September 6, 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.

 

 

Frontenac Gris Rosé

I realize I am WAY behind in updating this blog. I will try to remedy this in the coming weeks.

I have a lot to write about, as we recently finished our tasting evaluations of our 2011 wines. Although the majority of the wines we evaluated are Minnesota selections that haven’t been released, we were also able to do some evaluations of our trials with Minnesota cultivars. Today I’ll talk about one of our trials: Frontenac gris rosé.

There are two methods one can employ to make a rosé wine. The first, which I mentioned in my Marquette vinification trial post last year, is the saignee method or “tank bleeding.” Essentially you fill your tank with red grapes, and do a cold soak for anywhere between 6 and 24 hours. This allows time for some of the color from the skin of the grapes to seep into the colorless juice. The longer you let them soak, the darker the color. After the desired soaking time has passed, you open the racking valve at the bottom of your tank (with a hose attached, of course), and pump 5-10% of the volume of your tank into another tank. Then, you ferment your red grapes to make a red wine, and your saignee juice is fermented as a rosé. Of course, this method is typically employed with Vitis vinifera grapes, of which most have colorless  pulp. Most of our hybrid grapes have colored pulp and skin, so this maceration step is unnecessary if you wish to make a rosé from Frontenac or Marquette. Often the problem with Frontenac rosé especially is that its color is more of a claret rather than a rosé – even without any skin contact!

So that brings me to the second method of making a rosé. The French would argue that this is the only way to make a rosé (unless you’re in Champagne). It’s the direct press method. This how I would recommend rosé made from Frontenac or Marquette should be done. With the saignee method, it may be difficult to achieve a lighter-colored wine. With the direct-press method you essentially treat the red grapes as if they were white grapes.  You press the grapes right after harvest and can crush/de-stem, or press them whole-cluster. If you whole-cluster press you may be able to achieve a lighter color because of adsorption of anthocyanins to the stems.  Of course if you were using Vitis vinifera like they do in Provence, you would need a short maceration time to achieve some color extraction. Traditionally, the grapes would be crushed, de-stemmed, and macerated for a short period of time. Maceration often takes place directly in press.

Although I mentioned Frontenac and Marquette as two red grapes that can be used to make a rosé, there is a third option: Frontenac Gris. Frontenac Gris does not contain anthocyanins (red pigments) in the pulp like Frontenac. However, it still retains some red color in the skin. If you press the grapes immediately after harvest, it yields a gold to amber-colored juice. But, if you allow a certain amount of skin contact (or if you over-extract during pressing), you can extract some of the color from the skins. Thus, it is really the only grape we have that can be handled as one would handle V. vinifera when making a rosé.

Knowing that Frontenac Gris isn’t as highly colored as a red grape, our skin contact time needed to be longer than the 6-24 hours traditionally needed for making a rosé from red (vinifera) grapes. We decided to do two trials: a 3-day pre-fermentation maceration, and a second where we actually fermented the grapes on the skins. We already knew that fermenting Frontenac Gris on the skins (when we made a FG port last year) gave us a really pretty dark pink wine, so I wasn’t too worried about too much color. The idea was to see what we could achieve with maximum anthocyanin extraction during alcoholic fermentation. It’s important to remember that a certain percentage of color will be lost immediately after fermentation. Another percentage is lost with sulfur addition. So, if the color of your wine doesn’t resemble the color of your juice, then this is why.

So here’s a picture of the color difference between our two trials. See if you can pick out which was a 3-day cold soak prior to fermentation and which was fermented on the skins:

If you couldn’t figure it out, the wine on the left was macerated (cold soaked) on the skins for 3 days, while the wine on the right had a 3-day cold soak plus spent a week on the skins during alcoholic fermentation. While the color from a photograph isn’t always indicative of what it looks like in real life, it gives you a good indication of the final color difference in the wines. The 3-day cold soak was more of an orange/salmon color. It wasn’t exactly rosé, but it wasn’t terribly unattractive either. It all depends on what the winemaker is looking for in their final color.

While Frontenac Gris doesn’t have anthocyanins in the pulp, there still tends to be a high amount of other colored molecules. I think the high quantities of these yellow/gold pigments mixed with a small amount of red yielded a wine that had more of an orange/salmon color.

Another great thing about using Frontenac Gris to make a rosé wine is that there are almost no tannins in the grape, thus by fermenting on the skins you don’t extract heavy amounts of tannins. Nonetheless, there can be bitter and herbaceous elements that are extracted from the seeds, or from the skin of fruit that is underripe.

Here’s the breakdown of the chemistry in the finished wine

TA  (g/L )                  pH                  Alc. %

Frontenac Gris – AF on skin

            9.20

            3.50

       15.4

Frontenac Gris – 3-day

          10.45

            3.41

       15.4

An interesting note from the fermentation on skins is the decrease in total acidity and the increase in pH. This could be due to some excess potassium extracted from the skins that may have facilitated tartrate precipitation as well as increasing the pH. Since we didn’t measure potassium, this is only a guess. However, the final chemistry of the two wines is pretty close.

As for how the wines taste, I’ll leave you with some of the tasting notes from our evaluation. The wines were tasted blind by our viticulture and enology crew.  Both of these wines were fermented to dryness and no adjustments were made post-fermentation. This was to ensure that they followed our standard protocol for winemaking. Some slight adjustments to the acidity or sweetness may have yielded wines that were a bit more balanced on the palate. You can see that there was some herbaceous character noted in the grapes fermented on the skins. Some tasters found it off-putting, while others enjoyed it. It is also possible that some fining could help remove some of these bitter compounds. In the end, I hope this trial at least gives you some tools to use in your own wineriess.  Cheers to some tasty rosé wines… just in time for summer!

 

Color (3-day cold soak pre-fermentation) salmon/orange
Aroma white chocolate, apricot, fruity, red fruit, artificial cherry, strawberry, berry, banana, hybrid, plum, soapy, some bakers spice, dried apricot, concentrated raisin, petrol/chemical
Palate acid, good citrus/peach flavors, some bitterness, tart, hot, different, red fruit, tart, berry, nutty, sour, peachy, berry, cloves

 

Color (Fermented on skins) dark pink, vibrant red, rose, pretty garnet
Aroma cherry, oregano, more riparia, lots of red hybrid, Frontenac flavors, herbaceous, blackberry, camphor, green pepper, cherry Robitussin, raspberry, cherry
Palate acid, hot, chemical, cherry, bitter, takes on more hybrid flavors, blackberry, black currant, herbaceous, thin, hybrid, underripe, red currants, cherry, plum, chokecherry, some bitterness, hot, cherry, raspberry, spice

 

 

Passito… or Essencia?


Here is an update on my attempt to make a passito from Frontenac Gris…

After about 2 weeks of drying in the  greenhouse, the grapes had lost about 50% of their moisture. I decided to press them at this point, not knowing how well our tiny little hydropress would do with raisins! I had close to 10 kg of grapes (ahem, raisins) that I pressed, and got about 2.5 liters of “juice” from them (the consistency was more like syrup). I think a commercial press that went through a long series of slowly increasing the pressure might have gotten a bit better yield, but I was happy with what I got. The resulting juice/syrup was a deep amber to brown color. There was a slight copper tinge to it. We’ll see what the color is like after fermentation.

Now on to the most spectacular result…

At just 50% dehydration, I didn’t know what to expect for sugar numbers (I think typical passito is dried a bit further). However, I think I didn’t need to dry them out quite as much! The extracted grapes had a sugar concentration of 55 °Brix! That’s INCREDIBLY sweet! That’s the equivalent of almost 700 g/L (70%) of sugar. Coca-cola contains about 111 g/L of sugar. Maple Syrup contains 800-900 g/L of sugar. So… you can imagine how sweet this really is! The good news is that the Total acidity came in at 15.5 g/L, so I’m hoping that this will help balance the finished wine.

The problem with a wine containing 70% sugar is that the osmotic pressure is too great for most yeast to undergo fermentation. They find it difficult to transport waste across their cell membrane, so they die. There is one wine that I know of with an equivalent sugar content to what we achieved with this Frontenac Gris: Tokaji Essencia. This is a legendary Hungarian wine made from the juice that drips from dried, botyritis-infected berries. So, essentially, the free-run from botryitised raisins (if that makes sense). It has been known to reach 85% sugar in some years, but normally ranges from 50-70%. The other interesting thing about Essencia is that it can take 6-8 YEARS to ferment, and only obtains up to about 6% alcohol.

So, since I didn’t want to wait years to see what the final wine will taste like, nor did I want a wine with only 6% alcohol, I decided to add back a little bit of water to my Frontenac Gris. I brought it down to a still very respectable 45 Brix.

I started fermentation using a modified  pied de cuve method. I re-hydrated the yeast as one would normally do, but I used a larger quantity of water (I used 600 mL – the quantity I needed to dilute the wine to 45 brix). Then, I slowly added the syrupy goodness of the juice over a period of 24 hours. This allowed the yeast to slowly acclimate to their new (very harsh) environment, and ensured that my initial population of yeast was high. I used DV10 yeast because I know it’s pretty resistant (and it was on-hand). I would have preferred to use a yeast that is specifically made for ice wine/late harvest, but didn’t feel justified in ordering a whole package of yeast for this small quantity of wine. It seems to be fermenting nicely, regardless. I wonder how long it will take to finish… I’m excited to try it!

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…

Terroir and Minnesota

I recently spoke on the notion of terroir and how it relates to Minnesota during the annual Minnesota Grape Growers Association (MGGA) meeting this past weekend. It is one of my favorite subjects when talking about wine, as this concept is what first brought me into the wine world, and what ultimately brought me back to Minnesota and our developing wine industry. The concept of terroir means that wines from a particular region are unique, and incapable of being reproduced outside that area, even if the grape variety and winemaking techniques are duplicated. When defining terroir, most people talk about how the geography and the soil relate to the taste of an agricultural product – in our case, wine. There is good reason for this, as the word terroir has its roots in the french word terre, which means earth/soil. However, the word terroir is much more complex, as it involves an interactive ecosystem between the climate, soil, geography, as well as all the aspects of human intervention with this environment.
Domaine Romaneé-Conti Grand Cru

As wine is an historical beverage that dates back to at least 6000 B.C., its development over time has close ties with human history. We know that early-on in wine history people recognized that wine coming from different vineyard sites had different properties. The Romans would stamp clay amphorae with the wine’s region of origin, and Benedictine and Cistercian monks in the middle ages dedicated much of their time to determining the best vineyard sites to make their wine. Their boundaries still exist today in the Grand Cru vineyards in Burgundy. A wine-grower in Burgundy will never say they make a Pinot Noir from Burgundy, but rather that they make a Burgundian wine from Pinot Noir. Though it seems like simple semantics, the difference between these two statements is actually quite substantial. To distinguish what makes them different gets to the very heart of trying to define the concept of terroir.

You see, a terroir is more than just a geographical place with geological and climatic influence. It also includes the types of vines that were planted, how they are planted, and every aspect of farming that goes into making the grapes as well as every aspect of vinification. The history of the place and even the way the wine fits into the local culture is important. When defining whether an agriculture product has terroir, the Institut National des Appellations d’Origine (the branch of government that regulates the A.O.C. system of the Agriculture department in France) uses the following definition:

A delimited geographical area defined from a human community who built over the course of its history a set of distinctive cultural traits, knowledge, and practices based on a system of interactions between the natural environment and human factors. The craftsmanship in play reveals originality, gives a standard, and permits recognition of products or services originating in this space and thus for the people who live there.

Thus, terroir is as much about the culture and history of the people who live in a place as it is the factors of the natural environment. Which, raises the question of whether it is possible to have a true terroir in Minnesota. We have a burgeoning wine industry where, in 2007, two-thirds of the vineyards planted in the state were less than 4 years old. We have 10 major varieties that are being planted, and generally have no consistency in style for the wines made with these varieties. Most wineries source fruit from many different vineyard locations across the state, and often across the country to create blends that do little to show the typicality of a certain area. Although I realize that there are socio-economic factors driving this decision to buy out-of-state fruit, the very fact that wineries themselves aren’t embracing the notion of terroir means that we will never achieve it in our state.
One may ask why this matters – who really cares if our wines come from grapes grown in the state or not? As long as the wine is good, right? In the short run, making “branded” wines or vin d’effort (wines which owe all their characteristics to the effort of the winemaker rather than terroir), may prove successful for a variety of reasons. However, history has proven that the wine industry is boom and bust, and in the long run terroir wines end up surviving.


Take the example of the area around La Rochelle, France. During the middle ages, it had a booming wine industry. Located on the western coast of France, its harbor allowed for quick shipment of wine from France to Great Britain and Holland. Along with the nearby city of Bordeaux, it had access to a large consumer base, and a way to transport the wine to them. However, over time the economic significance of a port became less and less important. Environmental conditions (soil and climate) as well as the varieties chosen to cultivate in Bordeaux produced a wine of much higher quality. Thus, the wine industry in La Rochelle decreased with the decline of the port, while that of Bordeaux continued to flourish.

For one more example, I’ll point to the fact that the area around Paris had a booming wine industry in relatively recent times. In 1820, 4.8 million hectoliters of wine were being made from vineyards surrounding Paris. Compare that to the current production of 5.2 million hectoliters in Bordeaux, and one can see how significant this industry really was. Wineries around Paris had it easy: they had the largest consumer base in France right in their back yard. However, as soon as a railway was built linking Paris to Lyon and Marseille, it was possible to ship wine from the South of France to Paris. When phylloxera wiped out most of the vineyards in Europe, the vineyards around Paris were not replanted. Once again, vineyards planted where conditions favored high-quality wine production survived, while those that didn’t failed.
But what about regions where environment doesn’t favor the production of high-quality table wine? This is where the human factor comes in. I’ll point to the area of Champagne (just because it is the most well-known). It can be argued that the climate and soil of Champagne are not ideal for making wine. In fact, the vineyards of Champagne were at one time a garbage dump for much of Paris and Reims well into the 20th century. They were using the trash as compost. One can still walk the vineyards in Champagne and find bits of plastic and broken dishes in the soil. Its climate also makes it difficult to achieve optimum ripeness in grapes every year. Now, much has been written about the “invention” of Champagne, but the fact remains that the wine exists because the acidic, unripened fruit from these northerly vineyards makes hardly an ideal table wine. The cold winters made fermentation difficult, and re-fermentation in the bottle in springtime was normal in a time when sterile filtration and sulfur addition was non-existent. Eventually, small changes over time led to people purposefully allowing the wine to undergo a second fermentation in the bottle.  I realize this is a very simplistic discussion on the finer points of the history of this great wine, but the point is that this wine style developed because of decisions that a group of humans made based on their interactions with the surrounding environment. If it were only a single winery in Champagne that developed this style, I would argue that we wouldn’t associate the word “Champagne” with sparkling wine today. This emphasizes the importance of the human factor in the concept of terroir.
There are many examples throughout history that are all very interesting and intriguing, and I could go on (Hunter Valley Sémillon, New Zealand Sauvignon Blanc, Vin Jaune, Saint-Bris…) but as this post is possibly too long to contain the attention of the vast number of people reading it, I will try to come to a conclusion. Does Minnesota have a terroir? Not yet, maybe we never will. It is something that develops over time. How long, you ask? That is the most difficult question to answer. As we have seen, terroir develops when a group of people in a given area collectively decide to make wine in a certain style, using certain varieties, and certain viticultural and enological practices. I think the key word there is collectively. This will be a huge obstacle to overcome in Minnesota, as our culture was founded on individualism. Unlike Kantian philosophy that shaped continental Europe, we went the way of John Stuart Mill. We value our individual freedom, and believe we don’t have to adhere to general rules and principles. This sense of individualism is what drives innovation in our country. It is what, to some degree, makes us exceptional. It is also the driving force behind the Minnesota wine industry at present. However, I believe in the long-run, it may hinder our success in becoming a unique region. One of the keys to growth in our industry will be to garner acceptance within our community, and eventually in the wider market.  This, I believe, is possible. Because Minnesotans are very proud of our state, acceptance within Minnesota is easy. We love all things Minnesota. However we need to raise consistency and quality of the wines we produce to be accepted into the larger wine community. I’m hoping this blog is the start of a dialogue between growers and winemakers in Minnesota, as well as with the researchers at the University, so we may collectively advance our industry forward.