I recently opened a 2015 Russian River Chardonnay that had thrown a significant amount of acid crystal deposit. No biggy, just means I should look forward to a high acid wine right? To my surprise the wine was rich, round and very ripe, it lacked energy and brightness. As far as I know the wine was never frozen, the cork was in good shape, not at all pushed and the wine otherwise was in fine shape. So how does a wine that seems relatively low in acid, deposit a lot of acid crystal in the bottom of the bottle?
harmless tartrates that precipitate out in cold. Tartaric acid. The loss of this acid, to my palate, doesn’t change overall wine acidity perception.
Yep yep yep.
I get that, but to my understanding of the chemistry involved is that acid in the liquid needs to reach a level of supersaturation for the cold to form crystals in the first place.
The crystals are what’s called cream of tartar in the grocery store baking isle. They’re a combination of tartaric acid and potassium and partly depend on whether and how the wine was cold-stabilized. Some wineries chill the wines at very low temps, like below freezing, to ensure that they don’t get the precipitation later, whereas others stabilize at slightly warmer temps above freezing because they feel that the extreme cold can strip out some flavors and aromas as well. I don’t know - I’ve had wine that was cold-stabilized in a garage that was substantially below freezing and that wine was pretty good.
But if they do the cold stabilization at a higher temp, if the wine gets colder, it may throw some additional crystals.
In any event, you have a metal and an acid - it’s a salt. Minerals man! Your wine has minerality!
Mike - In simplest terms my guess is that your wine has a higher pH(3.0-3.5) and some residual sugar that cuts some of the acidity you might taste. The solubility of tartaric acid is a function of pH, concentration, and pairing ions. It’s not the only acid found in wine.
To cut to the chase, the fact that they are there and the quantity of them has no direct correlation with how acidic a wine is - period.
Greg’s explanation is awesome - the only thing to add is that it’s now possible to do tartrate stabilization via an ion exchange system that takes a mere few hours instead of chilling tanks for 10 days or more . . . And there are now ‘chemical adds’ that winemakers are beginning to use to accomplish the same results, some of which should be on the market from Europe by now.
The fact that a wine throws tartrates or not also has no implication in terms of taste or quality - many smaller wineries these days simply do not go through the process to cold stabilize because they feel that their customers will not ‘be alarmed’ if they see these crystals, which can look like cut glass sometimes, but larger producers are apt to always stabilize these tartrates so they do not fall out of solution.
pH 3 sounds very low to me, as very few wines outside sparkling wines go under 3. pH 3,5 isn’t particularly low for a white wine, but quite normal to low-ish to a red wine.
And tartaric acid dropping out of solution also means a drop in acidity (after all, there’s now less acid in the solution). However, this drop is normally quite minute and seldom particularly perceptible, so there’s no worry that the wine would feel noticeably lower in acidity if wine crystals form.
Gary, Greg & Larry
Thank you for answering my question, I was under the impression the crystals were just acid not a salt, so I learned something. I think Gary is really on to something with the residual sugar as the wine was all over ripe fruit and charred wood. This wine was from a very small producer so I think Larry hit it on the head there. And Greg there was very little overt minerality to the wine a little wet cement on the nose but that was really it.
This is a topic I’m not entirely clear on. What gives the sensation of “acidity”? Is it the proton (H+), or is it the base (tartrate in this case). pH is a measure of the concentration of H+ ions. The crystals are Potassium Tartrate, meaning that the proton is left behind in solution. So tartrate precipitating out doesn’t change the pH (much, except it gets a little more complicated). This abstract suggests that it’s mainly the proton concentration that gives the sour sensation of acidity:
It’s been… too long, since I took college chemistry.
Once the Potassium Tartrate precipitates out (say in a cold stabilization), and then wine comes back to regular temperature. Does the equilibrium actually drive more tartaric acid to dissociate to ionic states, thus make the wine more acidic than before (Le Chatelier’s Principle)?
I believe it’s a buffered solution so pH will not change much, even though the tartrates precipitate out.
Guys, the answer is 3. Duh.
If the wine maker tries to bump up acidity by adding tartaric acid, it could precipitate wine diamonds.
The exact cause of the perception of acidity isn’t yet agreed on by scientists that study this. The perception is due mainly/entirely to the TA (total acidity) of the wine, but why isn’t well agreed on. pH is due to the number of Hydrogen Ions (H+) in solution…and H+ seems like would be the cause of tartness…so tartness should be based on pH, not TA. Tartaric is a weak acid, meaning that not all H+s will dissociate/detach from the tartaric molecule when it’s in solution (strong acids dissociate all H+'s). The most common theory (on why TA determines acid perception) is that when a tartaric molecule enters a taste bud (taste buds look like tiny caverns that molecules can go in & out of) the tartaric molecule can dissociate its H+s while inside, and then reassociate when leaving (depending on the pH).
Anyways, a wine will be noticably less tart after crystals form. The wine will still be fine tho.
Tartrate crystals (TC) can only form when the wine is supersaturated with Potassium Bitartrate (PBT). Even then, they might not form for a variety of reasons: manoproteins (a part of Lees) can prevent this, same with Gum arabic (a wine addition, also causes the wine to appear more sweet).
When the crystals form, two things happen: 1 the TA (total acidity) goes down, indicating that there are fewer acid molecules in solution (repeating what several folks mentioned above).
2 If the pH of the wine is below ~3.95 when the crystals form, then the pH goes down (higher acidity), strange as it might seem (the lower the pH, the larger the drop). If the pH is higher than ~3.95 (when the crystals form) then the pH will go up (lower acidity). Note: 3.65pH is widely quoted (as the isoelectric point), which is true for a water solution…adding alcohol raises the isoelectric point, typically to 3.95pH or so.
Most wine is lower the 3.95pH, so it odd and interesting that crystals forming can cause the acidity to both go up and down at the same time. Just shows how weird and complicated acidity is. Anyways, this is the equilibrium you were asking about Carter.
Someone (the Aussies I think) did research and discovered that cold stabilizing a white wine reduced the amount of colloids in solution (permanently suspended solids, mostly lees), and that negatively affected the wine’s texture and aromatics…so while most supermarket chards/etc are cold stabilized, many/most ‘higher end’ whites aren’t for this reason.
Note that cold stabilizing a wine involves cold temps + time…usually more than a week, esp at fridge temps. So if you limit the amount of time your whites stay in the fridge, and keep them in the 50’s or so the rest of the time you shouldn’t have problems with crystals forming.
Perception of sour seems a bit complicated, but appears to measure both protons and protonated acids.
I assume it has to be, right? Acetic doesn’t taste the same as phosphoric acid, or malic, citric, etc. The base (and/or it’s protonated form) has to contribute, no doubt.
There is evidence they are perceived as equally sour at the same molar concentration, but I don’t believe it has been conclusively demonstrated.
The different overall taste is probably related to other things, either because most substances trigger various receptors or because of other impurities.
As Eric mentioned, there is still a lot that is not understood about taste.