last year's harvest on 9/12 produced a crush that measured 24.8 brix and a pH of 3.29 and was picked with the GDD at 2970. We are 150 heat units ahead of last year, but bud break was a couple weeks later.

The recommended harvest parameters are sugar at 24.5 and pH around 3.4. If it matters any, Petite Pearl is supposed to have tough skins and should not suffer berry splitting problems. However, it does form a pretty tight cluster.

H

 

[salcoco]

the risk you take is that the brix will go down.

 

[Masbustelo]

How about pick and use a yeast that metabolizes the malic acid like 71B, Andante/Avante or Maurivin B. You should end up with a surprisingly acceptable Ph , particularily with the Maurivin B and probably Avante as well. You can add some sugar if you wanted to, at 22 Brix your pretty good.

 

[ibglowin]

My vote is to let them hang. At that pH and Brix you have time on your side to let things dry out again. Brix will go back up shortly and probably go higher yet. Longer hang times are always better in my book and make a better wine. As long as you have heat forecast ahead that is what I would do.

 

[CK55]

I would harvest.

 

[balatonwine]

This is actually not an easy question to answer. Other than ... It depends.

I have spent nearly two decades trying to figure out the ideal time to harvest. And long periods of rain really throws a monkey wrench into that decision making process. Some times I get it right. Some times I get it wrong. Last year I harvested before a long rain event, and my neighbor did not. This year, I am in day 2 of 5 days or rain. My neighbor harvested before it, I did not.

Why did I harvest last year and not this year before the rain? In the end, it comes down to the same thing: finding balance.

What I mean by that is my grapes were in balance last year and could be harvested before the rain. This year they were not. So I am letting them hang. I may get some Botrytis, but as long as the weather stays dry after this rain event long enough to harvest (so the noble rot does not go to gray rot), that will not be really a problem (in fact, some noble rot will increase brix).

Your grapes I would say are not in balance. Even by the simple "when to harvest" formula of ph squared times brix, you have a value of 218. For reds, that should be around 260 before you harvest. See, for example:

https://en.wikipedia.org/wiki/Ripeness_in_viticulture#Balancing_sugar,_acidity_and_pH

A week of rain may seem like a lot, but what is more important is what is the long term weather forecast after that? If it will be dry, I would not harvest now. I would not worry too much about things like Botrytis. If you knew the weather was coming, you could have sprayed with potassium bicarbonate, such as Amricarb, to help prevent it. Or just accept if you get a little as long if it stays as "noble rot", which really does not do that much damage as long as it does not progress to gray rot which probably will form if the rain continues without much of any dry days in between.

And again, all above is just a small sliver of the decision making process. A lot of the final decision will only get better with time and experience. Which means, like I did, you may make the wrong call some years as part of the learning process.

 

[KevinL]

I'm staring the same week of rain down. For what it's worth I'm letting mine hang.

 

[BigH]

How about pick and use a yeast that metabolizes the malic acid like 71B, Andante/Avante or Maurivin B. You should end up with a surprisingly acceptable Ph , particularily with the Maurivin B and probably Avante as well.

This would have been the game plan if I had harvested. One piece of information I am still trying to find is how much those yeasts contribute to the ABV when they metabolize the malic acid. That metabolism is worth some equivalent sugar addition to a non metabolizing yeast strain. How many brix is that equivalent sugar addition?

71B * 22.5 brix == RC212 * (22.5 + X brix) << with respect to alcohol only

Solve for X. I know it is going to depend on how much malic acid is present and probably some other factors. I would be happy with a ballpark number.

H

 

[BigH]

Your grapes I would say are not in balance.

Ultimately, I did decide to let them hang. I can't say that it was brix * ph^2 that convinced me. It was more a culmination of these factors

* Petite Pearl is supposed to be my late season, low acid grape, vinifera like grape.
* Skins are supposed to be tough and not prone to splitting
* I was faced with the same decision with Frontenac, which could have used another 1/2 week in sunny weather. I plucked the Frontenac and didn't have a lot of excess capacity to deal with the PP before the rain
* Frontenac seemed closer to ideal harvest than my Petite Pearl did, and less likely to weather the rain
* I want to see what happens.

I harvested Frontenac on Thursday, threw it in the fridge, and crushed it Friday. I did have a window of sunny weather on Saturday to grab the Petite Pearl after receiving a half inch of rain Friday night. I decided to let it hang. Was really regretting that decision by Sunday. But it is only 9 vines. Would hate to lose what I view as my best grape, but I need to learn what it can take as well. Will chalk the failure up as learning if it does't pan out.

Thanks to all who answered. I welcome more suggestions even though the decision has been made (actually, it was made by the time I posted)

H

 

[cmason1957]

This would have been the game plan if I had harvested. One piece of information I am still trying to find is how much those yeasts contribute to the ABV when they metabolize the malic acid. That metabolism is worth some equivalent sugar addition to a non metabolizing yeast strain. How many brix is that equivalent sugar addition?

71B * 22.5 brix == RC212 * (22.5 + X brix) << with respect to alcohol only

Solve for X. I know it is going to depend on how much malic acid is present and probably some other factors. I would be happy with a ballpark number.

H

I'm not sure I would agree that metabolizing some of the malic acid does much, if anything to Abv level. I don't see why it would. Acid isn't sugar, it doesn't get metabolized to sugar. If you have a recency that indicates otherwise, please share.

 

[Johnd]

I'm not sure I would agree that metabolizing some of the malic acid does much, if anything to Abv level. I don't see why it would. Acid isn't sugar, it doesn't get metabolized to sugar. If you have a recency that indicates otherwise, please share.

I recall that someone recently posted that 71B converted malic acid to alcohol, but I’ve not taken the time to research the issue.

 

[cmason1957]

Perhaps 71B has a slightly higher conversion factor than some other yeasts and that is what was meant. I don't think it converts malic acid to sugars and increases the alcohol due to that conversion.

 

[BigH]

Perhaps 71B has a slightly higher conversion factor than some other yeasts and that is what was meant. I don't think it converts malic acid to sugars and increases the alcohol due to that conversion.

Yeasts like 71B can metabolize malic acid into ethanol (more so than typical yeast strains anyway). The process is known as maloalcoholic fermentation. I have also seen it referred to as "malo-ethanolic deacidification". I don't know what intermediate compounds are involved, but both malic acid (C4H6O5) and ethanol (C2H6O) are simpler compounds than sugars like glucose or fructose, so the pathway seems unlikely to involve sugar as an intermediate. I found one article abstract that mentioned acetaldehyde (C2H4O) as an intermediate, but did not read the full article.

My point was this. Suppose 71B and yeast A have the same ability to convert sugar to ethanol. Suppose I turn both of them loose on separate batches of the same high acid must with a brix that is well within the alcohol tolerance of both strains. 71B should produce a wine with a higher ABV than yeast A. I would have to chaptalize the must for yeast A to get the same ABV. What is that effective chaptalization amount? Is it insignificant? I have yet to find an article that quantifies this.

Here is an interesting quote from an article I was reading today

How can I decrease acidity levels
...

• Carry out primary fermentation with a malic acid-metabolizing yeast strain, conducting the process of maloalcoholic fermentation. Some strains of Saccharomyces cerevisiae (e.g., Lalvin 71B or Lalvin AC) can metabolize 20 – 40% of the malic acid present in a must, producing alcohol instead of lactic acid. These strains reduce the amount of malic acid available for MLF, and lowering the risk of getting too much “mouth feel improvement.” These strains offer reduced risk of losing varietal character.

H

 

[sour_grapes]

I have not done the math, but could be convinced to. But, I really don't think it is worth your while. Total acid contents are in the range of, say, 7 g/L. This is also known as 0.7% (by weight.). Malic is not the dominant acid. Let's wildly guess it is 40% of the acid, so, ~0.3 weight%. If 40% of this is converted to ethanol (as your source says), it would contribute ~0.12 weight%, or ~0.1% ABV. Obviously, this is within the error bars. I wouldn't overthink it, personally.

 

[balatonwine]

Ultimately, I did decide to let them hang. I can't say that it was brix * ph^2 that convinced me. It was more a culmination of these factors

Good call.

Singular issues like brix * ph^2 are simply another arrow in your quiver. Final decisions are always best made on a preponderance of many factors.

 

[balatonwine]

I have not done the math, but could be convinced to. But, I really don't think it is worth your while. Total acid contents are in the range of, say, 7 g/L. This is also known as 0.7% (by weight.). Malic is not the dominant acid. Let's wildly guess it is 40% of the acid, so, ~0.3 weight%. If 40% of this is converted to ethanol (as your source says), it would contribute ~0.12 weight%, or ~0.1% ABV. Obviously, this is within the error bars. I wouldn't overthink it, personally.

Numerically I agree.

Mathematically I agree.

But.... on any distribution of tasters.... what is your target audience? Maybe some can detect the difference of what comes from where. And maybe you are interested in catering to those.

Doubt it? Well, after all, Fisher developed his exact test, and wrote a famous paper about it, because Muriel Bristol said she could detect if tea was added to milk or vise-versa (according to the test, despite "common sense", she could).

https://en.wikipedia.org/wiki/Lady_tasting_tea

“There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy.” ~ Hamlet. Act 1, scene 5.

 

[BigH]

Well, we have finally emerged on the back side of an incredibly slow moving, rain laden, stationary front. The last 3 days have been sunny and the rest of the week looks sunny and hot. Sampled yesterday and had brix at 23.8 and pH at 3.23. I think I am going to pluck them tomorrow or Wed morning. They are looking pretty tough after the rain, and keeping the pests at bay is becoming a challenge. brix * pH^2 now stands at 248 vs 221 before. I have a hunch that my harvest pH will come in around 3.3 (berry sampling bias + 3 more days of nice sun)

H

 

[BigH]

Final parameters

Harvest date : 9/12/18
Harvest GDD : 3127
Harvest Sample: 23.5 brix, 3.3 pH
Must sample before fermentation : 23.2 brix (hydrometer), 3.35 pH

Could have waited a bit for little better harvest params, but I was seeing a lot of bug damage, particularly sap beetles (aka picnic bugs). Most insecticides don't take them out. Lost 10-15% of the crop due to damage. Late season protection of the crop is still something I am figuring out.

Overall, I am happy with the decision to wait. The wine that is through press and into MLF. Everything is looking good at the moment.

H

 

[JimInNJ]

I identified sap beetles damaging my syrah this year and realized that they were probably also responsible for mystery damage last year. They don't appear to have bothered my more open clustered varieties.

They are apparently considered a "nuisence" pest, so not usually listed on pesticide labels and not much discussed by the university extensions.

I used Cypermethrin mixed with pyrethrins figuring that might help flush them out. Seemed to work.