"HEAT & COLD STABILITY"

Before you get to bottling your new wines, it is essential that you know if they are "stabile".

You need to know if your wine will throw a protein haze (heat unstable) or precipitate out tartrate crystals (cold unstable).

Without making sure that your wines are heat & cold stabile, I can guarantee that they will throw deposits after being bottled. This will happen even if your wines, especially whites, are crystal clear and even tightly filtered.

It’s one thing to have so-called un-fined and un-filtered wine. It’s another thing to have hazy, unsightly wine. You could have easily prevented the problem with the following simple testing and treatment, - with no loss of quality.

COLD STABILITY. TESTING & TREATMENT:

Is your wine cold unstable? Will it throw glassy-looking tartrate crystals when chilled for serving? Or, is your acidity too high, needing to be reduced by chilling?

Tartaric (but not malic nor citric) acid is unstable at cold temperatures. If free Potassium ions (K+) are in the acid pool, they can combine with Tartaric Acid (H2Ta) to form Potassium Acid Tartrate (Potassium BiTartrate/KHTa) with a free Hydrogen ion (H+) being released.

With tartrate crystals precipitating, your total acidity lowers and your pH also lowers. Yes, that’s right, your pH also lowers because of that free Hydrogen ion, which is what a pH meter measures. The more H+, the lower the pH.

For Example: Suppose that after M/L ferment was over, you tested pH on your red wine and found that it was pH 4.0. And, you used your total acidity kit and found that your acidity was 0.6 ppt. Your guidelines recommend that a healthy red wine pH is 3.6 or below. So, you acidify with tartaric acid to bring the reading down to pH 3.6. That’s a drop of 4 points. This will also raise the total acidity 4 points to 1.0. Your acidity is now off the scale and will taste undrinkable. Then you chill the wine: The acidity drops, in this example only, to 0.7 and the pH drops to 3.3.

 

Well, at 3.3 / 0.7, the wine is going to be tight, hard, inaccessible and still acidic. Great for long term aging, but probably overcorrected for general consumption. (Remember, the lower the pH, the more acidic your total acidity appears. pH = measure of the "apparent acidity")

So, let’s say we only correct to 3.7 / 0.9 (3 points). Then chill, dropping the acidity to about 0.7 and the pH to about 3.5. The wine is now cold stable and tastes rich and accessible.

Since we now see that pH lowers with chilling & precipitation of tartrates, be conservative and correct to above the desired pH. This is only an isolated example. Your wine will correct itself relative to K+ concentration and the effectiveness of your chilling operation.

PHYSICAL CHILLING TECHNIQUE:

Any treatment less than the above will take more time and will remove less tartaric acid, possibly not achieving cold stability.

A cold cellar, over a cold winter, often will do the trick. This is a good reason for doing acid corrections soon after crush. If it's now warm in the cellar, some sort of refrigeration will be required.

Caution: Cold liquids more easily absorb oxygen. Do not splash etc.. Completely top up containers. Warm to room temperature before racking wine off of tartrate deposits. Maintain proper SO2 levels.

TESTING FOR COLD STABILITY:

 

HEAT STABILITY: TESTING & TREATMENT

Heat/Protein stability is a question in white wines. The skin tannin content in red wines attracts protein, usually resulting in a natural finning/stability. However, whites require the use of Bentonite to remove unstable protein fractions. Bright, even tightly filtered whites will almost always throw a fluffy protein haze after bottling if not treated. This is often also seen in white fruit wines.

Each wine has a multiple set of protein fractions. They vary from year to year, microclimate, cultivar and wine variety. Each protein fraction has an "iso-electric point". If this point is within the pH of your wine, that protein fraction is unstable. It will precipitate when the wine warms, as in after you bottle. (more details on request)

So, how much Bentonite do you add to achieve heat stability? Too much generates excess lees and wine loss, and might strip flavor & color. Too little leaves your wine still unstable. The home package of Bentonite calls for ½ teaspoon per gallon. This is about 3 lbs per 1000 gallons. That’s a common average for some Chardonnays but may be one-half what you need for Sauvignon Blanc. And, as mentioned, last year’s amount may not be correct for this year.

The trick is to use the least amount to get the job done. You must test for heat stability. Fortunately, it’s a relatively easy test. Considering what you’ve spent on fine grapes with the anticipation of fine wine, a little attention to detail is well worth it.

TESTING FOR HEAT STABILITY:

You could boil a sample, cool and see if a haze and/or deposit forms. This is overkill. Your wine will never see those conditions and you’ve just precipitated out all protein fractions, not just the ones most unstable at wine pH. If you’re just going to do this, you might as well use the standard ½ tsp per gallon and skip ahead to the bus trip.

#1- Make a 5% Bentonite Solution: To 5 grams Bentonite granules, add water up to the 100 ml mark. This needs to be done the day before use. See below for complete preparation procedure.

#2- To 100 ml samples add:

If you do not have a gram scale, here is a teaspoon conversion table:

1/8 tsp = .9 grams; 1/4 tsp = 1.7 grams; 1/2 tsp = 3.4 grams etc.

#3- Mix and let stand at least overnight. Carefully decant (swinex hand filter is best) clear sample into another test tube. Incubate at 140° F for 24 hours. I use a water bath in an electric skillet.

#4- Refrigerate for several hours and then let stand at room temperature overnight.

#5- Observe: A precipitate is read as very unstable. A cloudiness as unstable. A slight haze as marginally unstable. Possible interferences are precipitated pigments, yeast growth, and residual Bentonite from incomplete filtration/decanting. Just calculate backwards for the volume you are treating.

e.g.: 6 lb/1000 gal = .03 lbs/5 gal = .48 ozs/5 gal.

Note: Do your tests in a manner similar to what you’ll do in the cellar relative to making the Bentonite slurry and mixing it in the samples.

PREPARING BENTONITE: Very, very slowly, add the Bentonite powder into hot water, stirring well. It will still clump-up, being a clay from Benton, Wyoming. Refrigerate overnight. (Time is needed for the Bentonite "plates" to "un-stack" exposing the multiple negatively charged facets that attract the positively charged protein). Then mix until it is a thick but creamy slurry. A blender/mixmaster works great here - if it doesn’t get you kicked out of the house.

Note: We now carry "agglomerated" Bentonite that does not need to be refrigerated overnight. Just dissolve and use.

 

ADDING THE BENTONITE SLURRY: Again, try to simulate the mixing you did with the test samples. As with all finning agents, the Bentonite must get mixed instantly and thoroughly. Easiest for home amounts is to rack the wine and add the slurry at ¾ full. It will mix itself, clouding the whole container.

An addition of Sparkolloid after the Bentonite works well to take out negative charged particles. It also somewhat collapses the Bentonite stack and packs down the fluffy slurry. Add the warm Sparkolloid slurry just as you get to the top of the container, right on top of the just added Bentonite. Wait as long as you can for the stuff to pack down, minimizing wine loss. Minimum time = 2 weeks.