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 | ||||||
Measuring Sugar in wine
Learning how to measure sugar in your grapes, juice, and wine is the most fundamental analysis that winemakers learn. It is sugar that will be converted to alcohol by your yeast, so an accurate measurement in the vineyard and in the juice or must at harvest can give you a good estimate of your wine’s potential alcohol. It is rarely the case that your wine will have too little alcohol – early harvest Riesling in Germany often has final alcohol levels between 7 and 10%. Even with alcohol levels this low, the wine’s low pH helps to keep it stable against microbes. Proper sanitation through the vinification process will ensure a clean and crisp wine. If your potential alcohol is too high, on the other hand (> 14%), your fermentation may struggle towards the end, depending on the type of yeast involved.
Refractometer
The first tool often used to measure sugar is a refractometer. I won’t go into too much detail on it’s use as it’s pretty straightforward. A drop of juice is placed on a quartz surface at one end of the instrument, and you look through the sight glass on the other end. The sugar in the juice will cause light to bend at a certain angle, depending on the quantity. The refractometer measures this angle and contains a scale corresponding the the quantity of dissolved sugar in the mixture. The scale is typically given in °Brix measurement (% sucrose by mass – ie grams sucrose/100 g of solution). It is important to realize that this tool will only give you an accurate measure of your sugar when used in juice. Once your wine starts fermenting, any reading will be inaccurate due to the fact that alcohol has a higher refractive index than water. If there is any alcohol present when using a refractometer, your brix reading will be artificially high. On more than one occasion, a winemaker will discuss their vinification process with me using the term “brix.” Often it’s used when discussing residual sugars in their wines, or perhaps the level of sugar remaining when the wine was pressed. This always causes me to cringe a bit inside, because I know that if they are using Brix to measure remaining sugar in their wine, there is no doubt that the measurement is incorrect.
Once fermentation begins, a hydrometer should be used to measure the specific gravity of your wine. Often hydrometers come with more than one scale on the side. Many times, there is a scale used to measure Brix. Again, °Brix is a measurement of the percentage of sugar by weight in your solution. Because alcohol weighs less than water, measuring your °Brix by specific gravity will give you an incorrect measurement of the actual amount of remaining sugar if there is alcohol in the solution. A hydrometer is not capable of determining the amount of alcohol present in a solution. So, depending on the sugar you started with, the percentage of alcohol can vary by a few degrees with the same quantity of sugar remaining. If alcohol is present when you measure °Brix by specific gravity, the number you get for your brix measurement will be lower than it actually is. If you have a hydrometer with a Brix scale, it should only be used when measuring the sugar quantity in grape juice. You should not be using it to track the fermentation of your wine.
During fermentation, one should use the hydrometer’s specific gravity scale. Tracking your specific gravity will help you determine how quickly the sugar in your wine is being converted into alcohol. All hydrometers are calibrated at 20°C, so you should also measure the temperature of your wine and correct your specific gravity based on the temperature. Your hydrometer should come with a temperature correction chart. Take your reading by looking at the bottom of the meniscus and line it up with the corresponding numbers on the scale. Another common error is measuring a must that contains lots of particles of skins or pulp. This will interfere with your measurement. Carbon dioxide can also push the hydrometer up in your graduated cylinder, so be sure to take your reading quickly if your wine is fermenting.
Once the s.g. falls below 1.0, you know that there is less sugar in the wine than alcohol. It DOES NOT mean that your wine is now “dry,” but it is getting close to dryness. This is another mistake that I’ve come across over and over again. I’ve had people come to me wondering why their wine started re-fermenting in the bottle. They insist that the wine was dry when they bottled it, and when I ask how they measured the residual sugar I’m told that the specific gravity was less than 1.0. Remember that the specific gravity is the result of a mixture of mainly water, alcohol, and sugar. If your alcohol is very high, you can still have quite a bit of residual sugar left in your wine and still have the s.g. fall below one. In most cases, there is still 2% residual sugar – a sufficient quantity to cause re-fermentation at a later date. Another serious issue is starting malolactic fermentation (MLF) with this much residual sugar. The bacteria responsible for the conversion of malic acid to lactic acid also love to munch on sugar (like most any living creature). The problem is, unlike yeast, bacteria will convert sugar to acetic acid, which increases the wine’s volatile acidity. Thus if you have a wine destined to undergo MLF, you should be certain that it is dry.
Once the specific gravity drops below 1.0, another test is needed to measure residual sugar. Many home winemakers use Clinitest for this purpose. Some commercial winemakers may also use it as a quick way to estimate remaining sugar in the wine. It was once an important tool used to measure residual sugar in the urine of diabetics. It is a fairly simple test: a few drops of wine are placed in a test tube with a tablet that reacts strongly with the liquid. The tablet’s reaction with the sugar causes a color change that is then compared with a standard color strip that indicates the percent of sugar in the solution. The downside of Clinitest is that it can be difficult to measure the color change in red wines. Also, because an eye-dropper is used to measure your wine sample, you cannot count on your results to be accurate. It is a good idea to run the test several times so you can be confident in your results. Wine with a residual Sugar that is < 0.5% can be considered dry. It is rare for a wine to have zero sugar at the end of fermentation.
If you have access to a spectrophotometer, enzymatic analysis of residual sugar is one of the best and most accurate ways to determine the quantity of sugar left in your wine. When sending a sample to a lab for analysis, this is likely the method that they use. I highly recommend that any winery interested in doing their own lab analysis invest in a spectrophotometer. It is one of the most important pieced of equipment for wine analysis. Click the link above to get a great article from Cornell University on the many uses of a spectrophotometer. A basic model for wine and juice analysis can be purchased for less than $1000, and will open the door to a whole new range of testing capabilities.
It’s Snowing… in my bottle!
I recently had a few wineries who brought me examples of bottles of wine that resembled snow globes. Though I realize that Minnesotans are missing snow this winter, I doubt that seeing it in a bottle of wine will make up for it! Haze formation or deposits in wine are caused by the wine not being properly stabilized, and are quite varied in origin.
I had to brush-up on my detective skills on how to identify each different type of deposit, and thought I’d share them with you. I imagine that this problem might be more widespread than the examples I received this week.
I can’t stress the importance of stability testing before bottling your wines. Though “stability” is a fairly obscure term, in general, a wine that is stable would be expected not to undergo any undesirable physical or sensory changes from the time of bottling until it is consumed. Although it is impossible for a winemaker to imagine what the life of each particular bottle of wine will have or the conditions it will be exposed to, a series of stability tests have been devised that will predict physical changes to the wine throughout typical wine storage.
Stability tests are carried out pre-bottling in order to predict protein stability, tartrate stability, oxidative stability, color stability, and metal stability. It is important to learn more about the causes of each of these instability problems in order to prevent them from occurring in your wine. However, small wineries or home winemakers sometimes overlook the importance of doing these stability tests – not realizing their wine is unstable until a deposit forms in the bottle. Yes, I know they are time-consuming and tedious, but once a deposit forms in your wine there is really little you can do but decant each bottle, filter out the deposit, and re-bottle the wine (after having to do it on a few hundred bottles of wine, you will perhaps realize that stability testing isn’t a waste of time after all). However, understanding the source of the deposit may help you understand the underlying cause so that you can prevent the problem in the future.
Perhaps the easiest type of deposit to identify are crystalline deposits. These are either Potassium tartrate crystals or Calcium tartrate crystals. If the latter, the crystal may appear in a more rhomboid shape. However, the only real way to determine what mineral is involved is by a flame test. Calcium burns red, while potassium will burn violet.
The amorphous (or non-crystalline) deposits that form in wine are a bit more difficult to differentiate. There are four different origins of these amorphous deposits: proteins, tannins/pigments, mineral (copper or iron), or microbiological.
Protein precipitation is perhaps the most common cause of a hazy deposit. It’s typically light (white to tan) in color and consists of very fine particles that remain in suspension for a long period of time. To be sure, if you are able to collect the deposit by either decanting the wine or by centrifugation, then try to dissolve it in a 0.1 M sodium hydroxide (NaOH) solution. If it dissolves, it is likely protein in origin.
If the deposit is due to tannin and/or pigment precipitation, the color of the deposit will often be darker in color – more brownish than white. If you can collect the deposit, it should be soluble in a 50% ethanol solution. The source of this deposit is often due to oxidation of some of the pigments in the wine. However, it is also possible that if you overfined your wine with a protein fining agent, some of the excess protein can react with the tannins in natural cork closures when you bottle it. They will combine to form a precipitate in the bottle.
A haze that is microbial in origin will typically be accompanied by a wine that has excess carbon dioxide. It is fairly unmistakeable when a wine shows a bit of unintended fizz. Microorganisms (yeast and bacteria) are never the cause of protein instability in a wine. Haze due to microorganisms is usually due to improper filtration or sanitation of your bottling line. You can confirm this type of deposit by looking at it under a microscope.
Excess iron or copper can also form a deposit in your bottle. During bottling, exposure to oxygen causes iron to change from its soluble state to an insoluble state. In red wines, it interacts with the tannins to cause a precipitation that is blue in color. In white wines it interacts with phosphates. You need a significant quantity of excess iron for this reaction to occur – more than 7 mg/L for white wines, and more than 10 mg/L for red wines. Typically these levels are only obtained if a vineyard or winery uses old equipment constructed from iron. Another possible cause is if vineyard soils are treated with iron, and dust from the earth is somehow deposited on the grapes prior to harvest. Copper deposits are also rare, and form in conditions of reduction (opposite of oxidation) and are accelerated when the bottle is exposed to light. Again, this type of deposit is rare in modern winemaking. Older cellars might still have equipment made of brass, which can cause excess copper to form in the wine. Residual copper from vineyard sprays may also make their way into the winery if the spray was done too close to harvest. It’s also possible that when treating your wine with copper sulfate you added excess copper. If your wine contains more than 0.5 mg/L of residual copper, it should be treated with a protective colloid such as gum arabic. Note that the legal limit of residual copper in your wine is 1 mg/L. Thus, the importance of running bench trials prior to using copper sulfate to treat reduction odors! A deposit that is mineral in origin will dissolve in a solution of 25% hydrochloric acid (HCl).
Hopefully this short tutorial on identifying deposits in your wine will help with preventing them in the future!
Source:
Iland, P., N. Bruer, E. Wilkes. 2004. Chemical Analysis of Grapes and Wine: Techniques and Concepts. Patrick Iland Wine Promotions.
Comments