1. I have read that you need 1 million viable Oenococcus oeni cells / ml wine for malolactic conversion to begin. Is this true? If so, why?
Fermentation is a numbers game. With both Yeast and beneficial bacteria a critical number of organisms must exist to establish themselves amongst the many other microbes competing for a place in the must, or wine. Inoculation, or cultivation of one million (or 10e6 Colony-forming units (CFU)/ml) cells is a common recommendation for inoculation to ensure the bacteria can quickly establish themselves. Over the course of the malolactic fermentation, the population can rise to 10e9 CFU/ml or higher cells. Lower than 10e6 CFU/ml cells can still be effective however there is a greater risk of the bacteria not “taking” as well as there will be a longer period of time between inoculation and obtaining enough cells for ML conversion to take place at an acceptable speed.
2. what do most wineries do with their spent grapes after pressing?
First off: During the growing season fresh pomace and solids should be kept far away from the vineyard in order to reduce the habitat where fruit fly populations can develop and then reach later ripening varieties, as a means to minimize sour rot development.
Many wineries collect solids and pomace from the winery, then properly compost the pomace and spread it out back in the vineyard when harvest is complete. Another way wineries use there pomace is through feed farms where cows and pigs can eat the pomace, especially unfermented pomace. Large wineries also use pomace to produce other produces including grape seed oil, exogenous tannin products, food colorings, tartaric acid, and antimicrobial agents
3. How is oxygen both good and bad in winemaking depending on who you ask? What does micro oxygenation do?
This is a great question! Yes, oxygen can be a good thing at times and a very bad thing during the winemaking process
The good: At the start of alcoholic fermentation, yeast actually grow in the presence of oxygen and can produce a number of ATP molecules, sterols, and unsaturated fatty acids which are useful when alcoholic fermentation is actually going, but most importantly the total number of yeast increase which is the most effective way at reducing the chance of premature stoppage.
The bad: Once a wine is going through alcoholic fermentation, keeping oxygen away from the wine is ideal because oxygen can allow for spoilage organisms like Acetobacter aceti to grow and increase the volatile acidity in your wine. Also oxygen will oxidize aromatic and phenolic compounds, usually leading to low quality wines.
One of the exceptions to this is when a red wine has high concentrations of tannin which results in very astringent wines. One way to deal with big, aggressive tannins is to slowly expose them to oxygen which allows for tannins to become less astringent through a number of chemical reactions including polymerization and depolymerization along with copigmentation. This has traditionally been done in oak barrels, but with red wines made in stainless steel tanks, MOX devices where small doses of oxygen are slowly added to the wine (usually through an oxygen stone) have been made to mimic the effects of a barrel. Too much micro oxygenation then you can have oxidative breakdown of anthocyanins and the possibility of spoilage as well.
4. What is the best strategy in the winemaking process to promote the formation of complex anthocyanins?
Anthocyanins can interact with a number of compounds in wine, but the primary reaction is copigmentation. In short, copigmentation is the interaction of anthocyanins with different forms of anthocyanins or phenolic compounds (mainly tannins) though low energy bonds (hydrogen bonds and/or hydrophobic interactions). The reaction is promoted by higher temperatures and requires an acid medium (i.e. wine). The reaction product is a colorless compound and turns red when oxidized, then evolves to orange over time.
Factors that influence copigmentation include concentration of anthocyanins, type and quantity of phenolic compounds, pH, and temperature.
There are a lot of different thoughts on what should be done to promote copigmentation. The most important factor is having substrate (tannin and anthocyanin) for the reaction to occur. Also important is having ethanal (oxidative product of ethanol) which promotes copigmentation. Adding oxygen through barrel aging, micro-oxygenation, and/or racking will promote ethanal formation. It is important to not to add too much oxygen as this will result in the oxidation of anthocyanins and other important flavor compounds.
5. Can the solids from cuvée and taille juice be used to boost the quality of taille-made sparkling wine (if Champagne press fractions are used)?
First for those unfamiliar with the terms cuvée is the juice that first is pressed off when producing the base wine for sparkling wine production (in Champagne production this is the first 20.5hl/4,000kg of fruit or 123 gallons/Ton). The Taille is the following 5hl of juice pressed from the same fruit.
We are going to break this answer up into Champagne production and the rest of the world using “Champagne” methods:
1. Champagne- The basic answer is no as mixing cuvée into your taille fraction would be to dilute high value and just with that destined to be worth less. This is not to say that stylistically a winemaker could not make an excellent wine in this fashion but restrictions on labeling should be expected.
2. All wine- The first juice to come out of the press is relatively higher in sugar and tartaric acid then that which comes later in the press run. It also has a lower pH and lower potassium content. When trying to make a traditional base for a sparkling wine, the low pH and high acidity that comes from the wine early in the press run in generally desired. Increased pressing can however increase the release of aroma compounds such as monoterpenes and their glycosidically bound precursors. If pressing a variety known for this character, inclusion of later press fractions may be desired, however along with the aromas can come bitterness from other compounds.
5. What are the most popular chemicals that are applied to vineyards in the finger lakes?
Fungicides in general to combat 5 major diseases in the humid East. Listed in our NY/PA pest management guidelines.
6. Are there any vineyards in the finger lakes (in NY) that practice cultivation techniques that could qualify as carbon negative?
Current recommended best practices for vineyards generally encourage increased soil organic matter. This is commonly accomplished through little to no tillage, cover crops, additional of mulch and in some cases under vine cover. These practices will generally increase carbon sequestered in vineyards beyond what may have been historically accomplished. This however will not produce a carbon negative vineyard given all inputs but there are growers that take additional steps as well to offset their carbon footprint in the field and out. http://www.vinebalance.com/pdf/newsletters/SustainableViticulture2.pdf
7. What percentage of vineyards employ buffer strips/ riparian strips to control runoff from their fields?
In New York State Close to 100% - Because of our hillside vineyards and lakes, many growers have incorporated diversion ditches, seeded row middles and cover crops, and drainage. Here’s an article where it is all laid out: http://www.vinebalance.com/pdf/newsletters/SustainableViticulture2.pdf
8. What do most wineries do with their trimmings?
With disease free cuttings most use a brush hog to chop them up and leave them in row middles. Biomass returned to soil. There is the risk that some pathogens that can be carried over in this manner, so removal from the vineyard is ideal.
9. we have had pretty severe powdery mildew (PM) pressure this year. Harvest here will start in the next few weeks. Assuming one segregates the worst PM red grape clusters before they enter the crusher destemmer, at what level does the PM affect the wine? What is the answer for white grapes?
First: If you still have a few weeks make sure to do all you can to cleanup the fruit. Hydrogen peroxide (Oxidate), potassium bicarbonate salts and horticultural oils all have eradication activity. Though pay attention to pre-harvest intervals. Unfortunately, there has not been much research on the threshold of the amount of PM required to cause off aromas. Mushroom like off aromas, such as 1-octen-3one can be expected if the levels are exceeded (Darriet 2002).
For white wines you will want to clarify the juice as quickly as possible. Early fining with bentonite may help, or if you can tell that a mushroom like aroma is present you will want to experiment with early fining of the juice, elevating to activated charcoal in the worst cases. While not the option any winemaker wants to use It is better to start with a neutral juice than one that smells like mushrooms!
Unfortunately, with red wine making sorting is your best option as you need the skin contact, but the skin contact will also help pull out any of the unwanted PM aromas. Some potential options to save as much fruit as possible is to sort into excellent fruit that you know can make good wine and then other grades and ferment separately. You may find your second or third quality still gives you surprisingly good wine. Alternately, you may want to consider making a rosé out of the less desirable fruit to minimize skin contact.
Last in all cases do not try to do a "natural" fermentation. Along with the PM your fruit is teaming with lots of other undesirable microbes which can make your problem worse. Start with an appropriate dose of SO2 to knock everything back and then a yeast that you know will establish quickly and give you a nice clean fermentation.
10. I just harvest my Sauvignon blanc... everything went perfect and I got my juice into my little winery at 21 C...added pectinase and let it settle overnight...seems to have settled well, and I went to rack it with my little pump...and pump was dead...I have no way to elevate tank and syphon the settled juice... What do you think of the idea of going ahead with fermentation in the same tank?...will the lees be compact enough to allow fermentation...will take me 3 days to get another pump...what will happen to juice if I wAit 3 days
So I'd say you have two reasonable options:
1. Safest option: To avoid spoilage organisms which will give you off flavors and increased volatile acidity, you should just inoculate now with the lees which will likely produce a much different style then the typical California Sauvignon blanc (usually clean and crisp). With the lees you will probably get a "heavier" mouthfeel and different aromatic compounds plus your fermentation may be quicker, probably more similar to a barrel fermented Sauvignon Blanc.
2. To make a clean/crisp Sauvignon Blanc you could make a high SO2 addition (100 mg/l or more) and try to keep the tank as cool as possible to slow the start of fermentation and rack the wine asap once the pump arrives. Then inoculate with a higher than normal rate of yeast to overcome the higher SO2 levels and/or non-Saccharomyces yeast and bacteria.
11. If you want to lower alcohol content in wine, why is it better to add water to unfermented must than to the finished wine?
Yeast tend to produce increased levels of H2S and acetic acid when under high osmotic stress (i.e. too much sugar). Nearly all wine yeast are happy up to a must that would produce 13%ABV, to ferment above that you have to select carefully and as you approach 15-16% even the most robust yeast can have trouble.
Another reason also relates to the yeast, but in the desirable flavors they produce. While much of a wines aroma and mouthfeel comes from the grape, important aspects also come from the yeast. If you dilute your must first you are only diluting the grape flavors, if you dilute after you are diluting both the grape and fermentation derived flavors.
Finally, for red fermentations on the skins you will still extract more phenolic compounds (tannins and anthocyanins) at a lower alcohol level then if you were to dilute the wine after maceration. A common practice for this is to saignée the volume you need in order to dilute the juice to a reasonable Brix level and then add back water, so you still have the same juice volume to extract with, but your alcohol levels will be lower.
12. What is the conversion ratio of malic acid to lactic acid during MLF?
Assuming complete conversion for every mole of malate you will get 1 mole of lactate. So the short answer is 1:1 (with Co2 also produced). As with many things with wine the full implications can be a little more complicated. When measuring titratable acidity we calculate everything "as tartaric" meaning that the amount of NaOH needed to neutralize acids is calculated for the molecular weight of tartaric, and accounting for it is being "di-protic." Malic acid is also di-protic whereas lactic is monoprotic. In effect MLF in converting your malic to lactic will produce 0.5g/l "as tartaric" of lactic acid out of 1.0 g/l "as tartaric" of malic acid. To further complicate matters malic acid can also increase measurable acetic acid so while the enzymatic conversion rate of malic to lactic is very predictable the impact on MLF on titratable acidity is more complicated.
13. During the summer I ferment my homemade grape and fruit wines (5-20 gallon batches) in my garage where during the day the temperature gets up to 90-95F. Outside is hotter. My wine seems OK, but would it be better if I found a way to ferment at 70-75F ??
It depends on the volume and if it is red or white. That is way above what is "ideal" for a classic white fermentation as it will not promote the desired aroma and the high temps can increase phenolic solubilization from whatever grape matter was left in the must. However, that is not to say you cannot make an enjoyable white at higher temperatures. If it is a red wine, you are probably right in the range if you are fermenting in small fermentation vessels. Once you get above about 50 gallon the amount of heat the yeast generate is lower than what the vessel can dissipate, so you need active cooling to keep them alive.
14. When is the best time to add S02 to grapes or juice prior to fermentation?
The "safest" way to make wine is to add SO2 as soon as possible. Once they are harvested yeast will start fermenting the sugar that has been exposed. If it is not a yeast you chose and rather a wild yeast it could produce unwanted flavors. Some growers will actually add SO2 to the harvest bins to stop oxidation and inhibit yeast. After you dose your must or fruit you should wait about 24 hours before inoculation, otherwise you may also knock out your yeast. It is however possible to make wine without ever adding SO2, it just means incredible sanitation, acceptance of unpredictability and a little luck. If you adopt this model you need nice clean fruit and to keep on top of O2 management as any O2 entering the system will likely produce unwanted results after fermentation
15. I crushed approximately 1000 pounds of Primitivo last Wednesday. I checked Brix at 27 1/2 and pH 3.6. I add the potassium meta bisulfite. The next morning the Brix was at 28 1/2 and the pH 3.93 temp 61. I want the Brix at 26 and the pH at 3.4. So between Monday I added a total of 7 gallons of water and only 250 grams of tartaric acid. I that is way low on the amount I should add, I’m always afraid of too much. I added yeast and go-ferm and yeast yesterday. Today the Brix is at 26 1/2 and the pH 3.7. Can I still add tartaric acid after fermentation has just begun?
The short answer is that you can always add tartaric acid. In some cases, early additions can be favorable, especially if the must pH is excessively high. In other cases, you may want to wait until after ML to ensure it proceeds OK (you don’t want to have your wine below pH 3.5 before initiating ML). Now if you have gone through secondary and you either feel your wine needs grater acidity for a balanced palate or lower the pH you can still add tartaric, however the risk is that it may not stay in solution because it will bind with potassium and fall out. The good news is that you are actually solving your pH problem as removing the excess potassium will help drive your pH down, additionally you will usually find that if you add enough sacrificial tartaric, over time you will see more stay in solution. That is because for tartrate instability you need the cations you have been precipitating with your tartrate additions. Now in larger vinifications this repeated addition of tartaric may become a major cost and you may want to look for alternative solutions.
Also, if your recently crushed fruit chemistry is constantly changing, one option is to blend a sample of berries. This will help create a very homogenous sample and give you a better estimation of what your pH, TA, and Brix are in your juice
16. What is the proper protocol for sampling wine from a tank for plating?
The two most common errors made when sampling for microbial analysis are taking a non-representative sample and contamination of the sample. Taking a representative sample of grape must can be difficult due to the challenge of homogenizing a container of processed grapes. Combining multiple samples from various depths of the tank will help minimize some of the variability that exists within the container. However, you should keep in mind that the microbial populations measured in a tank of grapes might not be as accurate as those measured in a tank of wine that can be mixed to ensure homogeneity prior to sampling. Mixing is particularly important when taking a sample for microbial analysis as microbes may stratify within a tank or barrel. Larger microorganisms such as Brettanomyces tend to settle to the bottom of a tank or barrel while aerobic microorganisms such as Acetobacter will be in higher populations near the surface of the wine where there is a higher concentration of oxygen. Ideally, the tank or barrel will be mixed before sampling. Sampling an hour or two after filling a tank or barrel will also ensure a representative sample. If mixing or stirring a tank or barrel is not an option, then sample from the top, middle, and bottom of the tank or barrel and make a composite sample.
Contamination of samples during the sampling process can lead to false positives or overestimation of the true population. An example of this would be when sampling a barrel, you scrape the barrel thief against the inside of the barrel bunghole. Acetobacter are often in high concentrations around the barrel bunghole as they are aerobic microorganisms. Scraping the wine thief against the bunghole will likely contaminate the wine thief with a high population of Acetobacter that will then be transferred into the wine sample. Results of the analysis will incorrectly indicate that the wine has a high population of Acetobacter when in fact the wine may not. Care should also be taken when sampling from a tank using the sampling valve. If the valve was not been cleaned and sanitized properly, it is likely to contain residual wine. This wine will have a high population of aerobic microorganisms such as Acetobacter and so wine samples taken from the valve will be contaminated. Valves must be cleaned and sanitized before and after use (70% alcohol or SO2/citric solution). In addition, several volumes of wine should also be flushed through the valve before taking a sample.
17. How do you know that your wine is impacted by wildfire smoke?
Smoke taint is becoming a bigger issue as wildfires become more prevalent. The two most common compounds that are known to have a negative sensory impact are guaiacol and 4‐methylguaiacol. These compounds are mostly glycosidically bound in the fruit, so the taste/aromas of smoke taint are not present or at low concentration in the fruit. During winemaking and aging hydrolysis occurs which releases the guaiacol and 4‐methylguaiacol compounds and their concentration increases several-fold. This is usually why winemakers claim that smoke taint often shows up later in the winemaking process which is quite frustrating.
The current tools for winemakers are a bit limited, as guaiacol and 4‐methylguaiacol are volatile aroma compounds that are currently only measured via GC-MS, but there are analytical labs that can measure these compounds and use acid hydrolysis on fruit samples to get an estimated amount of guaiacol and 4‐methylguaiacol. Analytical labs also recommend making a small batch of wine with the fruit in question and send the wine for analysis as well to get an even better idea on the guaiacol and 4‐methylguaiacol levels and if the wines will be impacted by smoke taint. The analysis will cost between $150-200 per sample.
18. Why are pH's high this year in North Coast (CA) Sauvignon blanc- we haven't irrigated as much as normal so the potassium levels are not high.
There are a number of factors that can impact pH. As you point out heavy irrigation has been shown to increase cation uptake (potassium and sodium predominantly). This causes the pH to be buffered higher than it would be without the cations. The same condition can occur with "natural" water uptake. This year much of the North Coast has 100-300 more growing degree days than last year, this paired with better soil water availability than has been scene in years maybe allowing the vines to transpire way more. In so doing pulling cations from the soil. While a complex relationship, wine acidity also plays a role in wine pH. Lower malate or tartrate levels will set the fruit up to increases in pH faster than not. The physiology behind differing berry acid accumulation is worth a post in and off itself but simply put happy active vines early on will increase acid production. It may be worth getting an organic acid profile of your fruit to get an idea if your tartaric acid is on the low end of what you would expect so adjustments maybe implemented next year.
19. What is the difference between Fermaid K and Fermaid O? Can they be used interchangeably?
Because these are propriety commercial products, it is difficult to know that exact compositional differences between the two products. However, the major known difference is that Fermaid K contains diammonium phosphate (DAP) while Fermaid O does not. Because DAP is not allowed to be used during the production of organic wine, Fermaid K cannot be used but Fermaid O can. Fermaid K will provide a greater amount of yeast assimilable nitrogen (YAN) than Fermaid O because it contains DAP.
20. There must be many substitutes to the sulfites added to wine please reveal them?
There are few options that are allowed in winemaking. This is likely first due to the fact that sulfites are naturally produced by yeast, not nearly at the levels found income wines, but all wines "contain sulfites" in the U.S. this needs to be labeled above 10mg/L whether they were added or occur naturally. If you are looking to not add SO2 or minimize your additions you need to address the two jobs sulfites do in wine:
1. Inhibit spoilage microbe growth.
2. Act as an oxygen scavenger.
To inhibit spoilage growth the best options are preventative, there is no easy cheap compound you can add to your wine or must that will do the job of SO2. That is not to say that you cannot make wine without spoilage problems without it. Yeast itself does a great job out competing lots of bad microbes. By creating a high alcohol low oxygen environment very few bad things can grow. Your job as a winemaker then becomes keeping it that way by avoiding any unwanted microbes getting into your wine, as well as keeping O2 ingress very low (for home or very small winemakers this can be difficult). Going into bottle you need to sterile filter, after that if your bottling line and bottles where properly sterilized nothing should be living in your wine. As for oxygen scavenging wine itself has some powerful antioxidants (red, more than white). If you are very careful with your oxygen ingress after fermentation you can preserve many of these antioxidants to scavenge oxygen radicals later in your wine’s life. Addition of tannin products or polyphenol extracts may help increase this capacity, but there are obviously sensory impacts that must be balanced.
One additive option on the horizon in glutathione. In a number of recent studies, it has been shown to inhibits oxidation and even increase the impact of what SO2 exists in your wine already (Fracassetti et al 2013). Unfortunately, I know of no available glutathione product for wine addition in the US currently. A tried and true method that in essentially adds glutathione is to leave a wine on the lees. This causes greater oxidation/reduction capacity and will help to prevent an “oxidized” wine as the reduced amino acids are available to trap what oxygen gets into your wine. The risks associated with this method are that extended lees contact may cause a “reduced” wine as well as impart unwanted flavors from yeast autolysis.
21. We would like to know the pluses and minuses of sequential fermentation.
One of the primary and obvious reasons for simultaneous ML and Alcoholic fermentations is time. Not only are both activities taking place at the same time, but MLF bacteria are not happy in high alcohol environments. Or cool temperatures for that matter. In co-inoculating you are giving the ML bacteria access to the environment that they prefer, as well as access to an early sugar source all but ensuring a quick conversion of malic to lactic acid. If quick acid conversion is your only goal the preferred route is pretty simple. So why do many wineries still fight with sequential fermentations? There has been work that has shown sequential fermentations can increase color stability as well as final tannin content (Abrahamse 2011). There are some conflicting results on how the timing impacts acetic acid production with some suggesting ML metabolism of sugars can increase acetic acid production, while others found no evidence of this pathway being utilized under wine conditions. There is also little evidence for one option being better than the other when comparing aromas, however there are winemakers that have very firm opinions. This maybe based off specific bacteria/timing/yeast strain combinations or some other yet to be uncovered factor. I suspect one of the strongest reasons for the persistence of sequential fermentations is tradition. If someone has had success using a certain method for decades, or generations, it may not be worth the risk to them to try something "new". For at least another century we will have wineries using oak barrels and sequential MLF but hopefully we can move on to using g/L rather than g/100ml as that is a tradition I can't support.
22. We have a lot of dust on our grapes. Does dust have an impact on wine quality? Why are grapes never washed before processing?
No better way to express terroir than to put the earth directly in your wine? I have heard of wineries "washing' their grapes, but it is certainly not the norm. One reason it is not a big concern is because of dilution. Assuming a small cluster of about 100g (3.5 ounces) the amount of dust is likely to be on the order of 0.01g on very dirty fruit. That would mean if the dust was pure flavor it would have to be tasted or smelled at 100mg/l, or relatively close to the sensory threshold of SO2 (depending on pH). For the most part dirt will be inert so our educated guess is in most instances dust would not cause a perceived difference in flavor. That is not to say that it could not impact flavor and some wine regions even use the similarities to the smell of dust in the air to their wine as a marketing point (look up "Rutherford Dust.") Assuming you do not want to evoke the sensation of sitting with a friend enjoying wine next to a vineyard with the subtle sent of a truck having passed over a dirt road in the distance, there are options. One is to spray your vineyards, especially the fruit zone at a high flow rate. Drench the fruit until you have effectively washed off the dust. Second, most of dirt is insoluble, so for a white good clarification should remove your dirt from your must. If it is a red, as very deliberate rack and return will cause solids to settle out of your ferment. Dr. Osborne at Oregon State University has found this to even be an effective way to removal elemental Sulfur.
23. I just purchased a small semi-automatic spectrophotometer for my 500 case boutique Winery. I have what seems like an infinite number of enzymatic test that I can perform. What would you suggest as the most practical initial enzymatic test kits to purchase? And in order of significance which additional tests might I add in the future.
This is entirely dependent on what your needs are and what you can currently do inhouse without enzymatic kits.
- One thing that is hard to do without an enzymatic assay is yeast assimilable nitrogen or YAN. Unfortunately, you need two assays: Free Amino Nitrogen (FAN) and ammonia (NH3). This is an important assay if you have any issues with stuck/sluggish fermentations or microbial growth after fermentation as you may be under/over adding nutrients. If these issues are not a problem for you, then you may not want to test for YAN.
- Malic acid is a nice assay to have as this will help you determine when MLF conversion is complete. This is a great tool to have and is a lot easier than paper/thin layer chromatography. If you do not do MLF at your winery than this test may not be important (unless you want to check if your wine has not gone through MLF)
- Reducing sugars assay is great for wineries looking to ferment to dryness or stopping at a certain residual sugar (RS) percentage. Using AimTab to test RS will give you a rough determination and is more basic and inexpensive. There is also a more accurate (and likely more time consuming) bench top assay called the Gold Coast Titrametic method for reducing sugars.
- Ethanol may be the most important assay as wineries legally need to know the alcohol level for labeling and tax purposes. Using an ebulliometer is an option but it can be time consuming and needs to be recalibrated often. Sending sample for analysis can cost up to $30 a sample, so doing in house can save you a bunch of money.
- Acetic acid (volatile acidity (VA)) Is another useful assay if you have had issues with high VA in the past. There are legal limits to VA, so it is important to test for if there is an issue. If you’re not going to test for acetic acid frequently then it may be easier to send samples to an outside lab for analysis when there is a wine in question. You can also test this by using a cash still and titrating the acid.
- Total and free Sulfite (SO2) can be useful (especially with an automated enzymatic analyzer), but most wineries are already set up for the aeration oxidation or Ripper titration method(s), so they prefer to stick to the bench top method.
24. What DAP or FAN/YAN levels are best for a healthy fermentation? What are the effects of late DAP additions?
The general recommendation is between 150-250 mg/L for a 21-23°Brix must. If you have a higher °Brix must or are using a high nutrient demand yeast strain, then you may want to consider higher YAN levels. These are not hard and fast rules but are YAN levels that have been reported by researchers and yeast manufacturers to result in fermentations with good kinetics. If making a large nutrient addition, make multiple additions of nutrients during the early to mid-fermentation stage rather than one large addition at the start of fermentation. For example, add half the nutrients 12-24 hours after inoculation followed by the remainder of the nutrients around 1/3 sugar depletion. Adding nutrient supplements all at once can lead to a fast fermentation rate, and an imbalance in uptake and usage of nitrogen compounds. Alternatively, nutrient supplements added too late in the fermentation (after 2/3 fermentation) may not be utilized by the yeasts. This is because as the fermentation proceeds ethanol concentrations reach a point that impact the yeast membrane and reduces the ability of yeast to uptake nutrients.
25. Is it better to add distilled, spring water or tap water to your must?
In winemaking you should never be adding large amounts of water in comparison to the total volume (in some regions none is acceptable). However even assuming a very large addition of 20% by volume only very hard water is likely to have dissolved mineral at a level that will have much impact. There is however the chance off aromas being introduced to your wine from any source, so the first question you should ask yourself is if there is anything about the water source you are using that you do not want in your wine. Beyond that distilled/deionized water would be my preference as it will have the most predictable results. Now for brewing or distilling where added water makes up most if not all of the liquid portion of the product distilled water can be problematic, leading to poor mouthfeel and fermentation issues.
26. Our grapes have high elemental sulfur this year due to late vineyard sprays. What can you do during the winemaking process to prevent/eliminate H2S?
The good thing is that it is very hard to get the necessary 10mg/L of elemental sulfur into your wine to make it stinky. This may have been more likely when the products are applied with larger and/or less uniform particles present, but even right after application you have levels that can be mitigated through vinification practices.
- In white wines, settling your wine can reduced elemental sulfur by more than 90% in your clarified must.
- A very deliberate rack and return has also been shown by Dr. James Osborne at Oregon State to effectively reduce residue.
- If you want to further mitigate your risk, reduce H2S production elsewhere through good nutrient management and by using low/no H2S producing yeast strains.
- If you still find you have in your wine, proper use of copper sulfate can help. Just be careful as recent work has demonstrated that excess copper sulfate can form adducts with the H2S that will reemerge in bottle.
- Do not aerate, as that will just cause disulfide formation.