Vacuum Racking

Discussion in 'General Wine Making Forum' started by Bruce67, Oct 19, 2019.

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  1. Oct 19, 2019 #1

    Bruce67

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    Morning from Ohio;

    Have often wondered what effects the vacuum process has on my wines after clarification. It seems that the "boiling" taking place never really stops completely. Does alcohol evaporate during vacuuming and is there a point where you just cry uncle and say enough is enough?

    bruce
     
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  2. Oct 19, 2019 #2

    mainshipfred

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    I hope some of our more scientific members chime in on this one. You're right, it never stops bubbling, boiling, degassing or whatever is going on. I did an experiment once using the AIO and somehow I was able to calculate the temperature required to cause the wine to boil for the Hg of the AIO. The one thing I think I remember is with the wine at 70 or so degrees the Hg of the AIO wasn't enough to make the alcohol start to boil.
     
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  3. Oct 19, 2019 #3

    sour_grapes

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    Yes, water and alcohol will evaporate during vacuuming. BUT, water and alcohol will also evaporate when NOT vacuuming. If you place a glass of wine on your kitchen counter for a few days/weeks, it will dry out, and all the alcohol and water will be gone. It happens faster on dry days than on humid days. It happens faster when you pull a vacuum on it. It happens faster if the wine is warmed.

    One thing to keep in mind that may change your outlook: There is nothing all that special (as far as evaporation is concerned) about the boiling point. If I have a pot of water on the stove at 200F, it will evaporate away, even as it never reaches boiling.

    To directly answer your question, yes, there is a point where your wine is sufficiently degassed, and you should stop. In fact, I think removing all the CO2 is probably deleterious to the taste of your wine. We expect there to be a little CO2 there. IMHO, when I have "overdegassed" my wine, it tasted a little flabby and flat. I no longer do that; I just let time take care of it.

    Another thing to keep in mind is that, during vacuum degassing, the bubbles that you see do not contain all that much gas. If you are pulling, say, 25 inHg, a bubble of a given size has only about 15% as many gas molecules as a bubble of the same size has at atmospheric pressure. But your brain (or at least my brain) says "wow, it is still bubbling a lot, giving off a lot of gas! I better keep going."
     
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  4. Oct 19, 2019 #4

    NorCal

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    I’m with @sour_grapes on this one. Since I’m usually dealing with high pH wines, I need all the residual CO2 I can get. After a year in the barrel, there’s not much, but there is some.
     
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  5. Oct 19, 2019 #5

    sour_grapes

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    I just re-read my earlier post. Although I still "agree with myself," I want to clarify something. I do not think that it is bad to vacuum rack or to vacuum degas. I do the former, and I do a little of the latter. I do not think that significant amounts of water or alcohol are lost during these processes, within a reasonable degassing period. I haven't calculated it, but that is my feeling.
     
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  6. Oct 19, 2019 #6

    Bruce67

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    Thanks for the replies.
    bruce
     
  7. Oct 20, 2019 #7

    mainshipfred

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    I tried to find this out myself with no real luck. Is boiling point and evaporation the same thing? In distilling you heat the liquid to around the boiling point of ethanol which, I guess, causes evaporation of the ethanol but not the water. If you pull a vacuum the boiling point of all the liquids drops. The only simple calculation I could find was:

    The boiling point of ethanol is 79*C and under vacuum (28 inHg) it drops to around 34*C. We typically use a rule of an additional op-temp of 50 degrees Celsius above the boiling point of the solvent is enough to boil the solvent and maintain that boil.

    But I also understand if you leave a glass of wine, water or any liquid out I will evaporate even at temps below the boiling point. So I can only assume boiling point and evaporation are different.
     
  8. Oct 20, 2019 #8

    sour_grapes

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    (For convenience, let's first consider only pure liquids, i.e., not a mixture of different substances.)

    All liquids have a property called its vapor pressure. This is a measure of how strongly the liquid's molecules are bonded to each other. If you had a closed, partially filled container that had only, say, water in it, the "headspace" would be filled with water vapor. The vapor pressure is what the pressure in that headspace would be. Some liquids bond strongly, and so have a low vapor pressure, and others are only loosely bound, and so have a high vapor pressure. As examples, at room temperature, the vapor pressure of ethylene glycol is 0.05 Torr, water is 18 Torr, ethanol is 93 Torr, acetone is 225 Torr. (Torr is a unit of pressure, and is the same as 1 mmHg.) So ethylene glycol binds strongly to itself, (and so evaporates slowly), and acetone is more loosely bound (and so evaporates more quickly).

    Note that the vapor pressure depends on the temperature. In an open container, the boiling point is when the vapor pressure becomes equal to the pressure of the atmosphere above the liquid. At that temperature/pressure combination, the molecules are "indifferent" to whether they are in the gas phase or the liquid phase. For most liquids, there is a well-defined boiling temperature (for a given pressure), and you cannot get the liquid hotter than that temperature. Evaporation, then, happens most rapidly at the boiling temperature. And, as you have noted, the boiling temperature will be lower when the pressure above the liquid is lower.

    When you have a mixture of two liquids, things get more complicated. Now you have to consider 3 different kinds of molecular interaction, say water-water, water-ethanol, and ethanol-ethanol. Now there will not be a well-defined boiling point for them separately, and the vapor that comes off depends on the temperature AND the composition of the mixture. If you have, for example, a mixture that is 95% ethanol and 5% water, the vapor that comes off is 95% ethanol and 5% water (so, as it happens, you cannot use distillation to concentrate ethanol to greater than 95%).
     
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  9. Oct 20, 2019 #9

    mainshipfred

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    Thanks, I think, LOL! When you threw acetone into the picture it started to make sense. Still need to digest the rest of it but I get the concept.
     
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  10. Oct 21, 2019 #10

    Rice_Guy

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    2 cents worth:
    * The solubility of a gas in a liquid is based on Henry’s law.
    Solubility = (Henry’ constant) times (percentage of target gas in the atmosphere)
    ie. The gas in the atmosphere acts as a spring to hold the gas in the liquid. Water, alcohol and CO2 will all have liquid and gas phases and follow Henry’s law. The magic of using a vacuum to degas is that the back pressure of subject gas is reduced so the solubility in the liquid is reduced and we see the effect as boiling.
    The solubility is linear with the pressure and linear with the percent of gas in the atmosphere above the liquid, ie if I have a steam boiler I can contain the atmosphere and keep water in the liquid phase. Alcohol is capable of existing in both gas and liquid phase
    * Alcohol does evaporate to a limited extent, as sour grapes notes, the ratio of alcohol to water evaporated will depend on the back pressure. This is the logic on having oak barrels in a humid/ cool cellar, the atmosphere provides back pressure to slow evaporation.
    * The presence of CO2 in the liquid contributes to the flavor profile. Some companies reprocess wine by adding CO2 to add zing to the flavor.
    In excess CO2 will contribute bitter/ carbonic acid flavor notes, , , so we don’t want to go overboard.
    CO2 creates carbonic acid which decreases the pH and increases the TA.
    The presence of CO2 contributes to a reductive environment which slows oxidation and off flavor production.
    * the magic of vacuum racking is that fresh liquid with dissolved gas is exposed to low back pressure. The depth of liquid contributes back pressure which slows the release of target gas into the atmosphere. ie it still will come out, it just takes longer to reach a new equilibrium.
    * vacuum pumps are rated on how many liters per minute they pull. The cheap $15 ones on the web are rated by are they mainly volume or inches of vacuum, not both. The $100 AC pumps are two stage and do both volume and inches of vacuum.

    There is an argument here on what matters. , , , My opinion is some CO2 is useful in maintaining high quality wine. , , , and if I had no CO2 I would actively add extra inert gas as argon or nitrogen or even CO2.
     
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  11. Oct 21, 2019 #11

    mainshipfred

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    In the last sentence are you referring to the gas in solution or headspace? I have sparging stones and argon and was my understanding sparging the wine removes O2 and CO2. I've been in the habit of sparging my wine prior to bottling to reduce the amount of dissolved O2.
     
  12. Oct 21, 2019 #12

    Rice_Guy

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    In the scheme of things we are consuming the wine (alcohol) so that is what matters. That noted, what we have access to is the head space above and void volume when we start filling a carboy or bottle.
    The commercial systems I am aware of do tricks as add a drop of liquid nitrogen before adding wine or pulling a vacuum on the bottle before bottling or putting a slight positive nitrogen pressure on a floating lid. They are preventative in action, not attempting to remove oxygen. manshipfred, a guess on my part is that you haven’t decreased the atmospheric pressure or the percentage of oxygen so you have no measurable effect by sparging argon, , , and the carboy has significant mass so what effect occurs is awfully slow.
    Pushing the pencil, To saturate a 750 ml bottle with O2 takes 4.5 to 5 ml of pure oxygen. At 20% of the atmosphere we breathe, this is 22 to 26 ml of air, a cork plus 3/4 inch of ullage is about 25 ml therefore a cork pushes enough air onto the bottle to saturate the contents. (smaller containers show a higher percentage saturation) , , The effect is additive, ie air in carboy, racking, primary all contribute to oxidative effect. If you are primarily doing reds you have a good slug of antioxidants and can get away with adding oxygen occasionally. If you are doing whites and fruits every place to reduce oxidation will help the quality.
     
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  13. Oct 21, 2019 #13

    sour_grapes

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    Quoting myself to issue a clarification on an earlier post:

    That 95% ethanol/5% water example is not a generic result. That particular mixture is called the azeotropic mixture. For other compositions, the vapor that comes off will not have the same composition as the liquid. For example, if you have 85% water and 15% ethanol, the vapor that comes off will be much richer in ethanol than in water compared to the liquid. I cannot say a lot more on this subject before running afoul of the, errrrr, prohibition on discussing a certain topic on this forum. :D
     
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  14. Oct 21, 2019 #14

    mainshipfred

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    In the context of the thread I really don't think you are close to running afoul. But then I'm not a moderator.
     
  15. Oct 21, 2019 #15

    mainshipfred

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    I actually have the Vinmetrica DO analyzer. I try to keep everything between 10 and 15% O2 saturation or close to it. Perhaps I should keep whites on the lower end of the scale.
     
  16. Oct 22, 2019 #16

    Rice_Guy

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    * I have used the vinmetrica 100 and 300 so I am guessing what the DO number means and test method does. Therefore if a liter (1000ml) is saturated with 6 to 7 ml of pure oxygen you are running at something between 0.6ml and 1.05ml of oxygen dissolved per liter, ie there is enough oxygen there to react with molecules that have a low redox potential. My guess is the learning with a vinmetrica DO is what risk we put the wine to, ie higher percent means more risk. Curious to hear more as number before racking and after, , again am guessing based on Hatch lab DO probe.
    * at winemaker conference it sounded as if UC Davis was using a probe which measured redox potential to follow degradation of molecular soup (at a couple $K per probe). A SO2 reading should reflect the redox potential and if I was looking for more detail the rate of change in SO2 should reflect the overall redox potential.
    * oxygen is the enemy, we are talking shelf life which is not hard and fast, , I may recognize acetaldehyde at 50 ppm but someone who hasn’t had training may say “off” or “interesting/ pleasing flavor but it wouldn’t score at a contest”.
     
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  17. Oct 22, 2019 #17

    mainshipfred

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    I only test the DO prior to bottling not between rackings.
     
  18. Oct 22, 2019 #18

    RonObvious

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    Just an observation - I use the AIO vacuum rig for bottling. Which works great. The only slight downside to vacuum bottling is that my basement winery gets foggy within minutes. Not kidding! When I'm bottling, you can see a foggy haze in air inside the winery. I feel like if I do more than a few dozen bottles at a time it might start to rain in there! ;)
     
  19. Oct 22, 2019 #19

    stickman

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    Technology continues to drive professional winemaking towards understanding more of the details. Understanding how oxygen affects wine has always been studied and many concepts understood, but with all of the variables involved, applying the concepts and achieving consistent results has traditionally been difficult. A new test for wine and must measures the rate oxygen is consumed over time, the value obtained is expressed as mg/l/day and indicates how sensitive the wine is to oxygen as well as an indication of aging potential. The ranges are fairly wide even for the same type of wine, which explains for example that not all wine is age worthy, something we already knew, but now a number can be assigned. With wine the test is conducted over a period of several days, for must the test is completed in 15 minutes, below is an example of the type of data obtained.

    Oxy.png

    Oxy2.png Oxy3.png
     
  20. Oct 23, 2019 #20

    vacuumpumpman

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    Are you using the allinonewinepump ? It should not get foggy as it is oil less vacuum pump
     

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