The Importance of pH in Wine Making

The Importance of pH in Wine Making

The pH of a wine is critical not only to its flavor but to nearly every aspect of the wine. According to wine maker Alison Crowe of Winemaker Magazine “pH is the backbone of a wine”. It is second in importance only to the must sugar levels. Fluctuations in pH could mean the difference between a wine going down the sink and one you hang a double gold medal on. What is pH exactly? The pH scale technically is a logarithmic scale that measures the concentration of free hydrogen ions floating around in your wine. The stronger the acid the more hydrogen ions you’ll have so in essence it is a measurement of how strong an acid is. The scale used to measure pH originally went from 0 to 14 with neutral fluids being at 7.0. Today, however, there are acids and bases that go beyond this scale. Acids have a pH less than 7.0 while bases have a pH higher than 7.0. Plain water measures 7.0. Most wines fall between 3.0 and 3.6. Young, unripe grapes have high acid levels. As the fruit ripens the acid levels decrease. An over ripe grape will have very low levels of acid. The trick for wine makers during harvest is choosing when to harvest the grape. They must harvest when the pH is at a satisfactory level but also as the grapes ripen the sugar, titratable acidity, and tannins are all also changing. So when to pick the grapes is based on when all these elements come into alignment to yield the best possible wine. In Technology of Winemaking the following pH ranges are recommended for wine musts: White Wines < 3.3 Red Wines < 3.4 Sweet Wines < 3.4 Dessert Wines < 3.6 This makes sense as white wines are generally better with higher acid (lower pH) and sweet dessert wines would necessarily have a lower acid (higher pH) due to the ripeness of the fruit at the time of pressing. How Does pH Affect My Wine? In essence it affects nearly every aspect of your wine. The pH affect flavor, aroma, color, tartrate precipitation, carbon dioxide absorption, malolactic fermentation, stability, ageablity, and fermentation rate. These are just a handful of the more noticeable affects. It can also affect the many chemical reactions that take place in a wine during and after fermentation. With the right acid level, which is subjective to a point, you can lock in flavors, aroma, a healthy color, and make sure your wine has good mouthfeel. Your fermentation will also go more smoothly. When the acid levels are too low your wine will lack body, the mouthfeel will be off, and it will taste weak or flabby. The wine can also pick up a brownish hue. Equally important is its effect on stability. Most types of bacteria and a few types of fungi are quite unhappy at pH levels of 3.0 to 3.75. For a finished with this is great because it is a natural protection agains spoilage micro organisms. There are times though when being in this idea pH range can be a problem. For...

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Sur Lie Aging Explained

Sur Lie Aging Explained

What is Sur Lie Aging? Sur lie aging is the process of allowing a finished wine to continue to sit on the lees in order to extract flavors. Recently we explored the fact that there are two different types of lees. There are the grape lees (coming from the fruit) and the yeast lees (you guessed it, from the yeast). Each of these can be used in sur lie aging and each will produce different results. Aging wine on the grape lees is something to be undertaken with extreme care as this lees can easily spoil a wine if not done properly. When done correctly though it can lead to a wonderfully complex wine. Yeast lees on the other hand is the more common lees to perform sur lie aging with. As the yeast decomposes it can impart nut, bread, and yeast flavors to a wine. Different yeast cells can contribute different flavors too so you’re not guaranteed to get the same thing from all yeast strains. The remainder of this article pertains to aging on the fine lees only. How does Sur Lie Aging Work? During sur lie the lees cells break down (i.e. decompose) into simpler compounds. This releases sugars and proteins that interact with the wine chemistry. There are also flavor and aroma compounds that get released. As the proteins are released they bind with tannins in the wine. This is good for a white wine as you don’t want tannins in a white. However, for a red wine this can be problematic as it is the tannins that go a long way in determining the aging potential of the wine. For this reason red wines are usually not aged this way while white wines often are. The deciding factor depends upon the intentions of the wine maker. If the lees are left undisturbed in the bottom of your aging vessel for too long they can start to form some nasty sulfur flavors and aromas. To keep this from happening you need to stir the lees regularly, a process called battonage. Stirring the lees keeps hydrogen sulfide from forming as quickly and ensures that your wine gets maximum exposure to the cells and the compounds they’re decomposing into. Things to Watch Out For As you proceed through the sur lie process be sure to pay special attention to the flavor profiles of your wine. You can over do this and end up with off flavors. If at any point you experience sulfur like flavors like rotten eggs, rack off the lees immediately. The sooner you take action the better your chances are of being able to deal with these off flavors. Taken too far and your wine won’t be drinkable. When to Age on The Lees Preparation for sur lie aging begins as fermentation is wrapping up. The lees should be stirred up every two to three days for the last bits of fermentation. Once fermentation has ended continue to stir the lees once or twice each week for a period of six weeks or so. After that stir it up monthly. Some wine makers prefer...

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Topping Up Your Wine

Topping Up Your Wine

The Importance of Topping Up While oxygen is necessary in the early stages of fermentation it is also the mortal enemy of wine makers once a wine has gone still. Topping up your wine after fermentation is complete is the best way to minimize how much oxygen your wine is exposed to. As our wines ferment we rack it from one container to another to get it off the lees. Each time we do this though we loose a bit of wine and increase the surface area of the wine we have left. This can leave us with too much head space at a time when our wine is most susceptible to oxygen exposure. Topping up is the process of adding wine to your carboy, barrel, or tank to reduce the amount of head space (also known as ullage). This serves two very important purposes. First, topping up reduces the amount of oxygen that gets trapped in your carboy or barrel after racking. Less oxygen means less oxidation. The second thing it does is reduce the surface area of your wine. Carboys get very narrow up at the neck just filling up a barrel also reduces the surface area. This is important because the free surface of your wine is the interface through which oxygen can interact with the rest of your wine. The smaller the free surface area of the wine is the more time it takes for your wine to become oxidized. This is especially important for small batches of wine. It takes much longer to oxidize wine in a carboy because the free surface area is so much smaller than it would be if left in a primary fermentation bucket. Topping up your carboy ensures that the free surface area is kept to a minimum. When to Top Up During primary fermentation we need that head space so that we have room for the foam that will form. Also, because the yeast is producing carbon dioxide in such huge amounts there’s little chance of oxygen getting to our wine. However, after primary fermentation carbon dioxide production decreases and is not enough to keep oxygen away from our wine. To protect our wine we attach airlocks or plugs but these are not fool proof and can let small amounts of oxygen in. To combat this we need to be topping up after primary fermentation ends. Note that wine kits do not have you top up until later in the wine making process which is fine as long as you stick to the time line laid out in the kit instructions. Winexpert has actually removed the topping up step from their instructions. Winemakers using oak barrels will experience much more evaporation because of the porous nature of oak. Also, because you can’t see how thick the lees is nor how deep your racking device is in the barrel a lot of wine gets left behind when racking. Thus topping up is critical when barrel aging wine. What to Top Up With Ideally when you make your wine you would have some in reserve to top up with. Wineries...

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The First Winemaker’s Academy Wine Tasting

The First Winemaker’s Academy Wine Tasting

The First Winemaker’s Academy Wine Tasting This past weekend (July 7th 2013) my wife and I hosted the very first wine tasting showcasing the wines produced during The Great Riesling Yeast Experiment (part i, part ii, part iii). It was held at our house with just one other couple we invited over. The point of this wine tasting, and the point of the experiment, was to determine if you could produce distinctly different wines by fermenting the same grape juice with different strains of yeast. I split a six gallon World Vineyard Riesling kit into two three gallon batches and fermented them separately, one with RHST and the other with W15 yeast strains. Setting The Stage The wine tasting was conducted blind so no one knew which Riesling was which. I didn’t want my wife or I to have any prejudgments based on previous bottles we had consumed. Because each bottle was labeled with the proportions of the blend it contained I had to cover the bottles. To do that I simply taped a sheet of printer paper around the bottle and gave it a number. Each taster had a place-mat with five glasses on it and the wines were poured in order from one to five. This way we would each be tasting the same wine at the same time and could share our thoughts along the way. The Wine Tasting We tasted each wine in turn taking the time to chat about what flavors we were picking up and how it came across. All five wines were identical in color which was not really surprising given that they came from the same grape juice. Between each wine we snacked on club style crackers to clear the palate. In hind sight I would have liked to have more pairing foods to go with the wines, however, more flavorful foods may have interfered with the objective of this experiment. The Results As the wine tasting progressed it became apparent that each of the five blends was in fact quite different from one another. Our guests, who are not wine fanatics like we are, commented that they definitely could tell a difference in the wines. The 100% W15 and 100% RSHT Rieslings of course showed the greatest difference in flavors as these were the unblended wines. In general if someone preferred the 100% W15 wine they also favored the blend that contained 75% W15 over the blend with only 25% W15. This was a great indicator that everyone could honestly tell the difference between each of the blends and there weren’t any issues playing with their perception. Some times during wine tastings your taste buds get worn out after a few wines and the later wines you drink all taste about the same. However, this was not a problem as indicated by the taster’s preferences. My wife liked the 75% W15 / 25% RHST blend the best while I preferred the 100% RHST. The husband of our guest couple preferred the 100% W15 and his wife also liked the 75% W15 / 25% RHST blend. So there was a bit of a spread between...

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Cold Stabilization of Wine

Cold Stabilization of Wine

What is Cold Stabilization? Cold stabilization of wine is a method used to keep tartaric acid crystals from forming after the wine as been bottled. This process is referred to as cold stabilization because it is the act of cooling the wine that causes tartaric acid to form tartrate crystals, also known as wine crystals or wine diamonds. If wines are not cold stabilized there is a chance that these crystals will form when consumers place bottles of wine in the refrigerator or store it for long periods of time. While the crystals are harmless it can be rather unsettling to find what looks like broken glass in your wine if you don’t know what it really is. Why do Tartrate Crystals Form? Tartaric acid is naturally present in wine making grapes so we can expect all grape wines to have it. However, after fermentation some wines will be supersaturated with tartaric acid, meaning that there is more tartaric acid in solution than what wine can naturally sustain. The excess tartaric acid will solidify and form crystals. This will continue until the acid reaches a concentration that can be sustained. When wines have this excess acid they are considered to be tartrate unstable. Things such as temperature changes, blending of wines, moving your wine around, and additives such as bentonite can cause the suspended acid to crystallize. Also, the higher your pH the higher your chances are of crystals forming Are Tartrate Crystals Harmful? No, tartrate crystals will not harm you if you happen to swallow a few. The only real hazard they pose is causing you to choke if you weren’t expecting chunks of stuff in your wine. In fact crushed tartrate crystals is the same thing as cream of tartar, yes the same stuff you have in your pantry right now. Wine barrels used to be a major industrial source of tartrate crystals for the production of cream of tartar. How to Cold Stabilize Wines Now that we understand how tartaric acid can lead to tartrate instabilities let’s talk about what we can do about it. The process is quite simple. Just reduce the temperature of your wine temperature to 30 degrees (F) or less for at least 36 hours. A spare refrigerator or a cold garage in the winter may be sufficiently cold to carry this process out. The warmer your wine is the longer this process will take though. To help things along you can optionally add potassium bitartrate powder which is merely small tartrate crystals. These additional crystals serve as seed crystals for the tartaric acid the bond to. This speeds up the crystallization process. While getting your wine down to 30 degrees (F) can help facilitate this process it’s not really cold enough to do a complete cold stabilization. Most amateur wine makers don’t have access to the sorts of equipment required to drop the temperature far enough to make wines their completely tartrate stable. Wineries use large cooling tanks where they can store huge amounts of wine and control the temperature very carefully. However, the process outlined above will still help you...

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How Oak Affects Wine

How Oak Affects Wine

Oak, also known as the winemakers spice cabinet. It affects wine not only the flavor of wine but its chemistry as well. It is important to understand that not all oak is the same. Different Oaks for Different Folks I’m sorry I couldn’t resist that. It is true though. Oak from different countries impart different flavors and textures to the wine it comes in contact with. This is why you see French and American barrels and oak chips at wine making shops. The two most popular types are French and American, however, there are many other places that supply winemakers as well. Hungary is one of the more popular ones outside the U.S. and France. French oak is more tame and subtle while American oak, like Americans, tend to be pretty bold. To be more specific, French oak has a finer grain with smaller voids (air space). This keeps the wine from penetrating very deeply into the oak thus reducing the surface area that the wine has contact with. This results in a smoother, subtle oak flavor. American oak, on the other hand has a looser grain that allows more interaction with the wine as it can penetrate deeper into that grain. Increased surface area allows for more extraction of flavors and tannins from the oak. Here are the four main impacts oak can have on wine. As you’ll see oak flavor is only one of the four. Evaporation The average 59 gallon barrel allows 5.5-6.5 gallons of wine evaporate per year. This is why wineries have to top up their barrels so much and why they smell so good! As wine evaporates is the water and alcohol that are lost, this concentrates the flavors and aromas. The water and alcohol that is lost is replaced with additional wine which introduces more flavor and aroma compounds. You can see how this would add up, especially for a red wine that is barrel aged for three years. Micro-Oxygenation This is a big one. Just as the barrels allow water and alcohol to evaporate out of the barrel, oxygen is also allowed in. However, only in very small quantities. While too much oxygen is obviously a bad thing the tiny amounts gained through micro-oxygenation is just enough to help the wine mature. Without this additional oxygen the wine can still mature, however, it takes much much longer to achieve similar results. Phenol Interaction Phenols are compounds found in the grape and the oak that make up the flavor, aroma, and mouthfeel of a wine. There are hundreds of different phenols in a typical wine. Most come from the grapes but oak can also impart some of its own. These phenols can combine to form new flavor and aroma compounds. One common compound created is vanillin which, as you might have guessed, gives wines a vanilla flavor. Fermenting wine in the barrel, or with oak chips, can also give rise to new compounds or at least modified compounds. As the yeast work their magic they process phenols from the grape juice and the oak, combining them to form new compounds, i.e. new flavors and aromas...

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