Mold damaged grapes: crush or toss?

[nanobrau]

I’m in the California Bay Area. This years heavier than normal rains brought a lot of mold on plants. My gewurstraminer produced well, but got attacked by powdery mildew. This is the first time I’ve encountered it to this degree, so I’m wondering if it’s even worth making wine from the mold-damaged grapes? Some examples:

A - little to no damage:


B - over 50% of berries are damaged:


C - Nearly 100% of berries damaged:


This is all for home winemaking, so I’m hesitant to throw much away unless it will produce truly awful wine. Should I just throw them all together and sulfite well? Ferment A, B, and C groups separately? Just toss clusters like C? All thoughts appreciated.

 

[VinesnBines]

If you have enough grapes and capacity, I say ferment A, B and C separately. Give batches B and C an extra heavy does of Kmeta at crush/press and let a day or so pass before pitching your yeast. Crush A first then B and C to keep the contamination away from A.

Last year I had some dreadful looking Cayuga with sour rot. I tried to sort the grapes but finally crushed, added a heavy does of Kmeta and prayed. It turned out great. The grapes looked so bad that I would not have taken them if someone had offered for free. Since I spent so much time and energy growing them, I didn't have the heart to toss them.

What can you lose by trying?

Others will tell you to toss B and C. Follow your instincts.

 

[NoQuarter]

It is said that powdery mildew on less than 5% of grapes with taint the wine and produce off flavors ..
Possibly you could pick through and get enough unaffected grapes to make a smaller batch.
I have been spraying every 10 days with 40/60 milk to water. Works very well in my high heat and humid area..and I get milk for free.
There are certainly chemicals folks use as well

 

[Rice_Guy]

Powdery mildew is not known to be a human poisoning agent. Your main risk is off flavors.

 

[winemaker81]

If you have enough grapes and capacity, I say ferment A, B and C separately. Give batches B and C an extra heavy does of Kmeta at crush/press and let a day or so pass before pitching your yeast. Crush A first then B and C to keep the contamination away from A.

If it were me, this is what I'd do. The worst case scenario is that batches B & C get dumped, and time/effort was wasted.

 

[ChuckD]

I would probably sort and ferment A and B and toss group C. But once sorted it’s not a lot of extra work to ferment them all.

 

[Greg Corey]

When I make cider from random neighborhood trees that haven't been sprayed with pesticide (all Apples will have coddling moth damage in Utah - and most of North America AFAIK), I basically do A, B, C above with A being my own apples that I take care of and B and C being whatever I get from neighbors. Some mold will grow on the inside of the apple where there was damage and I used to painstakingly cut out the cores of 100lbs of apples to avoid taint. No More! I generally ferment without any meta - both grapes and apples - but for those apples I do a large dose up front and while it's not as clean a flavor as my well maintained trees, they don't have a bad flavor either. Just more rustic tasting to me. I say go for it. My experience has been satisfying.

 

[Hazelemere]

throw it out

 

[Shurt1073]

What are past practices? This is new to you but can't be the first time ever?

Best of luck and hope its not a total loss. Positive vibes your way!

 

[CDrew]

So, I don't know, but that doesn't prevent me from giving advice! I would do a grape taste test. If the grapes taste OK, the wine will likely taste OK. You have nothing but some yeast and some time to loose and it might work out. Taste through the grapes and if you find that A and B taste good and C does not, sort out the Cs. But I'd likely ferment anyway and you'll know if it's worthy of further processing in about 10 days.

 

[Obbnw]

The last time I had powdery mildew damage is was in the A to B range. Red wine grapes. Most of them split and dried up before fully ripening. I did ferment the ones that made it and it seemed OK but I ended up tossing it anyway. It was only about 2 gallons and I just didn't feel good about keeping it.

I have some powdery mildew this year, the B's and C's I already removed from the vines. I'm going to try an earlier harvest with A's and do a rose style. If I remember right I think I got to 20 brix before they started splitting and drying up. I usually pick at 24 to 25.

Good luck.

 

[nanobrau]

Thanks for all of the feedback. I have just enough fermenter space to split them any which way. I’m glad to see none of you have had serious flavor impact from using mold damaged grapes, so I’m going to give it a try. I will report back with the results many months from now.

 

[NorCal]

I've also had mildew pressure in the vineyard. I would not invest any time in making wine with B or C. Even when I've made wine with grapes between A and B I've ended tossing the wine or made marginal wine that wasn't worth the time. I've been going through row by row and dropping anything with mildew, loss is running around 15%.

Pic from this morning.

 

[buzi]

I've also had mildew pressure in the vineyard. I would not invest any time in making wine with B or C. Even when I've made wine with grapes between A and B I've ended tossing the wine or made marginal wine that wasn't worth the time. I've been going through row by row and dropping anything with mildew, loss is running around 15%.

Pic from this morning.
View attachment 104396

Even with a little mildew they look pretty dang good!

 

[NorCal]

Even with a little mildew they look pretty dang good!

if you look close, there are clusters that I cut off laying on the ground.

 

[Hazelemere]

Thanks for all of the feedback. I have just enough fermenter space to split them any which way. I’m glad to see none of you have had serious flavor impact from using mold damaged grapes, so I’m going to give it a try. I will report back with the results many months from now.

you will have serious flavour impact from powdery mildew damaged grapes.

 

[NorCal]

I’m going through and dropping fruit that is behind and has mildew. An example.

 

[Hazelemere]

IHow to know if you survived a powdery mildew train wreck:

Taste the best looking grapes that you have when they are ripe after hand destemming all of them off clusters to remove as many mildewed grapes as possible.

Press any grapes that taste ok to make a rose. A red wine will be a train wreck.

You might get a decent rose if you are lucky.

Next year spray your grapes with kumulus S and potassium bicarbonate every 2 weeks up to veraison to keep mildew off of the grape skins.

You can't spray with Kumulus S after veraison otherwise you
will end up with hydrogen sulphide in your red wines during malolactic fermentaion.

Trust me on this. I have 130 grape vines and threw out a couple of hundred pounds of grapes last year due to mildew on the skins before I discovered potassium bicarbonate.

Once your grapes reach 16% brix mildew
won't trash them

 

[nanobrau]

I assume you're saying a red will be a train wreck because the mold causes most of the damage to the skins?

 

[Hazelemere]

I assume you're saying a red will be a train wreck because the mold causes most of the damage to the skins?

yes