Cold Stabilisation - Step by Step

[medpretzel]

I'm first going to post this thread in this section, although it will eventually be moved over to the tutorial section. I just thought I'd start posting it "live" instead of all at once. That way, if anyone has questions along the way, they can ask, and can be addressed in the tutorial as well.

As some of you know, I have started some grape wines from juice I received from a local winery this autumn. There were some "acidity" issues, and with one, I did a MLF. The others, I chose to rely solely on cold stabilisation, which will be presented in the following posts.

I also make some fruit/flower wines, and I will be comparing the effectiveness of cold-stabilisation to that of grape wines.

I would like to encourage questions, comments, critique, and anything else you can think of. If I haven't addressed something, please let me know.

So with no further ado, let's get started.

[medpretzel]

Theory:

Unfortunately, there is not a lot written about cold stabilisation. We know it works, but how it exactly works is still somewhat of a mystery (to me, at least). What I have found is this:

From Progressive Winemaking (Duncan, Acton)

Tartaric acid is usually the major acid found in grape wines produced from fully ripe fruit. In small amounts (1-2 p.p.t.), it improves the keeping qualities of a wine, but if too much is present a hard sharp acid flavour will obtrude on the palate. The monopotassium salt of tartaric acid, better known as cream of tartar, is less soluble in wines than in the unfermented must. Maturing wines containing cream of tartar thus tend to deposit this salt during storage and gradually build up a hard crystalline layer of tartrate on the walls and base of the container. This deposit consitutes the so-called wine stone or argols mentioned in many books on winemaking. Since this process occurs slowly over a long period of time, persistent hazes consisting of tiny crystals of cream of tartar in suspension may be observed in the wine until the excess tartrate has all been precipitated. Refrigeration considerably hastens the rate at which cream of tartar is depositied and is often practised commercially to stabilise the wine in this respect. The wine is simply chilled to a temperature just above its freezing point and held under these conditions for a few days until what is termed tartrate stability is achieved. It is then racked off the depost of cream of tartar while still cold to prevent the crystals from redissolving. Small amounts of tartaric acid are unlikely to provoke this problem, however, and even if it does arise the excess cream of tartar can always be removed by refrigeration. This risk is worth taking anyway in view of the benefits the presence of a little tartaric acid convers on a wine.

My friend CJJ Berry wrote this on tartaric acid (First Steps in Winemaking):

Tartaric Acid
Is that found in the grape (or raisins, sultanas and currants) and is said to improve the vinous character of the wine, but is often unstable, being thrown out of solution in the wine as tartrate crystals. Incidentally, although tartaric is the principal acid in grapes, there is usually a high proportion of malic also.
The acid sare not confined to these fruits and are often found alongside one another in varying quantities, a little citric where malic predominates, and vice versa, for instance.

A general site for some introductory theory:
From: http://www.wineintro.com

The purpose behind cold stabilization is to remove all tartrate crystals from a wine during its fermentation stage. Tartrate Crystals are also called "wine diamonds". They are a natural product of the wine, and form when the wine gets too cold. It is in essence cream of tartar, forming because of the temperature change. Think of sugar turning into rock candy and you'll have a good mental image.

Tartaric acid is a normal grape acid. Potassium also exists in grapes, and when these two things bind together under chilly conditions, they form little potassium bitartrate crystals, which then settle to the bottom of the bottle. They're completely harmless, and quite natural. The problem, of course, is with appearances.

While in Europe these crystals are accepted as a sign that the wine is a natural one, and even appreciated, Americans are used to wine being clear, pure, filtered, processed and de-sedimented. Consumers often panic when they see little crystals in their Chardonnay, thinking they are impurities or even bits of broken glass. They often refuse to drink the wine and return it to the winemaker (who promptly serves it to his own family). Cold Stabilization is a way to prevent these returns from happening.

How is Cold Stabilization Done?

Since the tartaric acid and potassium are natural components of grapes, they cannot really be removed. To make sure crystals don't form in the consumer's home, therefore, the winemaker forces all crystals to form at the winery.

Usually the main stainless steel fermentation vessel for the wine has a cooling system on it. After the fermentation is complete, that vessel is plunged to near-freezing for 3 to 4 days to force the crystals to form. The crystals stick to the sides of the vessel, and when the wine is then removed, the crystals remain behind. Some winemakers argue that a portion of the flavor and uniqueness of the wine remains behind as well.

Cold Stabilization is normally only done to white and blush wines. This isn't because red wines do not form crystals - any wine will form crystals, since every wine is made from grapes containing the ingredients for crystals. However, since crystals only form when a wine gets very cold, red wines rarely show crystals, since red wines are served at a relatively warm temperature. They should never reach that cooler, crystal-forming temperature.

This being given, I have a plan, but a new list of questions.
1. What is the freezing point of wine?
2. I need to calculate at least "a few" days of cold weather.
3. This will be more efficient on grape wines than on other fruits.
4. I will need to act quickly once the crystals have formed, and when I feel it is done precipitating.
5. How long will I have to wait? What is considered a few days? 3? 6?
6. Where will I put the demijohns?

These are the general comments and questions I will be researching before I start.

1. What is the freezing point of wine?
From http://www.wineintro.com/basics/freezing.html

Wine is mostly water, but the alcohol in it lowers the freezing point. So depending on how much or how little alcohol percentage is in the wine bottle, your freezing point of the wine is probably around 15F.

2. I need to calculate at least "a few" days of cold weather.
I checked various places for local weather. The attached image is my forecast. Not ideal, but we will see if it's good enough to cold stabilise.

4. I will need to act quickly once the crystals have formed, and when I feel it is done precipitating.
I've made sure I have enough demijohns to be able to rack efficiently when I'm outside.

5. How long will I have to wait? What is considered a few days? 3? 6?
Okay, I'm going to take an average and say 5 days. This means, by the 7th of December, I will rack the existing wines into new demijohns.

6. Where will I put the demijohns?
I have opted for the veranda. It is somewhat warmer in there, but they are protected from animals and the elements. I have a digital thermometer to give me both celcius and fahrenheit readings.

[medpretzel]

These answers weren't enough for me, so I did some more research:

http://vintessential.com/pdf/COLD%20STABILITY%20OF%20WINES%202003%20Oct.pdf

Optimising refrigeration usage for cold stabilisation of wines
Greg Howell and Marco Vallesi
Vintessential Laboratories

Introduction

The prevention of tartrate crystals in bottled wine is an important task for the winemaker. Although the crystals are harmless, the average consumer isn’t likely to see it that way. With all the talk of contamination of foodstuffs, it is deemed necessary to ensure that wine is cold stable, i.e. that no tartrate crystals are present in the finished product.Cold stabilisation of wines takes a considerable amount of refrigeration power, and can cost a considerable amount of money. Winemakers should always strive to use the minimum amount of refrigeration to make the wine cold stable. Not enough refrigeration and the wine won't be stable, although too much refrigeration will certainly make the wine stable but will waste refrigeration resources unnecessarily.

Several techniques are in use to check the cold stability (also known as tartrate stability) of a wine. The most commonly used techniques will bediscussed in this article.

Chemistry
The chemistry of tartrate stability is quite simple in theory, but a number of factors exist that make it a bit more complex in practice. The crystals in question that are formed in wine are potassium hydrogentartrate (KHT), also known as potassium bitartrate. The crystals form when the wine is no longer able to keep them dissolved. Both potassium ions and tartaric acid are present in the grape at picking and so in the juice at crushing/pressing. However during winemaking changes occur, the major one being that alcohol is formed. Many ions such as hydrogen tartrate are less soluble in a water/ethanol mixture than in pure water itself and so can precipitate out as the composition of the wine changes.Other changes such as pH, addition of more acid species, temperature changes and the presence of high moleculare weight materials such asproteins and polyphenolics, also affect the solubility of KHT. Calcium tartrate crystals can also be formed in wine. This is much less common and will not be discussed in this article. Suffice to say that formationof calcium tartrate is time dependent and can take months to develop.Therefore calcium-based additives should be avoided.

Tests
Several different techniques are in use to check the cold stability of any particular wine. They range from simple non-laboratory checks to lab tests that require more sophisticated equipment. None of the tests are difficult toperform if carried out with some care. However, it is important to note that not all the tests discussed are recommended as reliable indicators of coldstability. They are simply discussed as they all still appear to be used in the Australian wine industry, sometimes with disastrous consequences, as we willsee. Each one of the tests will be discussed below:

1. Conductivity Change
This test requires the most equipment of all tests discussed and therefore is the most costly to set. The major pieces needed are a refrigerated waterbathand a conductivity meter with a temperature probe. The test requires a winesample to be cooled to 0oC and its conductivity measured. Finely ground, pure KHT is then added to the sample and the conductivity measured againuntil a constant reading is produced. A change in conductivity over a set limit is regarded as unstable. A limit of between 3% and 5% is quoted as being generally accepted, however variation of this criteria between wineries is also noted. An extensive study of cold stability methods by Leske et al found several problems with this technique and stated; “the (conductivity) method is inappropriate for the prediction of cold stability”. We have not used this technique in our own lab, but we have some clients who do. One client who previously used the conductivity method, stopped doing so after a container of their wine had to be recalled from English supermarket shelves after a tartrate deposit formed. A very expensive lesson indeed! Although we had performed the testing needed for Export Certificatesfor this winery, cold stability testing is not generally needed for these Certificates. Needless to say, we do not recommend the conductivity method.

2. Concentration Product
This method uses the concentration of potassium, tartaric acid, alcohol and pH to compute a number that is then compared to published limits for differentwine styles. Table 1 below shows a typical set of limits
Wine type CP values x 10-5
Dry white 9.4
Rose 8.8
Dry red 17.6
Sweet white 6.8
Port 10.6
Sherry 5.7

Obviously one major drawback of this technique is to do all the measurements first assuming the winery lab has the relevant equipment. This would only beso for a very small number of large winery labs. A further complication is thatthere is a range of published limits and that disagreement appears to exist asto which is the better set of limits to use. Due to these constraints, this technique does not appear to be very popular in the industry.

3. Freeze/thaw This test is relatively simple and requires no special equipment. A sample of filtered wine is placed in a commercial freezer for a set period of time (usually at least overnight), and then allowed to thaw out to ambient temperature. Any crystals observed after thawing indicate that the wine is not cold stable. In the Leske study, it was observed that this test tends to be more severe thanothers and so could lead to longer treatment times for the wine than is necessary, thereby using more refrigeration power than optimal. Other authors have also observed this. It was also pointed out that conditions of this test are not standardised and so some variation of results would be expected. In fact, different freezer compartment temperatures were measured and found to vary from –10 to –27oC.

4. Storage at –4oC for 72 hours
This test is the one that appears to be the most commonly used. We use this method in our lab and the only major piece of equipment required is a small waterbath that is capable of holding a temperature of – 4oC. Samples are filtered, held at -4oC for 72 hours and then inspected under bright light for any crystal formation. The samples are further examined afterwarming to ambient temperature, and if crystals are still present then the wineis deemed unstable.

As stated above this is quite an easy test to perform. It is important to ensure the bath temperature is accurately measured and that the wine is well filtered into clean containers. Obviously one drawback of this method is that it takes 3 days to perform.The Leske study showed that the wines checked by this method compared best with long term storage stability of wines.

Conclusion
In order to achieve cold stable wine with the optimum use of refrigeration, asample of the stabilised wine should be tested. Four different test methods have been reviewed. It is recommended that the “Storage at –4oC for 72 hours” test be used as the best guide for cold stable wine.

References

1. Iland, P; Ewart, A; Sitters, J; Markides, A; Bruer, N.G.C; “Techniques for Chemical Analysis and Quality Monitoring During Winemaking”, 2000,

2. Leske, P.A; Bruer, N.G.C; Coulter, A.D; “Potassium tartrate – how stable is stable?” Proceedings of 9thAustralian Wine Industry Technical Conference, Adelaide, South Australia, 1995, 39-45

3. Rankine, B.C; Pocock, K.F; “Wine stability tests for quality control”, Aust.Wine Brew. Spirit Rev; 96, 12, 1976, 24-254. Baldwin, G.E; “Tartrate instability; chemistry, testing and physical methods of removal”, Proceedings of ASVO Seminar, Reynella, SA, 1986, 5-14

Okay, some more questions have been answered. "A few days" means 3 days. The temp needs to be -4 degrees C. Using the WAH calculator page (http://www.winesathome.co.uk/downloads/calculator.htm), -4 degrees C equals roughly 25 degrees Fahrenheit (for those of you not on metric). Well, although not optimal and stable at -4 in my area, I will go ahead and try this anyway. 4 of the 5 nights will get down to at least -4....

[medpretzel]

Things to prepare for:
1. Airlocks - I have chosen pure vodka for the airlocks. Although I don't anticipate hugely freezing temperatures, I would like to err on the side of caution.
2. Make sure you have sanitised, empty demijohns ready for racking. This might be a problem for me, but I will "rack and wash" as I go along.
3. The cold! Remember that if you bring your demijohns inside to rack at the end, your demijohns will have condensation on the outside of them. This makes them slippery and you need to have either a carrying strap or gloves with slip-proof rubber on them.
4. Protect them from light. If you are concerned about the color, make sure you cover them up.
5. Protect the wine from the elements and wild animals. Preferably, a closed-in area is optimal. If you don't have that, I would suggest a tarp or some other waterproof/snowproof covering. Make sure those bears, wolves and tigers can't get to it either.
6. Keep good notes (that should be a given).
7. Keep your wines labeled in such a way that you can't lose track of them. I used to use taped-on labels on my demijohns until I realised that they fall off with the condensation and the cold.

[medpretzel]

Day 1.
Temp: 10.1 degrees Celcius (ca. 50 deg. Fahrenheit)

[medpretzel]

Some notes because I'm doing this to lose a bit of the acidity in the wines.

http://www.fst.vt.edu/extension/enology/EN/37.html

Bitartrate Stabilization and Changes in Titratable Acidity and pH

Wines with initial pH values below 3.65 show reductions in pH and titratable acidity (TA) during cold stabilization, because of the generation of one free proton per molecule of KHT precipitated. The pH may drop by as much as 0.2 pH units, with a corresponding decrease in TA of up to 2 g/L. By comparison, KHT precipitation in wines with pH values above 3.65 results in higher pH levels, and corresponding decreases in TA. This is the result of removal of one proton per tartrate anion precipitated. The above values represent ranges seen in practice and may vary.

[Hippie]

Danina, is your aim to help the wines clear or to precipitate tartaric acid, or both?

[medpretzel]

both.

[medpretzel]

Day 2....
Wines look unchanged.
Temperature at 2.7*C...

UPDATE: I took new pH readings after calibration of my pH meter

Red: 3.95
Rose: 3.55
Chard: 3.22

[medpretzel]

Day 3:
Temperature at 9:30 this morning: -4.5*C...

Chardonnay has developed some crystals!!! The others haven't. I took a pH reading yesterday afternoon, and will post them later on with the images I took.

The images are sort of difficult to see. I will try to improve on my photography skills before I post.

[medpretzel]

Alright,

My photography skills have not improved much since this morning.

But here you go.

The first picture are the grape wines, taken against the light. The one on the right looks so cloudy because I had moved it too much and the sediment got shifted a little.

The one on the left is the surprise rose. It's forming minute tartaric crystals, and I'm hoping that since the weather will stay cold for a few days, I will be able to precipitate out more. I tried taking some close-ups of the crystals, but it simply looks like blush-blur...

The two middle ones are my reds. (DOH!) I really can't tell if anything is going on in the demijohns, but they are cold to touch.

The second picture is a close-up of the chardonnay. This one shows that the crystals are forming, although quite discrete.

Let's hope that tomorrow morning, there will be more interesting pictures than these.

[medpretzel]

Day 4:
Temperature @ 6:45 a.m.: -7.4*C ~ 19*F

Not too many more crystals have formed. Will take pictures.

[medpretzel]

We had about a second of sun today, so I thought I'd take the opportunity and take some pics.

The crystals are so small that you need to see this in full size to appreciate that they are even there.

This is the surprise rose...

The dirty-looking specks are actually crystals that have formed on the side of the demijohn. It's NOT dirt!

Naturally, you really can't see anything going on in the reds, but in one of them, there are a few crystals floating on the surface at the neck of the demijohn. I don' t know how to interpret that, but I'm thinking that it's the tartrate again. The other red, where I did MLF, currently shows nothing. Nor does the fruit wines that I have.

So, tomorrow will be the last day I am conducting this experiment, as the temperatures are due to go up over the weekend. I will then rack and show you what is left over in the demijohns. Tonight, temps go down to -8, so that's the last of the cold-stabilisation until January, I presume.

[medpretzel]

Day 5:
Temperature at 6:45 this morning: 0* C.

I decided to rack and get the wines in.

There were crystals in all the grape wines, but none in the fruit wines.

So, I proceded to rack just the grape wines.

Here are some pictures.

1. Rose's crystals.
2. Racked the rose' into a new demijohn
3. Without knowing, the red had tartaric crystals as well. WOW!
4. Chardonnay's crystals
5. A close-up of the crystals on the side of the demijohn.