Let's Get Technical - Current UC Davis Wine Research Seminar 2025

UC Davis recently held a presentation of current research topics at Greystone in St. Helena on both winemaking and viticulture research. I highly recommend attending these meetings when they pop up since they are affordable and quite interesting. Below is my rather simple summary of the presentations.

1.        Red Blotch – This is something we too have in our Lake County vineyard that is spreading throughout California. A link has been established to native California grapevines which suggests that red blotch has in fact been here all along with a native vine resistance indicating that. It is spread by TCAH (Tee-ka) otherwise known as the three-cornered alfalfa hopper. The hopper does not travel far and lives mostly below the canopy in the ground cover, but it moves up to feed and can migrate short distances in irregular bursts.

The challenge is that there is a 3-year latency period from the initial vine infection. So, if you are seeing that characteristic red-leaf pattern all of a sudden, you were probably infected three years ago, and it has since spread. We have vines in Lake County that came with red blotch as dormant grafts due to bad nursery practices, and it is spreading through insects.

Davis now recommends pulling individual vines if a singular isolated example shows up, but if two or more are present, they recommend pulling all vines within a 30’ radius and replanting. There is no known cure, and the vine decline is variable. It can work out for a while, balancing sugar with lower brix accumulation and more “rustic” flavors, but vine decline is inevitable, and infection spreads in the meantime.

2.        Sensory evaluation – Many of us taste wine in barrel and sometimes create blends on the fly when working at small wineries, this is part of the business. The key is knowing what sensory threshold you are bad with (or strong in) and making sure you have someone with the opposite tasting profile partnering with you when tasting. For example, 50% of the population can’t smell “rose” (b-damascenone) in wine, and the sensory threshold ranges in the 50% that can by 100,000x!!!

The big takeaway for me was a reminder of how important a middle of the road reference standard can be when having to make quick decisions, but that means first that when tasting with others we need to agree on what words mean first off in addition to knowing our own palates. But second, an easy trick is to compare with another sound bottle. For example, if you are trying to work Merlot into a tannic Cab with a Bordeaux framework, you really should pop open either a benchmark Bordeaux-blend bottle or a solid if generic one, verify that it is sound, and use it as a springboard for comparison. We all get tunnel vision, whether in the cellar, at a wine competition, professional tastings or other critical tasting moments, especially in a room filled with barrels, sub-threshold smells and bad lighting. You also need to taste regularly – this is often the difference between an amateur and a professional who is consciously building the mental rolodex and procedural profile. Set yourself up for success and fight cellar palate, or balance it with counter-palates.

3.        Smoke – We all (in the North Coast) have measurable smoke in our 2020 wines. I have it in my Lake County wines and the nearest fire was much farther away than other counties had it. In fact, I tasted it in all the 2020 Contra Costa wines with the wine panel. A few new compound families have been discovered, and new synergies between low-levels of compounds such as fruit masking have been verified. In tests fresh smoke only needs ten minutes to absorb into a grape berry next to a fire. Of course, our challenge was long, low exposure to smoke that had diminished compounds. Further complicating low-level exposure is the human factor due to a taster’s sensory threshold (yes it is true that many scotch drinkers don’t notice smoke) and specific enzymes profiles within saliva. From the winemaking standpoint, limiting skin contact beyond fast whole-cluster white winemaking doesn’t do much since more smoke compounds have been discovered within the grape pulp the previously thought. There is a new “black box” treatment to knock-down levels of some compounds, but not when they are working synergistically with other compounds, and there is a real complexity of forces at work.

The general guidelines if we have a fire-year still hold the same though. Assuming the fire is more than a few miles away you can just make white wines, avoid toasted new oak barrels or chips, minimize pressing, leave a little sugar which keeps some of those compounds bound, or build a red so big that it “floods the zone” with other flavors so that smoke is suppressed as a sensory experience. Everything is a trade off. Also, grapes vary wildly in their susceptibility with Petit Verdot, Mourvedre and Pinot Noir being very sensitive, Sangiovese on the high side, Cab and Merlot are medium, and some cultivars like Barbera are strangely low. It has no correlation to skin thickness, and the science is still out on how the grape’s bloom helps in the process, but that is in the works.

4.        Soil minerals – An ongoing study measuring identical Pinot Noir clones and roots planted across seven different regions. This is essentially a how-do-we-get-terroir study, and indeed since minerals act as enzyme cofactors, different fruit expressions seem to result, as much as weather can be eliminated as a factor, which is it absolutely can’t be eliminated.

Minerals also have a strong influence on a wine’s reduction/oxidation potential as we know, and very mineral wines can be highly reductive as Clark Smith has been saying for decades (read your Postmodern Winemaking book, then use the knowledge for different goals) with very different expressions and needs. This study is ongoing, but unfortunately there have been some perplexing decisions made in executing it, and some of the choices were really bizarre.

This is an important topic from a grape-growing standpoint, and what is going on below the surface may be more important than what we can see in driving wine style. Plus I really want some data to fight all of these losers claiming that minerality doesn’t exist, terroir is fake, and other somnambulating rookeries.

5.        Native California yeast strains - The topic of “natural” or spontaneous (uninoculated) fermentations continues. Yeast do breed and cross in nature. A large study has found a few interesting things, the first being that native oak trees are reservoir and incubator for saccharomyces yeast. The second is that a massive wine yest gene experiment has found that there are three clusters that have appeared consistently, one cluster is a huge family that isn’t particularly strong on oak trees, a second cluster is our inoculated strains which are mostly European isolates/selections, and the third cluster is the evolving interaction of these two groups, leading to an arguable California oak-derived synthesis of native and European yeast! This family is growing and evolving rapidly in winemaking areas.

This kind of cool (or dangerous) as yeast evolve rapidly, and native oaks are acting as a giant petri dish that may have some local terroir residue.

Much of this research also looked closely at Twomey fermentations in their two winery locations nearby. Of interest, what they found in the second half of the fermentations as the wines go dry, is that the “in-house” cultured yeast – and they had particularly strong cultured yeast like EC-1118 and Uvaferm present in the cellar, in fact did not carry out the fermentations to completion. The spontaneous ferments had a 1 or 2% population of these strong commercial yeasts, but in fact it was these hybrid local yeasts and spontaneous actors that did most of the heavy lifting, and had significant effect in DNA analysis. The price was a little more VA, and the big question remains of how much sulfur gives a level of security and how much destroys the native mix. Some people go spontaneous but add 50ppm SO2, which is pretty much guaranteed to incapacitate most of the more delicate spontaneous yeast, 20 ppm is a common “soft” approach, mostly to suppress LAB, though wine pH and temperature are hugely important, as well as fruit quality.

One last interesting yeast point, AMH yeast was used as a control, and the spontaneous ferments all went faster than the AMH fermentations. I have had trouble with AMH when it conflicts with another yeast strain since it is very sensitive and can go supernova. That this particular yeast strain is indeed so slow is a usable bit of info for winemakers if you want a real low and slow inoculated fermentation. Just don’t mix it with other more vigorous strains.

To be continued…