A whole lot is put into the scoring of wines. Some of the more reputable wine magazines hire people full time to travel to different wineries and taste their wines. but what does a score really mean? What does a best value wine really correspond to? It is mind boggling that a publication will score hundreds of the same varietal, but name a wine that is not the highest scoring and cheapest their 'best value wine.' It seems to me that there must be something else at play.
I am not here to speculate on why, but I am pretty opinionated when it comes to scoring. My attitude? I could care less (until we score a 98, then who knows :)). To me, scoring builds on the enigma and aristocratic cloak surrounding wine. Wine should not be intimidating, it should be something shared and expressed. At the core of winemaking is the desire to make the best wine possible and have the wine enjoyed, and the drinker should never forget that. They should follow their own tastes and smells and let that be the guide to what they enjoy, not the opinions of a few people who may have other vested interests in the industry.
And take it from me, I was very intimidated the first time I stepped in a winery. I was so worried about looking foolish that I was afraid to speak my mind. I will never forget the first time I was invited to taste with winemakers at the end of our day. Instead of talking with the winemakers and comparing what I was perceiving and thinking, I wrote everything down in a journal. Even though I had been working in cellars for a few years at that point, and a few years with those winemakers, I was still nervous about getting laughed out of the room. Or worse, to deflate their confidence in me as a budding winemaker. But wouldn't you know it, everything I wrote down jived with what they were thinking. It slowly began to dawn on me that they were just as interested in my opinions as I was theirs; after all their average consumer is not a winemaker, it was someone roughly like me. And it isn't that hard to pick out a bad wine from a good one, as long as a wine is free from obvious flaws then your opinion will be accepted, and you may find that wine people are much more open to discussing their product than you thought.
So please, don't be intimidated and don't let scores be your only guide. You are equipped with a very efficient machine for tasting wine, your 5 senses (ok, 4). They will not let you down, and don't forget that a wine is meant to be enjoyed, not scored. So if you enjoy it, don't worry about the score!
Sunday, September 4, 2011
Legs for Days
Legs. Can't take it anymore. They don't mean anything. I find some inexperienced wine drinkers asking me about legs in wine, and proclaiming how nice the legs of a particular wine are . There is a general lack of understanding about what causes this phenomenon in wine. It has nothing to do with anything but the alcohol and water, and the interactions between the two of them.
Liquids have surface tension. Water has significant surface tension, if you don't believe me belly flop into the next pool you see. Did it hurt? Of course it did, and the fact that it did demonstrates one of the most significant facts about water; hydrogen bonding. There is a high amount of intermolecular forces at play within a solution of one or more chemicals. Have you ever paused to wonder why water, with its low molecular weight, boils at such a high temperature? Take methanol, which is water with a methyl (CH3-) group in place of one of the hydrogen atoms. It boils at ~64C, even though intuition (higher molecular weight) would seem to point towards the opposite. Again, we can attribute that to hydrogen bonding.
Hydrogen bonding comes about due to locally induced polarity on the water molecule. Oxygen is a very electronegative element, it strongly attracts clouds of negative charge towards it. When oxygen is bonded with two hydrogen atoms, as in water, it begins to draw electron density towards itself, creating a local negative charge centered on the oxygen atom. This causes a local positive charge to show on each of the hydrogen atoms. When the hydrogen local positive charge finds the oxygen local negative charge, a slight attraction occurs. The sum of all of these individual attractions between the molecules is what causes water to act the way it does. When ethanol is added to the mixture, we see a boiling point depression. Simply put, the water is not as attracted to itself because the large methyl groups block direct hydrogen bonding for a certain percentage of water molecules thus reducing the net sum of the intermolecular forces. This affects the surface tension of water. It also begins to give us a picture of what actually might be responsible for legs in wine.
There are several physical characteristics at play when a glass of wine is swirled. The capillary effect, just like a paper towel absorbing water, causes the wine at the utmost top of the glass to stick to the glass and sheet out until its surface area is maximized. All of the surface area of the water/ethanol mixture leads to evaporation. Because alcohol has significantly higher vapor pressure, it begins to evaporate much faster than the water. As the concentration of alcohol decreases, the surface tension of water increases. This draws more wine up along the side of the glass, but this wine has reduced surface tension and cannot easily mix with the reduced alcohol (higher surface tension) liquid it is heading towards. This causes the wine to bead up and drop back into the glass. This is a demonstration of the Gibbs-Marangoni effect, essentially describing liquid flow between two or more liquids of different surface tension.
Now for the try-at-home test....
Anyone who doesn't buy this explanation should try three simple experiments at home. First, swirl your usual wine glass and place your hand over the top to stop evaporation. You will see that legs do not form if the alcohol cannot rapidly evaporate. Second, buy yourself a bottle of grain alcohol. Put some water in the sink and then place a drop of everclear in the center of the water. Water will rapidly flow away from the everclear, demonstrating surface tension gradient flow. Third, mix the everclear with some water and swirl it in a wine glass. See the legs? This should debunk anyone still holding on to the notion that legs in wine are an indicator of sweetness or fruit quality.
Liquids have surface tension. Water has significant surface tension, if you don't believe me belly flop into the next pool you see. Did it hurt? Of course it did, and the fact that it did demonstrates one of the most significant facts about water; hydrogen bonding. There is a high amount of intermolecular forces at play within a solution of one or more chemicals. Have you ever paused to wonder why water, with its low molecular weight, boils at such a high temperature? Take methanol, which is water with a methyl (CH3-) group in place of one of the hydrogen atoms. It boils at ~64C, even though intuition (higher molecular weight) would seem to point towards the opposite. Again, we can attribute that to hydrogen bonding.
Hydrogen bonding comes about due to locally induced polarity on the water molecule. Oxygen is a very electronegative element, it strongly attracts clouds of negative charge towards it. When oxygen is bonded with two hydrogen atoms, as in water, it begins to draw electron density towards itself, creating a local negative charge centered on the oxygen atom. This causes a local positive charge to show on each of the hydrogen atoms. When the hydrogen local positive charge finds the oxygen local negative charge, a slight attraction occurs. The sum of all of these individual attractions between the molecules is what causes water to act the way it does. When ethanol is added to the mixture, we see a boiling point depression. Simply put, the water is not as attracted to itself because the large methyl groups block direct hydrogen bonding for a certain percentage of water molecules thus reducing the net sum of the intermolecular forces. This affects the surface tension of water. It also begins to give us a picture of what actually might be responsible for legs in wine.
There are several physical characteristics at play when a glass of wine is swirled. The capillary effect, just like a paper towel absorbing water, causes the wine at the utmost top of the glass to stick to the glass and sheet out until its surface area is maximized. All of the surface area of the water/ethanol mixture leads to evaporation. Because alcohol has significantly higher vapor pressure, it begins to evaporate much faster than the water. As the concentration of alcohol decreases, the surface tension of water increases. This draws more wine up along the side of the glass, but this wine has reduced surface tension and cannot easily mix with the reduced alcohol (higher surface tension) liquid it is heading towards. This causes the wine to bead up and drop back into the glass. This is a demonstration of the Gibbs-Marangoni effect, essentially describing liquid flow between two or more liquids of different surface tension.
Now for the try-at-home test....
Anyone who doesn't buy this explanation should try three simple experiments at home. First, swirl your usual wine glass and place your hand over the top to stop evaporation. You will see that legs do not form if the alcohol cannot rapidly evaporate. Second, buy yourself a bottle of grain alcohol. Put some water in the sink and then place a drop of everclear in the center of the water. Water will rapidly flow away from the everclear, demonstrating surface tension gradient flow. Third, mix the everclear with some water and swirl it in a wine glass. See the legs? This should debunk anyone still holding on to the notion that legs in wine are an indicator of sweetness or fruit quality.
Harvest is coming...
It's looking like another close year in Oregon. With our second slow start up to the growing season in a row, I am beginning to have my doubts that the state will become 100% ripe. Right now we are anxiously watching the forecast, hoping for the best weather possible between now and Halloween. Some of the higher elevation sites have got to be feeling the crunch, harvest typically starts in a month or less. However, if 2010 taught me one thing, it is that wet years can lead to good wine. We made some excellent wine out of some horrible grapes last year, and if need be we will do it again. While the weather in Oregon may be less than desirable, it is a constant and something we must all learn to deal with. Hopefully we took some notes last year....
Monday, August 22, 2011
Oregon: A Refuge from Over Ripening
Ok so the title of this post is obviously sarcasm, but there is some truth to it. Especially in the Willamette Valley. Wine grape growing in Oregon is a challenge. The single biggest factor to affect the quality of the wine is the quality of the grapes in it. It is an often repeated saying, but good wine is made in the vineyard. That is not to put the entirety of the growing season on the vineyard manager though, weather is what determines the baseline of a growing season. Not everyone in Oregon will choose to use organic chemicals, or to machine harvest, but every region will be subjected to similar weather patterns. Freezing in April, rain in July, rot in October, these are all things that can and will happen to event the most manicured vineyard.
Winemakers typically track 4 things during maturation of grapes; the pH, titratable acidity, degrees Brix, and eventually the taste and feel of the berry. The challenge in Oregon winemaking and grape growing is hitting your picking window perfectly. A grapevine is intentionally stressed, a lot of vineyards in Oregon choose not to irrigate and instead let the taproots do the work. This is because the happiest grapevine is not necessarily the best wine producing one. The plant must be scared into thinking conditions aren't ideal and reproduction is a necessity. This causes a very thirsty plant by the end of ripening.
Winemakers must base there pick time off three factors, physical ripeness, crushing schedule (big wineries must sometimes pick early or late simply because they have no other time to process the fruit), and weather. No one wants the weather to determine the pick time because then the winemaker is out of control and must begin to gamble. Will more rain come? The second rain hits the ground it is absorbed by the vine and sugar and acidity levels begin to dilute. This will set off a chain reaction of actions and decisions which are designed to mitigate the fact that we live in a very hard place to grow grapes.
Why would dropping sugar levels be concerning to a winemaker? Yeast ferment sugars into carbon dioxide and ethanol, less sugar means less alcohol, more sugar means more alcohol. We try and achieve a balance between acid, sweetness, and bitterness in the wine. Bitterness can be controlled by the alcohol level, and there is a base alcohol that needs to be present in order for the wine to taste like a wine. It is therefore essential that we achieve a minimum sugar concentration within the grape juice before it becomes wine.
This post is geared more towards American wine in general, so California must enter the discussion. Some of the more revered regions in California enjoy completely different weather patters. While our cool and mild climate is conducive to Pinots, the dry heat and long summers of California are great for bigger reds like Cab and Syrah. Californian winemakers have the opposite problem that we do: too much sun. This is reflected in laws about what can be added to grape must. In Oregon, it is legal to add sugar directly to the must the increase degrees Brix before fermentation. In California, they must do the opposite and dilute the must down to a more agreable level (both for the yeast and the consumer). Huge, ripe crops are almost a guarantee in California, and part of the reason that Napa vineyard land is some of the most expensive in the world.
So why does all of this matter?
I received a comment to a post talking about giving up on American wine due to our usual problem: too much excess. Over sweet, and high alcohol were some of the typical descriptors used to describe American wine, and that hurts. I do not feel that this problem is linked to American wine in general, just certain regions and certain techniques that have been glorified to a point of distaste. I also have faith in economics, if American wine was being held back by over ripening and excess sugars, the market should have naturally compensated. Perhaps it is beginning to?
In most of the regions in Oregon, 15% alcohol is simply not achievable in a normal year. Based on recent trends, we are more likely to be under ripe. This leads to a berry which is higher in acid and lower in sugar. Our pinot gris should have a sweetness to it, but what really drives it home with consumers is the well balanced acid. That is no accident, we use the tools, or terroir, that the region gives us. So if you are in search of a different style of wine, I would recommend looking at a different region. As the industry grows winemakers are trying to explore every possible climate and soil they can offer to their vines, and with some excellent results.
Winemakers typically track 4 things during maturation of grapes; the pH, titratable acidity, degrees Brix, and eventually the taste and feel of the berry. The challenge in Oregon winemaking and grape growing is hitting your picking window perfectly. A grapevine is intentionally stressed, a lot of vineyards in Oregon choose not to irrigate and instead let the taproots do the work. This is because the happiest grapevine is not necessarily the best wine producing one. The plant must be scared into thinking conditions aren't ideal and reproduction is a necessity. This causes a very thirsty plant by the end of ripening.
Winemakers must base there pick time off three factors, physical ripeness, crushing schedule (big wineries must sometimes pick early or late simply because they have no other time to process the fruit), and weather. No one wants the weather to determine the pick time because then the winemaker is out of control and must begin to gamble. Will more rain come? The second rain hits the ground it is absorbed by the vine and sugar and acidity levels begin to dilute. This will set off a chain reaction of actions and decisions which are designed to mitigate the fact that we live in a very hard place to grow grapes.
Why would dropping sugar levels be concerning to a winemaker? Yeast ferment sugars into carbon dioxide and ethanol, less sugar means less alcohol, more sugar means more alcohol. We try and achieve a balance between acid, sweetness, and bitterness in the wine. Bitterness can be controlled by the alcohol level, and there is a base alcohol that needs to be present in order for the wine to taste like a wine. It is therefore essential that we achieve a minimum sugar concentration within the grape juice before it becomes wine.
This post is geared more towards American wine in general, so California must enter the discussion. Some of the more revered regions in California enjoy completely different weather patters. While our cool and mild climate is conducive to Pinots, the dry heat and long summers of California are great for bigger reds like Cab and Syrah. Californian winemakers have the opposite problem that we do: too much sun. This is reflected in laws about what can be added to grape must. In Oregon, it is legal to add sugar directly to the must the increase degrees Brix before fermentation. In California, they must do the opposite and dilute the must down to a more agreable level (both for the yeast and the consumer). Huge, ripe crops are almost a guarantee in California, and part of the reason that Napa vineyard land is some of the most expensive in the world.
So why does all of this matter?
I received a comment to a post talking about giving up on American wine due to our usual problem: too much excess. Over sweet, and high alcohol were some of the typical descriptors used to describe American wine, and that hurts. I do not feel that this problem is linked to American wine in general, just certain regions and certain techniques that have been glorified to a point of distaste. I also have faith in economics, if American wine was being held back by over ripening and excess sugars, the market should have naturally compensated. Perhaps it is beginning to?
In most of the regions in Oregon, 15% alcohol is simply not achievable in a normal year. Based on recent trends, we are more likely to be under ripe. This leads to a berry which is higher in acid and lower in sugar. Our pinot gris should have a sweetness to it, but what really drives it home with consumers is the well balanced acid. That is no accident, we use the tools, or terroir, that the region gives us. So if you are in search of a different style of wine, I would recommend looking at a different region. As the industry grows winemakers are trying to explore every possible climate and soil they can offer to their vines, and with some excellent results.
Gone Country...
Sorry for the delay in posting, I found myself at the Willamette Country Music Festival this weekend and the 3G was too overloaded to write anything. I have plenty of ideas though, more to come...
Tuesday, August 16, 2011
The Ice Age is Over
If there is one machine that will truly make my life easier, it is the electrodialysis filter that will soon be showing up on our loading dock. This filter eliminates the cold stabilization process currently used to prepare wine for bottling. In large production facilities, it is essential to cold stabilize wine. Cold stabilization refers to the process of removing excess tartaric acid as its salt, potassium hydrogen tartrate (KHT). The acid crystal is considered undesirable in young wines by American consumers, and we make quite an effort to ensure the chance of them forming in a young bottled wine is removed.
At wine pH, most acids will be at least partially deprotonated. In other words, they will exchange a hydrogen with a molecule of water and temporarily be left with a negative charge. This process happens countless times per second, but averaged over time the negative charge is available for reaction. When a potassium ion, which is positively charged, meets the negative charge on the tartrate, a stable ionic bond is formed and the molecule precipitates (becomes solid). This happens naturally with aging, but there are ways to accelerate the process. The usual way takes advantage of solubility.
Temperature greatly affects solubility. As temperature falls, so does solubility. Temperature is related to molecular vibration, more simply the space created between molecules by like-charge repulsion. The majority of molecules in wine are water molecules, as they are cooled their vibration slows and they move closer together. This literally squeezes out molecules which are unable to fit between the lattice. Modern wineries use a glycol cooling system to lower wines below the freezing point of water and precipitate out KHT molecules to settle at the bottom of the tank. If they do not perform cold stability and bottle soon after harvest, tartaric acid crytals will appear in the wine bottle. Additionally, we add an excess of KHT to the tank once it has cooled to provide a substrate for additional KHT precipitation. The process takes somewhere around two weeks to a month, during which time thick ice coats form on the jackets used to cool the tank.
Once cold stability is confirmed through a lab conductivity test, the wine is ready for filtration. It cannot be allowed to warm before filtration or the KHT crystals will dissolve back into solution. Our method of choice is a crossflow filter. At 8 gallons per minute it can be quite a process to filter just our Pinot Noir, and during the summer it is taxing to chill large tanks to the necessary temperature. That is why I am so excited for our new technology.
ED filtering is not new, but it is still very expensive to get started. However, the savings start paying for it immediately. Electrodialysis filters use an electric charge coupled with ion selective filters to attract potassium ions out of the wine. By removing excess potassium ions and some tartaric acid ions, the wine not longer has the chemical potential to precipitate tartrates in the short term. It is inevitable that it will happen eventually, but the amount is usually small and at that point, desired by the consumer as a show of maturity.
The filter does not require the wine to be cooled, making it a huge power saver. The crossflow filter can be run at cellar temperature as well, which speeds it from 50-100%. The filter also allows us to cut down the time required to prepare a wine for bottling. At the speed we are expanding every second counts. To me, this machine made absolute sense as a purchase. It saves us money, time, lab analysis, and me getting hit in the head by falling ice jackets. Oh, and I might just sleep a little better this year too.
At wine pH, most acids will be at least partially deprotonated. In other words, they will exchange a hydrogen with a molecule of water and temporarily be left with a negative charge. This process happens countless times per second, but averaged over time the negative charge is available for reaction. When a potassium ion, which is positively charged, meets the negative charge on the tartrate, a stable ionic bond is formed and the molecule precipitates (becomes solid). This happens naturally with aging, but there are ways to accelerate the process. The usual way takes advantage of solubility.
Temperature greatly affects solubility. As temperature falls, so does solubility. Temperature is related to molecular vibration, more simply the space created between molecules by like-charge repulsion. The majority of molecules in wine are water molecules, as they are cooled their vibration slows and they move closer together. This literally squeezes out molecules which are unable to fit between the lattice. Modern wineries use a glycol cooling system to lower wines below the freezing point of water and precipitate out KHT molecules to settle at the bottom of the tank. If they do not perform cold stability and bottle soon after harvest, tartaric acid crytals will appear in the wine bottle. Additionally, we add an excess of KHT to the tank once it has cooled to provide a substrate for additional KHT precipitation. The process takes somewhere around two weeks to a month, during which time thick ice coats form on the jackets used to cool the tank.
Once cold stability is confirmed through a lab conductivity test, the wine is ready for filtration. It cannot be allowed to warm before filtration or the KHT crystals will dissolve back into solution. Our method of choice is a crossflow filter. At 8 gallons per minute it can be quite a process to filter just our Pinot Noir, and during the summer it is taxing to chill large tanks to the necessary temperature. That is why I am so excited for our new technology.
ED filtering is not new, but it is still very expensive to get started. However, the savings start paying for it immediately. Electrodialysis filters use an electric charge coupled with ion selective filters to attract potassium ions out of the wine. By removing excess potassium ions and some tartaric acid ions, the wine not longer has the chemical potential to precipitate tartrates in the short term. It is inevitable that it will happen eventually, but the amount is usually small and at that point, desired by the consumer as a show of maturity.
The filter does not require the wine to be cooled, making it a huge power saver. The crossflow filter can be run at cellar temperature as well, which speeds it from 50-100%. The filter also allows us to cut down the time required to prepare a wine for bottling. At the speed we are expanding every second counts. To me, this machine made absolute sense as a purchase. It saves us money, time, lab analysis, and me getting hit in the head by falling ice jackets. Oh, and I might just sleep a little better this year too.
Monday, August 15, 2011
Molecular Sulfur
One of the most valuable things I have learned since beginning work in the industry has been the importance of doing things today. Oxidation doesn't wait, Brett doesn't wait, and we as winemakers should not either. This should be a guiding principle for winemakers when it comes to the use of sulfites. I say sulfites, not sulfur dioxide, to emphasize something I run into in Oregon a lot. There is a general lack of knowledge about the role of sulfites and what is actually happening when we add sulfites to a wine.
One of my favorite litmus tests for new wineries and winemakers is asking about their sulfur program. I would love to report that I often learn new facts about how other wineries maintain sulfur levels, but it simply isn't true. While we may not have the capital and resources that some of the large California wineries have, I believe there is still no excuse to be lazy or ignorant when it comes to the knowledge and testing of sulfites. But astonishingly there are plenty of winemakers who seem to be.
If you take one thing away from this post, realize this. The effectiveness of sulfur dioxide is directly related to the concentration of sulfites and the pH of the wine. A good winemaker would never let a lab get away with reporting just a free sulfur number, the pH and free sulfur should always be reported together. Sulfites exist as three distinct compounds at wine pH (Ok, 2 unless you are majorly messing up). There is the very familiar molecular sulfur, SO2, bisulfite anion HSO3-, and the sulfite anion SO3=. At 0 pH it will exist as almost 100% molecular SO2. When the pH gets to ~4.5 the species is ~100% HSO3-. The behavior of HSO3-/SO3= is very similar.
A quick chemistry aside:
We chemists rely on changing the polarity of chemicals as a way to get them to elute from a solvent. The aeration-oxidation test for free sulfur takes advantage of this principle. By adding excess phosphoric acid the pH is driven down to maximize the amount of molecular SO2 present. Molecular SO2 is very volatile, while the deprotonated forms will not come out of water easily. In addition there is a very nice oxidation reaction that takes place between SO2 and H2O2, making the molecular form the most easy to capture and quantify. So what we are doing with aeration-oxidation is converting all of the sulfite species to molecular sulfur dioxide, eluting the mSO2 into peroxide, and then titrating. This is a very convenient way to measure the amount of molecular sulfur at an artificial (0) pH, but it tells us nothing about the amount of molecular sulfur at wine pH.
This is why the concerned winemaker should always ask for a pH. The most effective antimicrobial form of sulfite is molecular SO2. I have heard many different concentrations, but in general we keep wines in the cellar at 0.8 ppm molecular SO2. Bear in mind that we make a lot of cold climate Pinots, so our pH is usually below 3.55 or so. Our lowest is a Riesling clocking in at 2.95. To be adequately protected, the Riesling would be kept at 12 ppm free, and the 3.55 Pinot at 46 ppm free. This opens up a huge discussion on the winemaker's decisions around bottling, but that is a post for another day.
It is also worth nothing that pH can be a limiting factor for sulfur. A Cabernet with a pH of 3.80 simply will not drink well with 79 ppm free. However, that is no excuse to be lazy. One must lab trial and come up with a level that balances detectability with protection; having too much sulfur by 15 ppm is a lot easier to deal with then having to remedy early and excessive oxidation with the possibility of a host of spoilage organisms.
Chemicals are very valuable tools. SO2 is a wonder-chemical to a winemaker. Anti-oxidant, anti-oxidase, and anti-microbial; it is a perfect tool for the long and short term storage of wine. And when it is used correctly, the consumer will enjoy the wine exactly as it was intended. If there is anything valuable to be learned in this post, it is that fact. Good SO2 management makes good wine.
One of my favorite litmus tests for new wineries and winemakers is asking about their sulfur program. I would love to report that I often learn new facts about how other wineries maintain sulfur levels, but it simply isn't true. While we may not have the capital and resources that some of the large California wineries have, I believe there is still no excuse to be lazy or ignorant when it comes to the knowledge and testing of sulfites. But astonishingly there are plenty of winemakers who seem to be.
If you take one thing away from this post, realize this. The effectiveness of sulfur dioxide is directly related to the concentration of sulfites and the pH of the wine. A good winemaker would never let a lab get away with reporting just a free sulfur number, the pH and free sulfur should always be reported together. Sulfites exist as three distinct compounds at wine pH (Ok, 2 unless you are majorly messing up). There is the very familiar molecular sulfur, SO2, bisulfite anion HSO3-, and the sulfite anion SO3=. At 0 pH it will exist as almost 100% molecular SO2. When the pH gets to ~4.5 the species is ~100% HSO3-. The behavior of HSO3-/SO3= is very similar.
A quick chemistry aside:
We chemists rely on changing the polarity of chemicals as a way to get them to elute from a solvent. The aeration-oxidation test for free sulfur takes advantage of this principle. By adding excess phosphoric acid the pH is driven down to maximize the amount of molecular SO2 present. Molecular SO2 is very volatile, while the deprotonated forms will not come out of water easily. In addition there is a very nice oxidation reaction that takes place between SO2 and H2O2, making the molecular form the most easy to capture and quantify. So what we are doing with aeration-oxidation is converting all of the sulfite species to molecular sulfur dioxide, eluting the mSO2 into peroxide, and then titrating. This is a very convenient way to measure the amount of molecular sulfur at an artificial (0) pH, but it tells us nothing about the amount of molecular sulfur at wine pH.
This is why the concerned winemaker should always ask for a pH. The most effective antimicrobial form of sulfite is molecular SO2. I have heard many different concentrations, but in general we keep wines in the cellar at 0.8 ppm molecular SO2. Bear in mind that we make a lot of cold climate Pinots, so our pH is usually below 3.55 or so. Our lowest is a Riesling clocking in at 2.95. To be adequately protected, the Riesling would be kept at 12 ppm free, and the 3.55 Pinot at 46 ppm free. This opens up a huge discussion on the winemaker's decisions around bottling, but that is a post for another day.
It is also worth nothing that pH can be a limiting factor for sulfur. A Cabernet with a pH of 3.80 simply will not drink well with 79 ppm free. However, that is no excuse to be lazy. One must lab trial and come up with a level that balances detectability with protection; having too much sulfur by 15 ppm is a lot easier to deal with then having to remedy early and excessive oxidation with the possibility of a host of spoilage organisms.
Chemicals are very valuable tools. SO2 is a wonder-chemical to a winemaker. Anti-oxidant, anti-oxidase, and anti-microbial; it is a perfect tool for the long and short term storage of wine. And when it is used correctly, the consumer will enjoy the wine exactly as it was intended. If there is anything valuable to be learned in this post, it is that fact. Good SO2 management makes good wine.
Subscribe to:
Posts (Atom)