Category: Winemaking Fundamentals

Hi Clark,

What’s a good rule of thumb for O2 levels before filling tankers?

Matt

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Hi Matt,

Short answer is, you’ll do well to get below 1 ppm, and 4 ppm is where most wineries panic and sparge w N2 upon receipt.  I hate this procedure, which strips volatiles, so let’s avoid pickup in the first place.

Let’s first talk about how you achieve this, then some debunking with theory.

 

Tips for loading a wine while minimizing DO pickup:

1. Always ship full compartments if you can.  If multiple compartments, top the biggest one and go partial on the other smaller volume.
2. Lay down a layer of inert gas approximately 1 foot high.  Calculate the number of standard cubic feet this will take by measuring the length and width of the compartment at its widest, for example 20’ long X 8’ wide x 1’ deep = 160 SCF.  The best way to lay down a layer is with pelletized dry ice.  This disperses in a small amount of wine, so it doesn’t boost your dissolved CO₂ very much, and is still a good practice for reds.  One pound of dry ice converts to 30 SCF, so in this example, throw in 5-6 pounds. Next best is to deliver this gas in a laminar fashion through the sending line.
3. Always inert the lines. Any gas will do, but the heavier than air  (CO₂, Ar) are better blanketers. Go right through your centrifugal pump.  Any flow up to 1000 SCFH will lay laminar into the truck, creating a blanket because the gas is cold.  This layer will persist long enough for the pumping to occur.
4. The best loading pumps are magnetic-driven closed housing centrifugals.  Your standard winery centrifugal has a spring-compressed carbon seal which sucks in air, especially if the seal has been scored by particulates.  If you have one of these, keep your seals ground smooth and replace your springs every year or two.
5. If you have a partial tank, your blanket will disperse in transit, so you have to gas the headspace.  Laminar argon is best for this because it’s faster to deliver 1.25 volumes of argon than 4 volumes of N₂ (see Argon, What A Gas).  CO₂ may be used if you don’t mind the pickup.
6. Measure, measure, measure.  Measure the wine in the tank at start and in the truck at finish.  Measure the top of the headspace as you evacuate with laminar flow.  Measure the DO upon arrival.

 

What is missing from all this standard dogma?  The simple question: “Why do you care?”  Big young reds will gobble up 4 ppm in a few hours, and often benefit from the experience.  A delicate Sauvignon Blanc, however, may be completely transformed by that amount of pickup.  Know your wines’ Oxygen Appetites, which vary 10,000-fold.  Yes, that’s a plug.  But as you well know, oxygen is not always the enemy.

Clark,

The same red wine shows the following chemistry in adjacent years:

’11 pH: 3.65 TA: 6.2 g/l
’12 pH: 3.45 TA: 5.9 g/l

How does the Total Acidity level AND the pH rise at the same time (since higher pH indicates less acidity)?

Ron

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Dear Ron,

An acid is any dissolved substance that can release a proton.  Since the element hydrogen is just one proton with one electron in orbit around it, we also call this a hydrogen ion (H+).

The acids in wine are weak acids, which means they can dissociate a proton (HA –> H+ + A-) but can also take it back (HA <– H+ + A-).  We write these together as an equilibrium (HA <=> H+ + A-).

In juice, the two acids involved are tartaric, which is stronger, and malic, which is weaker.  This means that at any given pH, the tartaric acid will be more dissociated than the malic.  Both of these acids contain two acidic protons, so we write H₂Ta and H₂MA.

The titratable acidity (TA) measures how many dissociable protons there are without regard to whether they are actually dissociated or not at the moment.  In other words, the H’s on both sides of the equilibrium.  This is like the cops on the payroll.

We care about TA because it tells us how the wine tastes.  That’s because when we put wine in our mouth, our glands keep secreting basic saliva until the wine is neutralized completely.  That’s called a titration.  We get the sensation of sourness or tartness, and also the palate-cleansingness of all that saliva.

The pH measures only the free H+.  You can’t taste pH (only its effects, and only if you are very, very good).  But the free protons are the cops on the beat, out there fighting crime.  The pH determines all the chemistry and microbiology of the wine: how fast it ages, how prone to spoilage, how reactive with oxygen, how effective SO₂ is – everything.  The sourness of TA has nothing to do with any of this.

pH is regrettably upside down. Higher free H+ means lower pH, because it’s really the negative exponent.  pH 3.0 means the ratio of water molecules to free H+ is 10^-3, or one in a thousand, whole pH 4.0 means 10^-4, or one in a ten thousand.

The A- parts left over when the H+ departs are called conjugate bases.  In juice, these will be tartrate (Ta^2–), bitartrate (HTa-), malate (Ma^2–) and bimalate (HMa-).  These can hook up with other positively charged elements besides hydrogen ions (H+), principally potassium (K+).

The wine’s resistance to pH change is its buffer capacity, which has to do with how much of these potassium salts are around, providing conjugate bases over and above what is paired with the available H+.  The effect of these is to pull protons away from the free pool we measure as pH.  If there’s a lot of buffer capacity, we will have a high concentration of K+ and a high pH even if our TA is also high.

The other thing that matters is the ratio of tartaric to malic.  A pure tartaric acid solution has a much lower pH (higher free H+) than a pure malic acid solution, thus the higher the tartrate component, the lower the pH.  When the pH and TA are both high and the potassium is low, the cause is high malic acid.

This happens in certain varieties like French Colombard, Petit Verdot and Norton.  It can also happen because of drought. Low soil moisture in winter causes early budbreak and grapes maturing too early in the season, when there is not enough time for the malic acid to be metabolized.

Hot weather can shrivel the grapes, causing the acid to be more concentrated and the TA to rise.  This has happened the last two years in California.

Think of the cops analogy.  If you have lots of cops on the payroll (high TA) but few on the street fighting crime (high pH), where are the cops?  They’re in the donut shops!  So either you have a whole lot of donut shops (high K+) or just a few very good Krispy Kreme donut shops full of cops (high malate).

More about pH and TA in my blog about acid adjustment.

If you have a real Jones for this kind of stuff, and for anyone wishing to enter winemaking, let me shamelessly plug my Fundamentals of Modern Wine Chemistry course, which tackles this as a foundation and goes on to address much of the stuff you really need to know from an Enology degree from Davis or Fresno.  There’s also a 500 page syllabus loaded with articles on a wide variety of practical winemaking topics, with the entire first 50 pages dedicated to pH and TA.

Hi Clark,

I have been working a blog post to the PA wine industry regarding how winemakers can deal with high potassium wines.  For the past few years, we’ve been dealing with wines that have an extremely high pH (4.0+) and usually the TA is low, too (<6.0 g/L).

Now, I’ve tried to make tartaric acid additions to these wines, but often, the TA will go up and the pH will hardly move.  Of course, then I am dealing with a high pH, high TA situation.  Ironically (or perhaps, no so), we have been getting more phone calls regarding high potassium levels in the vineyard or in harvested fruit, so I’m currently guessing many are dealing with high potassium situations.  I recalled that the use of ion exchange or ED may be applicable for high potassium wines to reduce the potassium concentrations and potentially alter the pH to a more reasonable level in the wine.  I’m contacting you to 1) see if this is the case, 2) if there are any great resources that you can recommend for winemakers to alter this problem in the cellar, and 3) if there are any companies on the eastern part of the U.S. that can offer these services (ion exchange, ED) to winemakers in the region?

Any help that you can provide will be GREATLY appreciated.  I’ve already referenced your book and few online articles that I have found regarding the situation.  Otherwise, I hope this harvest is treating you well.  Best, Denise Gardner, Penn State Enologist

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Hi Denise,

How very fine to hear from you.  I am quite impressed with the program you’ve put together and read your weekly blog updates with relish.

Your question involves a basic tricky problem which confronts winemakers all the time.  They often report adding tartaric acid to no effect.  This is an illusion.  No need for IX or ED technology – the solution is easy once you understand what’s going on.  This is the first thig I deal with in Fundamentals of Modern Wine Chemistry and it takes a while to explain.  Let me try.

Tartaric acid has the following dissociation equilibria:

H₂Ta  <=>  H+  +  HTa-  <=>  2H+  +  Ta^2– , with pKas of 3.0 and 4.2.  The bitartrate curve (HTa-) peaks at pH 3.6 and is rather low at pH 4.0.

Let’s break these down into the two separate equilibria:

Eq1:    H₂Ta  <=>  H+  +  HTa-               pKa = 3.0

Eq2:    H+  +  HTa-  <=>  2H+  +  Ta^2–   pKa = 4.2

In the normal case, K+ has been exchanged for H+ so you have a lot of bitartrate buffer but K+ is the counter ion.  This combination should precipitate as KHTa, but it doesn’t because the pH is so high that much of it is in the TA^2– form.

Now think about what happens when you add a little more tartaric acid (H₂Ta).  Say you add 1.0 gm/L.  Initially, the pH will shift down, but you have a lot of buffer present, so maybe you get to 3.85.  Now you have a even more tartrate present and a higher percentage in the bitartrate form, plus lots of K+, so you get a precipitation.

Since you’re lowering the TA by removing a titratable proton (in KHTa), the TA comes back down.  At the same time, you are removing material from the left side of Eq2.   Mass action will make this equilibrium shift to the left to compensate like any buffer.

Notice that this decreases the free H+ from 2 to 1.  A decrease in H+ is the same as an increase in pH. Net effect is that your TA goes down and your pH goes up.  It’s entirely possible to end up back where you started.

Now Eq1 mass action would make your pH go DOWN, but it only operates strongly at low pH.  In sum, when you cold stabilize (precipitate KHTa) above 3.6, your pH goes up.  If you start below 3.6, your pH goes down.  Magic.

So basically, your problem is that you aren’t adding enough tartaric.  Because you chickened out and added less tartaric than you need, you think nothing happened. But that’s not true, because you have removed a lot of potassium.  You just need to keep going.

Generally speaking, the right addition is to 3.6.  At this pH, you get the maximum KHTa precipitation and no pH shift.

Note:  If the TA is higher, sometimes the cause is high malate rather than high K+.  In that case, double salt (aided by crossflow clarification) or a malic-loving yeast is the solution pre-fermentation, or ED afterwards.  But always test first by correcting a sample to pH 3.6 with tartaric and doing an overnight freeze/thaw.

Let me know if this needs further clarification.