The most seasoned berry sampler would know. Majority of people on this forum probably wouldn’t be able to help much.
On the other hand, the members would for sure be able to recognize the difference between a wine of Screaming Eagle quality vs. $20 California Cabernet. What I love to test is can people sniff out a $50 bottle vs. $150🤔
Now that Robert Parker has retired, this is essentially impossible. 
Eric, I commend you for taking a stab at this.
probably the most important thing here would be to taste the grapes.
Alan did ask in his OP what differences in the taste of the grapes would be notable.
From a couple of experiences tasting wine grapes at harvest time the thing that really struck me was how sweet they were. The sweetness was overwhelmingly dominant to my untrained palate. I’m sure I couldn’t tell the difference between high-end grapes and those destined for plonk. I figured that’s just because I have no experience or knowledge.
What I got from Eric’s posts is that even from an experienced winemaker’s perspective it would be easier to tell from visible differences like uniformity of ripeness and freedom from leaves that are clues to how much care was taken in the vineyard than by taste or chemical analysis.
Smartass answer: peek at the paperwork showing where they’re from and how much they cost.
David- Wine grapes are ~25 % sugar (ripe cab can be 30%), tablegrapes are 17 - 19% sugar. You can get used to the sweetness but it is important to spit when you’re tasting during harvest…
I do understand the theory behind looking for visual cues but for me taste is paramount.
Taste and visuals. I custom crush at a facility which will have multiple bins of fruit being processed from different vineyards. I taste them all.
The high end wine grapes just taste better - I can’t think of another way to put it. They taste balanced, just like your high end wine. The bin will contain very little MOG (material other than grapes). It will contain a uniformity that is not visible in the low end bin.
Thanks Casey!
Btw, when judging ripeness for picking, I’ll crush some grapes in a bag and smell the juice…that lets me know what’s going on and translates better to the final wine (esp in lower brix situations) without being distracted/influenced by the sugar flavor.
Uniform ripeness helps achieve a certain elegant style. That might be a sort of truism for most modern Napa Cabs, but it is definitely not true for many great wines. A range of ripeness provides complexity. You obviously want to stay within certain parameters to avoid green and raisinated tastes. Do you just want dense black fruit, or a range of red to purple to black? Maximized aromatics may come in the later red phase, while having all of the grapes at that ripeness level may not make the best wine. So, you can have a sort of field blend from a single variety from a single block of a vineyard. You can be very labor intensive in managing that exactly how you want.
As far as leaves go, some respectable winemakers don’t mind or even prefer some fully brown dried-out leaves, believing they add a tea character. Obviously, green leaves will bring green flavors. Not sure I’d ever be comfortable with brown leaves, but I’ve had plenty of wines that got some and didn’t suffer for it.
With as many tons we have to pick per day we bust our ass to keep MOG at a minimum. We usually have about 20 pickers, 2 bucket dumpers, and 2 leafers. When dumpers aren’t dumping they try to help with leaves.
When we picked per ton rather than per bucket the pace was slower and easier to monitor leaves. I too believe there’s nothing wrong with some variation in ripeness as long as it’s not BDX stuff as you can get green vegie flavors.
It’s great how the smartasses have had their turn and now people who know what they are talking about are chiming in. Love the discussion and learning!
So if a lot of this is based on appearance of the grapes doesnt that mean the farming aspect is more important than the terroir ?
Yup, really enjoying the posts here from those ITB.
Agreed - this high tech business of crushing berries in a baggie is universally used, near as I can tell. You say you do it in order to smell the juice. We all do that. And we take note of how the color comes on in that high tech baggie. But Eric - can you honestly say you resist the urge to confirm your olfactory sense with the secondary check of the refractometer? I can’t resist. It is like blind tasting finished wines - don’t you want to know what was REALLY in that blind bottle?
Alan - terroir (in my book) is a combination of soil and weather. Farming is dictated by both these components. Bringing in good-looking fruit means that the farmer has maximized his influence on the terroir. But don’t ever believe a farmer is in total control of either what is going on in the soil or overhead in the weather. It’s different each vintage, and many times during each vintage.
I’ve been told …so it’s just a guess that many of those highly sought after and highly rated Napa Cabs are picked at very ripe levels (like 28-30 brix) and acid bumped and watered back. I think that’s how they get that super rich/sexy character. I’d bet they sort out any shriveled berries to stay away from those raisin flavors. We always called them 4x4 wines…4 ph and .4 acid.
When in the field, and after a number of years of doing this, in same vineyard/rows, one should be pretty much able to “call” numbers. Once the fruit comes in, then sure, you always run numbers, and you do pull berries from various areas/clusters of the bin, squash and blend the juice first. But, in general, you taste for certain flavors when you call a pick. Numbers, like Eric has said, are not always a direct correlation to flavors, with vintage conditions playing the part. Even at same Brix your acidity will differ, year to year, for example. Numbers are arbitrary, flavors never lie.
I used a refractometer once or twice, as a newbie, waaaay back. Its pretty much new, in the box, somewhere in the garage.
I check the brix…smelling the crushed grapes isn’t the only thing I do regarding picking. Sometimes I’ll get the TA, if I think it’s interesting. I track the ‘snotball’ development, the number of days & how warm it’s been since 90% veraison completion, and various other things that are always exciting at the time!
I commented on the grape juice smelling thing cuz of Matt’s comment on ‘the most important thing here would be to taste the grapes’, just to throw out a different perspective. Maybe I should have made that a bit more clear 
But I don’t taste the grapes (generally, once in a while I do) cuz, for me, the sugar gets in the way of making sense of what’s going on…but that’s just me I guess. Course, I don’t make Cab Sauv, which likely is a different kettle of fish (I am making Cab Franc now tho).
Definitions:
Snotball: as grapes mature, the inside goes from rock hard, to firm, to semi-firm, to liquid…the stages in the middle are gelatinous and referred to as a snotball.
I thought a snotball is one of the pitches in MadBum’s arsenal.
Ive never thought of weather being a part of terroir, take that famous crossroads in Burgundy where you have Montrachet one corner, Batard montrachet another and then two much cheaper crus opposite. Now i can fully accept the terroir and farming having an effect, the terroir being the elevation, slope, soil etc but i cant accept the weather changing within 20 yards, between regions and even on large topology changes say 500 ft of elevation but not walking a few feet.