Ensuring clean wines: how do commercial wineries do it?

I'm sure that many wine lovers have experienced this before. You sample wines at some small country winery and sometimes the wines simply do not taste clean; they may look alright and be free of other common flaws like volatile acidity or turbidity, yet they may have a generally "dirty", contaminated taste that hints at imperfect cleanliness somewhere during processing. I've encountered such wines at small wineries but also when trying some people's homemade wines - some of which are really dirty and I can't imagine how they can be enjoyable.

What has interested me for some time now is how commercial wineries actually manage to turn out clean wines when dealing with large quantities. Strict sanitation of the equipment is a no-brainer, but given that grapes aren't hosed down prior to harvest and all manner of debris can and does make it into the hopper prior to crush, why do the resulting wines that you buy commercially generally taste clean and free of that nasty dirtiness that can affect low-tech wines? Is it filtration that somehow removes off-flavours that might come from dust, bird poop and whatever else? A truly perplexing question.

On the flipside, if you are making small quantities of homemade wine and observe strict sanitation and hand-harvesting and separation of grapes from stems and other debris (and use neutral fermentation/storage vessels like glass), you can be generally sure that your wine will be okay. Even though I do this personally, at times I swear I can taste a bit of the dust that coated the grapeskins before I crushed them - and no, I don't wash the grapes beforehand nor do I filter my wines afterwards.

It all boils down to how wineries manage to produce clean wines when dealing with such large quantities where there are more opportunities for contamination along the way...

Paul,
There is an assumption implicit in your question that I have my doubts about, namely that the "dirty" flavors in flawed wines are due to debris that finds it way into the fermenter. My own guess is that that is rarely if ever the cause. Instead, I'd guess that microorganisms present on the equipment and in the cellar are the usual suspects and can be avoided using proper sanitation. Hand sorting of grapes will remove any large quantities of debris and what is left will be insignificant. I'd also question your assertion that large-scale operations don't have such problems: tasted any Coturri wines?

Mark lipton

Ahhh, yes - I was not clear because I should have explicitly excluded bacterial spoilage as a culprit. I was actually thinking about the flavour of dirt in the wine - whatever it might be, whether dust from an adjacent access road, or diesel soot covering the grapes; that sort of thing.

I haven't tried any Coturri so I don't know what the source of that particular dirtiness would be. That said, I wasn't thinking of bacterial spoilage at all.

I wasn't thinking of bacterial spoilage at all.

If you weren't, then you are talking about a perceived taste, and not a particularity. No one can answer the question of your perception.

Like Mark, I suspect you are in fact talking about microorganisms, but you don't have their identity.

Paul - I think the problem you may be referring to could be attributed to not performing the first racking soon enough. If, after crushing and pressing, the fermentation completes it's phase, it there is any vegetal matter, from the pulp or skins, residing in the lees, it can rot and impact off flavors. My motto is "Rack early and rack often".

Doggone it, Howie, that could very well be the cause. Thanks for that eye opener; it makes sense to me.

I've encountered such wines at small wineries but also when trying some people's homemade wines - some of which are really dirty and I can't imagine how they can be enjoyable.

Who are you, and what have you done with Paul B?

Bird poop???

Bird poop???

That ain't Superman flying over them grapevines whilst taking a dump.

That ain't Superman flying over them grapevines whilst taking a dump.