White mildew on grapes - cleaning?

Winemaking Talk - Winemaking Forum

Help Support Winemaking Talk - Winemaking Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Sep 15, 2022
Reaction score
A very friendly neighbor graciously let me harvest their grape vine since they weren't using it, which is awesome. However, since they weren't taking care of it, the grapes have some pretty widespread powdery white mildew on them. I washed them with water before freezing them but it's difficult to get it all off. Will it be much of a problem? How do I better clean it? Would any risks it poses be fixed with a crushed campden tablet in the must or pasteurization anyway? They tastes fine themselves.

Also, something mildly interesting, there's actually two vines, one has green grapes and one with dark blue grapes, and though they're pretty intertwined only the dark grapes have the mildew on them. Isn't that weird?
I'm not positive on the species, I live in the PNW, I think they're just two different types of concord? Either that or the green one is riesling or close to it? It tastes really sweet and acidic. No idea really, just going off of cursory research, I'm sort of an amateur with grape wines. I'll post pics if it's of interest.
First, welcome to WMT
Food processing rules; mildew on the grape doesn’t matter. One can “kill” off surface fungus by having low pH and alcohol above 5%. You noted that taste is good which leads to finished wine should taste good ie this is a cosmetic issue. My look at wine is that the process is a series of cleaning steps as removing fermentable sugar, removing hazy solids in the liquid, removing gross solids and insects, etc.

From a farming point of view mildew weakens the plant, the neighbor will get better yield and possibly more sugar/ more aromatics. ,,, It is normal to have some white dustiness on grape skin. A true fungus will show up on new growth leaves and stems, ,,, was this just on berries?
Any idea what kind of grape?
Last edited:
was this just on berries?
Any idea what kind of grape?
Just on the berries yes. In the original post I speculated on what kind of grape it is, pretty sure it's concord.

I've also heard that the white stuff is actually wild yeast? But it also does have other symptoms of mildew like splitting.
You can make bad wine from good grapes, but you can’t make good wine from bad grapes. I would exclude the clusters with mildew on them.
Well, to me it isn't about making good wine or bad wine, it's about making any wine at all. I do not and have never had access to any fresh grapes like this and I want to use it.
Do you have pictures to share? It might be easier for us to say whether it is ‘la pruine’ (bloom) on the grapes or mildew.

Sorry it took so long to respond, I've been busy making cider in the meantime.

These are the grapes, maybe yall can help me identify them with these too.

I think I'll go with the rose idea @ChuckD provided anyway though. And a white with the green ones.

Still a little difficult to say from the photos but I’d say powdery mildew. If you really want to use them, I’d agree with the others to press them directly and not macerate. As to why it’s on the red grapes and not the white: some varieties can be more resistant than others. You’d probably do better next year if your neighbors will let you spray some sulfur at least at bloom and berry set since it does look like the leaves are unaffected. Also looks like they would benefit from some pruning and crop thinning.