August 14, 2014

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“What Yeast Should I Use?”

The title of this post is one of the most common questions asked by winemakers working with cold-hardy grape cultivars. It is a simple question, but one that doesn’t have an easy answer. I have written on this topic in the past, so let me just throw out something that you probably haven’t heard yet: your yeast choice probably isn’t going to make or break your finished wine. There. I said it. I diminished the importance of yeast choice. To be fair, yeast selection does have an impact on the characteristics of your wine. Poor-quality fruit can be enhanced by choosing the correct yeast, and high-quality fruit can lose some of its potential by choosing the “wrong” yeast. The argument being made here is that your yeast choice isn’t going to make the difference between a wine that is worthy of a gold-medal, and one that is worthy of being poured down the drain.

Frontenac Gris lined up for sensory evaluation

Frontenac Gris in Wine Preference Study

When yeast choice REALLY matters, it’s when the environment in which the yeast will live (the  juice, and eventually fermenting wine) is inhospitable. Very acidic (pH < 3.2) or very high sugar juice are stressful to yeast, as are very hot or very cold temperatures. Certain strains of yeast are more tolerant than others of these harsh conditions. If for example, you harvest Marquette at 25.5 °Brix and hope to make a dry wine, you’d better make sure that the yeast is tolerant to alcohol levels greater than 15%. Making a late harvest or ice wine? You need a yeast with high osmo-tolerence to handle the high sugar environment.  If you plan on using bacteria to convert the malic acid to lactic acid, you’d better make sure that the yeast is compatible with Malolactic Fermentation (MLF). Do you have a cooling system in your winery? If not, then you probably should pick yeast that can tolerate hotter temperatures. If you plan on cold-fermenting the wine (to guard fruity aromas), the yeast should be tolerant of cold temperatures. All of these planning questions help to eliminate the outright poor yeast choices, then you can get into some of the nitty-gritty details.

Sensory effect of yeast choice. After eliminating yeast strains that won’t work with your juice chemistry and fermentation goals, the main concern is the sensory effect of the yeast strain. In general, cultivated yeast strains will produce low amounts of off-aromas (H2S and VA) when given sufficient nutrients. Some yeast can affect the mouthfeel of a wine by producing higher amounts of glycerol. There are yeast strains that produce high amounts of tutti-frutti ester aromas – great for young wines, but for high-end wines that are going to age a year or more before release, there isn’t much of a point in using these strains. Esters are extremely volatile, and are the first aromas to disappear – sometimes within a few hours of opening the bottle! Other yeasts will enhance the aroma by releasing some of the aroma precursors found in the grapes at harvest. This is all well-and-good, but in the end the yeast can’t do much unless the precursors for these aromas are in the grapes themselves. This is where the big question lies with cold-hardy grapes. For the most part, we know very little about the nature of their inherent aromas. We know that La Crescent is related to Muscat, and has some of the same floral and perfume aromas that are found in all Muscats. We know that it does contain high quantities of monoterpenes, the class of aroma compounds that have these flowery characteristics. However, we also know that Marquette contains significant quantities of monoterpenes, although it is rare to see floral descriptors used when tasting Marquette wines.  Frontenac contains  methoxypyrazines when unripe (similar to the green pepper aroma in Cabernet Sauvignon) and minty aromas (methyl salicylate and menthol).[1] As we learn more about the impact aromas of these grape cultivars, it may affect our decisions for yeast selection. You can read about why these particular yeast strains were chosen for this trial in a previous post.

Yeast trial with cold-hardy grapes. Last year, we decided to ferment the four University of Minnesota grape cultivars with various commercial yeast strains. This was a trial that was sponsored by the Northern Grapes Project, and was replicated at Cornell University with fruit from Vermont and New York. Over the past few weeks, I asked a group of 27 people who all have experience tasting regional wine to participate in a wine sensory panel. The panel consisted of 16 men and 11 women, whose ages ranged from 26 to 74 with a median age of 50. They were served three wines from each of the four grape varieties and asked to rank them from their most preferred to their least preferred. The only difference in the three wines was the type of yeast that was used for fermentation, which is highlighted in the chart below.

Frontenac Frontenac Gris Marquette La Crescent
ICV – GRE Lalvin – DV10 ICV – GRE Lalvin – DV10
Lalvin – Rhône 4600® Anchor – Vin13 ICV – D254® Vitilevure – Elixir
ICV – Opale® Anchor – NT 116 Levuline – BRG Cross Evolution®

The panelists were also asked to write comments on each of the wines. Not surprisingly, many of the tasters noted differences between the wines. On several occasions, it was noted that one of the wines was “far superior” to the two others in the flight, with notes such as “most complex” and “most interesting” written in the comments section. I even had one panelist who stated afterwards (when he found out what the trial had entailed) how he is always surprised by how much yeast choice can “make or break” a wine. In the end, we were testing whether there was a difference in preference for these different wines in order to give recommendations to winemakers. So which of the three yeasts for each grape cultivar were preferred by our tasting panel?

Drum roll please….

For each wine flight, the judges scored the wines in order of preference, with 1=most preferred, and 3=least preferred in the flight. We tallied the total points for each wine and the results are in the charts below. A lower score indicates a higher overall preference (more #1 ranks) by the judges. Statistical analysis was done using the Basker Critical Values for Rank Sum.

Sensory Panel

The small letter next to the sum indicated whether the difference seen is statistically significant (p < 0.05). If there is the same letter next to the sum, then there is no statistical difference in the observed count. As you can see, for every single yeast trial, no clear difference in preference was shown for one yeast over another yeast in this particular trial.  We may be able to say that for La Crescent, there is a trend towards a preference for yeasts that release monoterpenes (both Cross Evolution® and Elixir enhance floral characters in aromatic whites), but we would need to recruit a larger panel to see if this holds true.  However, at this point, there isn’t a clear preference for those yeasts over a more neutral yeast (DV10).

We chose the yeasts for this trial based on their ability to work well within the chemistry limitations of our varieties.  The subtle differences in these wines that may have been observed by individual panelists didn’t translate into a difference in preference for one wine over another for the group as a whole. This is just to highlight why yeast choice probably isn’t as critical as one might think. In the end, it’s a decision that a winemaker makes based on his or her own personal preference and wine-style goals. This is part of the art of making wine. In the  future, we hope to also do descriptive analysis of these wines, to see if these differences can be appreciated by a panel of consumers. Descriptive analysis will also help guide winemakers towards understanding how yeast choice may affect the sensory characters of their wine.

Grape Cultivar – Yeast Used in Trial

Rank Sum*

Frontenac – ICV GRE

49 a

Frontenac – ICV OPALE®

50 a

Frontenac – Rhône 4600®

56 a

*For Frontenac we could only used the scores from 26 panelists due to an error on one score card

Grape Cultivar – Yeast Used in Trial

Rank Sum

Marquette – ICV GRE

54 a

Marquette – D254®

54 a

Marquette – ICV BRG

54 a

 

Grape Cultivar – Yeast Used in Trial

Rank Sum

La Crescent – DV10

63 a

La Crescent – Elixir

52 a

La Crescent – Cross Evolution®

47 a

 

Grape Cultivar – Yeast Used in Trial

Rank Sum

Frontenac Gris – DV10

55 a

Frontenac Gris – NT 116

52 a

Frontenac Gris – Vin 13

55 a

 


[1] Pedneault, K. (November, 2012). Canada: Maturity and Quality of Some Hardy Grape Varieties Grown in Quebec. International Conference Neubrandenburg and Vitinord. Neubrandenburg/Szczecin.

 

 

Making Wine with Marquette (Vintage 2011)

 

Yesterday we harvested all the Marquette out at the Horticultural Research Center (HRC). Since I haven’t written anything about this grape, I figured now was a good time to write a little post on it. I really like the potential we have with Marquette. When it’s done right, it makes a lovely dry red wine with similar aromas to Gamay or Pinot Noir. Unlike these two grapes, however, Marquette is a teinturier variety so it is very highly pigmented. Like Pinot Noir, it is low in tannin.

Like many of our Vitis riparia-based hybrids, it leans toward high sugar and high acidity.  All of our Marquette harvested this year came in with an average Brix of 26, and a TA around 10.o g/L. Obviously a red wine with 14-16% alcohol and searing acidity (those acid numbers are more typical to Riesling) doesn’t sound all that pleasant, but with some slight adjustments, it makes a nice red wine.  Here’s a summary of previous harvest data with Marquette at the HRC. As you can see, high sugar and high acidity. In good years, it comes in with a more manageable TA of less than 10 g/L:

Here’s what we’re working on in our optimization trials with Marquette this year:

1) Ways to increase tannin concentration/extraction

We divided one lot into 3 different fermentations. Last year we experimented with leaving 50% whole clusters (uncrushed) for one Marquette fermentation, and the results showed a marked increase in tannins. The flavor and structure of the resulting wine was nice, although I think it would be a good blending component rather than a wine to drink on its own. We are trialling this technique again this year. However, we didn’t have the ripeness that we had last year, so I imagine we’re going to have a bit more “green” character to the wine. It will be good to have a comparison over different vintages, regardless. With a second trial, we removed 20% of the volume of juice from the must in hopes of concentrating the tannins that are extracted.  In the third trial, we froze the grapes solid (at -20°C), hoping to rupture the cells in the skins and seeds to facilitate tannin extraction. We’ll keep you updated as to how the resulting wines turn out.

2) Yeast Trials

We have been pretty happy with the results of using yeast strain D254 on Marquette. It tends to help bring out the black pepper aroma in the grape, and minimizes any green/herbaceous character. We  are doing more trials with D254 this year, but also threw in two Burgundy yeasts: RC212 and RA17. Because of the high potential alcohol of our Marquette, we bled off a portion of the juice (about 15%) from the must, and added an equivalent amount of distilled water back to the must in order to bring the Brix down to 22 (a fairly standard practice in warm regions with high sugar levels). This had the double effect of also bringing down the TA a bit to around 8 g/L. Using distilled water ensures that there is only a negligible increase in pH.  By removing a portion of the juice prior to the amelioration, we hope to keep the skin/juice ratio the same. This will hopefully help diminish any perceived dilution of flavors.

3) Sparkling Rose

With all the juice that we ‘bled’ from our Marquette, we decided to make a sparkling rose. We will be making it using “Methode Ancestrale” rather than the Champagne method. In this method, fermentation is stopped by chilling the wine to zero celsius about half-way through fermentation.  The nearly clear wine is then racked, and allowed to restart and complete fermentation in bottle.  Usually there is a negligible amount of lees remaining, so the wine doesn’t need to be disgorged. I’m planning on having a finished wine with about 12% alcohol, 9 g/L TA, and 50 g/L residual sugar. We’ll see how it goes…

 

Frontenac Harvest Data from 2001 – 2010

Here’s a look at some of our harvest data over the years for Frontenac. As you can see, we have a lot to deal with in order to try to balance the acids in this variety. For this reason, many people have found success making a fortified dessert wine or an off-dry to sweet rose-style wine with this grape. Frontenac was the first grape variety released by the U of MN explicitly for wine production. Although it’s chemistry differs from what we see with classic V. vinifera varieties, it has been shown to make some good wine. The previous enologist working at the U of MN has lots of experience with Frontenac (she even wrote her dissertation on it). Here is a link to an article she wrote for winemaking recommendations for Frontenac.

La Crescent harvest data

A while back, when I first started this blog, I wrote a brief post about the grape variety La Crescent. At the time, I promised to compile our vintage data and put in some charts or graphs illustrating some of our data. Well, I’ve been trying to work out some cool charts that compare various vintage parameters, but it turned out to involve way too many factors and be too complicated to give any significant data. So, I’m just going to post our harvest data information below for now. As you are all well aware, we get some very high acidity in La Crescent (like the rest of our hybrids). Remember that wine with a TA > 10 g/L will taste sour, so it is important to use various deacidification techniques, or leave enough residual sugar to help balance the acidity. More on that in a future post…

Get to know La Crescent!

La Crescent

Local Twin-Cities magazine, The Heavy Table, recently wrote a really great article touting the wonderful qualities of the La Crescent grape last week. I too was impressed with the quality of La Crescent as a wine when I first tried it. It has some very nice tropical fruit aromas, and can be made in a variety of styles. I truly think that Minnesota is an excellent white wine climate (which is true of most cold areas). I realize there are a lot of sources already available for you to learn all about the wonderful sensory aspects and general viticulture and enology information regarding this variety, so I won’t go into too much detail on that aspect.  Here is the University’s description of La Crescent. And, just in case that wasn’t enough for you, here is Lisa Smiley’s summary of La Crescent. For those of you who don’t know Lisa, she’s done some great work summarizing the history of all known cold-hardy cultivars. This was done as part of her Masters of Agriculture degree in 2008 from Iowa State University. 

I’ve been working hard the last month or so compiling lots of old vintage data, and as soon as I figure out how to post charts and graphs on this blog, I’ll share that information with you (hint: can anybody tell me how to do this?).