Archive for the 'Viticulture Practices' Category

Eucalyptus

Sunday, June 26th, 2005

Summary: 1)eucalyptus aroma is produced by at least one grape variety.
2) a common monoterpene found in grapes is a precursor to eucalyptol, indicating that this aroma could be an indication of age in certain wines.

What is the liklihood that eucalyptus trees near your vineyard are going to impart eucalyptus aroma to your wine? Certainly it is not difficult to smell eucalyptus when several trees are around and it seems logical that if you can smell it in the air than the volatile compound could potentially settle on grape skins. Fair enough? As far as I can find, no study has been published demonstrating that this occurs at levels which would impact wine aroma, thus bolstering opinions in either camp. But not finding something to be true does not make it false and vice versa. One recent study (published in In Proceedings of the VIIe`me Symposium International d’OEnologie. Actualites OEnologiques 2003. Bordeaux, Francia, 2003; i.e. limited peer review, cited from study below) found Eucalyptol in wines from vineyards surrounded by Eucalyptus sp. trees, though it was not shown that the aroma came directly from the trees.

Before cutting down some of these beautiful giants, look at this recent study that demonstrates the production of eucalyptol (1,8-cineole, threshold of about 2 ppb) in Tannat grapes. Furthermore it was shown that limonene (an apparently common grape monoterpene giving citrus - orange, grapefruit, lemon - aromas and used in bergamont) can undergo reaarangement in acidic media to form eucalytol (slow reaction, white wine pH). Of course this doesn’t mean that the aroma cannot come from trees, but it does mean if your wine smells of eucalytpus, it could have come from the grape itself.

Naturally this begs the questions: how does our viticulture impact the formation of this compound? The aforementioned study shows its concomittant increase with sugar after veraison. Light can increase monoterpenes in general suggesting this may also increase eucalyptol or at least its potential to form after ageing. We’ll just have to wait. Finally, I will note that Tannat wines are purportedly well known for this characteristic and I was unable to find reports on the amount of eucalyptol or limonene in other varieties.

Vit Practices: Color and Cab.

Friday, June 24th, 2005

Here is the bottom line on this fairly well done study: Increasing your hang time will impact your color. However, there was no difference between 1 and 2 weeks after ‘normal’ harvest dates. Although the authors try to sell this as a study about ‘wine quality’, no sensory work was performed and they really only looked at color. Nevertheless, slightly riper grapes seemed to have a little better color stability after 18 months. Reading this article after another recent gem on light and color highlights the possiblity that looking at total phenols, or phenols in general is largely deficient in determining quaility (an opinion I am developing). The grapes used here may have had more color later, but what about vegetal, peppery, or fruity flavors? Was there a difference at all in characteristics such as these? It seems to me most of us would take the diminshed color at ripening stage 1 (about 22.5 Brix) and subsequent lower alcohol if we were confident the flavors were delectable and weren’t going to get any better. But do they get better? Or just stylistically differnt? If you want a summary of study details see below.

Perez-Magarino, S et. al: J. Agric. Food Chem. 2004, 52, 1181-1189
Tinto Fino (TF) and Cabernet Sauvignon (CS) were used to assess the effect of the degree of grape ripening primarily on wine color. Color changes durig ageing of each treatment was also examined. The levels of flavanols, anthocyanins, and derivatives of both types of compounds, were assayed immediately after fermentation and at different times during aging in American oak barrels and in the bottle.
The ripening stages were approximately as follows:
1)conventional’ 22.5 Brix, pH 3.36, TA 7.76 (CS) ; 2) 1 week after (23.6 Brix); and 3) 2 weeks after (~24.2).

Fermentation between 25 and 28 °C with 40mg/L SO2. The maceration time was ~ 14 days. Pressed at ~ <3 g/L sugar, transferred into barrels where malolactic fermentation and wood aging were carried out.

The results showed that “maturity date” or “ripening stages” effects were detected, but these are different for each individual component as well as for each of the two grape varieties studied.

In general, the dimer and trimer flavan-3-ol derivatives reached higher levels in the unaged wine made from the grapes collected on the later harvest dates which indicated that the degree of flavanol polymerization increased with the degree of grape ripening. However, this was only true in the CS. The TF had its peak in the middle ripening stage. There seemed to be only small differences between ripening stage 2 and 3, and certain compounds were even statistically higher in stage 2 than in stage 3. No difference in total phenols existed between stages 2) and 3).

WINE AGEING: “No clear trends with grape ripening were observed. In fact, the CS wines with the highest color intensity values were the wines made from the grapes collected on the 2nd harvest date.” The wines made from more mature grapes had higher levels of flavanols and their derivatives. The free anthocyanin content decreased sharply during aging, the greatest losses taking place in the first months of aging. After 18 months of ageing, any initial differences in anthocyanins and its derivatives (termed ‘new pigments’) due to ripening stage were virtually erased. However, color intensity differences were maintained after 18 months and in all cases the percentage of blue increased as ‘new pigments’ increased (i.e. anthocyanin products that are not antho-tannin complexes). Wines made from ripening 2) & 3) showed higher levels in these ‘new pigments’, in both TF and CS wines.

Summarizing: delaying harvest date between 1 and 2 weeks produced grapes with greater color intensity and a higher percentage of blue pigment. This increase in anthocyanin derivative levels contributes to color stability by maintaining color intensity and increasing the blue component.

Additionally, the results showed that the amount of time the grapes are left on the vines may need to be limited, because wines made from the grapes collected on the 3rd harvest date did exhibit better color quality characteristics than the wines made from the grapes collected on the 2nd harvest date.

Vit. Practices: Colorado

Wednesday, June 22nd, 2005

Of course, as soon as I suggest a title format, I find something that is hard to fit under one of our headings. Nevertheless, this pdf is mainly a viticulture survey of Colorado’s plantings and varietal selection. This is a nod to my buddy Rob who makes wine at Two Rivers Winery in Grand Junction and our alma mater conducted the survey. I just thought it may be interesting to see what is going on there. An ‘up and coming’ region (which these days - no offense Rob - seems to be any region that is not CA). Its pretty easy to breeze through the figures and get a general idea of what’s going on, for curiosity’s sake. Here is some other info on CO wine: coloradowine.com