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Testing the must for sugar content, PH, and TA

05/09/2012

Before you add the yeast, you need to test the must to determine if any additions/corrections are needed. Very rarely will you get a grape that naturally has the required balance of acids, sugars, and pH necessary to create a harmonious wine. When one or more of these elements are out of their ideal ranges, the quality of the wine suffers. Any potential the fruit had to make a nice wine is significantly lowered. However, if we take the time to correct any possible problems and balance the must early on, the quality of the resulting wine will be better maintained.   Correcting a must lays the foundation on which the wine will be built. Even slight adjustments can raise a wine from being just good to great.  
 
*Note: When making corrections, consider the varietal. Seed/skin to juice ratio varies for each grape.  We will only be getting around 3 (Bordeaux) to 3.5 (Zin and Rhône)* gallons of finished wine from every 5 gallons of must! This comes out to 60-70% of the must volume. Don’t forget to take this into account when making corrections to the sugar levels or pH/Total Acidity (TA).   In addition, most products designed to go into the must should still use the entire must volume to calculate their dosage. This compensates for the portion of the additions that physically bind to the must itself and will not make it into the final wine volume.  This includes SO2, enzymes, tannins, oak, Opti-Red, Booster-Rouge and Noblesse. 

* Common examples of Bordeaux grapes are Cabernet Sauvignon, Cabernet Franc, and Merlot. Rhône varietals include Syrah, Grenache, Mouvèdre, and Pinot Noir.  

Test the Sugar:  
Before making any adjustments, double-check your °Brix after the grapes have been crushed and the must has had a chance to be completely mixed together. There is usually a bit of variation in sugar levels between each and every bunch of grapes that make up the whole volume. Interestingly enough, these differences are not only found in fruit coming from different sections of the same vineyard, but even off of the same vine. Therefore, the only way to get a truly accurate sugar reading for any must is to wait until the fruit has been completely processed and thoroughly mixed together.  
 
*Note: Testing the whole must also helps to make the TA and pH testing more accurate as well. (Information on TA and pH and why they are important will be explained shortly)  
 
 
You can measure the sugar level with a hydrometer or a refractometer
 
A hydrometer works by measuring the density of the liquid you're testing compared to water at a certain temperature.  Temperature affects density, so it is important to have a sample close to your hydrometer's calibration temperature.  If using a hydrometer: make sure to strain the sample of juice to remove any seeds and skins before filling the hydrometer jar. If the solids are left in the sample, these may cause the hydrometer to stick to the side of the jar, compromising the accuracy of the results. Another good technique for getting a clear juice sample is to place the sample in a freezer for 15-20 minutes.  Decant off of the sediment that settles out. However, because a Hydrometer works off of the principle of density, and  density changes with temperature, you will need to allow the sample to warm back up to 68 F before the results will  be accurate because this is where most hydrometers are calibrated. The hydrometer jar should contain enough sample that the hydrometer is always floating. Wait until it stabilizes and read the number where the top of the liquid meets the scale on the hydrometer.  
 
Note: Depending on the temperature of the sample, you should also add or subtract the amount indicated by the thermometer at the bottom of the hydrometer for the greatest amount of accuracy.  
 

If using a refractometer, add a drop or two of the juice to the lens and close the flap onto it. This will cause some of the juice to squish out, which is normal. Next, wait 30 seconds for the sample to adjust to the temperature of the refractometer prism. Then, hold it up to the light and look through it to see where the colored bar extends to on the scale. This is your ºBrix reading.  
 
When using a refractometer, make sure the glass lens is clean and dry, and reads 0 ºBrix when testing with plain water. If not, adjust/calibrate it with water according to the instructions that came with it. This usually involves turning a knob or a small screw while looking through it until it reads “0”.  
 
Once you have gotten a ºBrix reading for the must, record this in your notes and determine if you need to adjust the sugars or not:  
 
As mentioned earlier, you want a sugar level of 22°-25° ºBrix for the start of a red wine fermentation.  
 

  • If your sugar level is lower than 22° ºBrix, we recommend adding sugar to bring it up to the standard level (called chapitalizing the must). This is done with table sugar: 1.5 oz. of table sugar per US gallon of projected liquid raises the ºBrix by 1°. Measure the amount of sugar needed and completely dissolve it into a small quantity of warm water The warm water ensures that the sugar will dissolve completely into the wine. This small amount of water will not be enough to dilute the wine. Alternatively, you can dissolve the sugar directly into the liquid from the must, but depending on how much you are adding, this may be difficult. Mix thoroughly into the must so that the sugar (which is heavier than must) doesn‟t wind up sitting on the bottom of the fermentation vessel.  
     
  • If your sugars are higher than 25 ºBrix, you may choose to leave the must as is and make a “big” wine. However, depending on your yeast strain, you may get a wine that does not ferment all the way “dry” (less than 1% residual sugar). To avoid this, you can dilute the juice to 22°-25° ºBrix with water.  

 
For complete notes on dilution and chaptalization, see our guide to Dilution and Chaptalization of Musts


 
If you don‟t have a scale (MT351): 1 tsp of table sugar = 5 grams (.17 oz.)  
                                                  8.8 tsp of table sugar = 1.5 oz.

TA and pH  
The next two sections deal with testing pH and TA. These are very important elements to monitor during winemaking because they give us an indication of what is going on with the overall balance of the wine. TA measures all of the combined acids in the wine, (there are many different types) and tells you how acidic/tart the wine is. TA is expressed in either %TA or in g/L of Tartaric Acid. For example, a wine‟s TA could be expressed as 0.65% TA or as 6.5g/L TA. These two values are equivalent, and you can easily switch between the two common ways of expressing TA by moving the decimal point one place left or right. We prefer to express TA in of g/L because we feel it is easier to visualize: We are literally saying that the wine has 6.5g of TA per L of wine. The pH is a measure of how these acids balance out against buffering compounds such as Potassium. pH value also indicates how effective the blend of acidic and basic compounds will be at helping to protect the wine. pH is measured in pH units, pH values of less than 7.0 are acidic. The typical pH range for red wines is between 3.5 and 3.8.  
 
Let's take a look at how these two parameters interact. Assume we have two red wines that each have the same TA, but different pHs, 3.2 and 4.0 respectively. The wine with a pH of 3.2 will have bright fruit flavors, but it will also be thin, acidic and aggressive on the palette. On the other hand, the wine at 4.0 will be softer and rounder than the wine at 3.2, but also less vibrant; the fruit characteristics will flatten out quickly. Ideally, we are after a wine that has the freshness and strong fruit characteristics of the lower pH wine, but with the roundness and approachability of the higher pH one. The key to achieving this lies in making sure the pH of the wine ends up somewhere in the middle of these two extremes, between 3.4-3.65 pH. Vigilant monitoring of your TA and pH will help you achieve this goal.  
 
The importance of correctly preparing a sample for both the TA and pH testing: TA and pH are sensitive tests. It is important to properly prepare samples or we may get false results. With red wines, it is best to get a sample of the must and lightly run it through a blender. The blender serves to open the skins and simulates the chemical make-up the juice will attain once fermentation has completed.  The blended sample will need to be strained because the grape solids all have a different pH and TA than the juice itself. If they remain in the sample, they can skew the results. We only want  to test the final liquid that is free of solids. To achieve this, first strain the blended fruit to get the solids out. A fine mesh bag (Bag10) is great for this. Next, filter the resulting liquid to obtain a clean juice free of particles. (Paper coffee filters pushed into a wine glass are great for this). The resulting clean juice is optimal for TA and pH determinations.  
 
Steps to prepare sample:

  1. Lightly blend must in a blender  
  2. Strain blended must through mesh bag into a bowl or jar to remove solids. Lightly squeeze bag if needed until enough sample has been collected: 50-100mL  
  3. Place coffee filter part way into a wine glass or jar (maybe use rubber band to secure it around the rim to keep it from falling in.) Pour sample into the filter and allow it to drip into the glass/jar: 30-50 mL. Use this sample to do the pH and TA testing on.

Test for the Total Acidity%  

There are three methods used by the home winemaker to test for acidity:  

  • Method 1 – Basic: Test the must with an acid test kit (W501).  
     
  • Method 2 – Better: Use a pH meter with our Test Kit (W501). Run the same test using the acid test kit from the first method, only this time stir with the pH meter while titrating until it reads pH 8.2. Use this as the endpoint for the test in place of the color change. Calculate the results by following the acid test kits instructions exactly as in the first method.  
     
  • Method 3 – Best: Use the Hanna Acidity titrator (MT682). This is a machine that takes 30 seconds to give you a highly accurate TA reading. Great if doing large batches of multiple samples. Used by hundreds of commercial wineries.  

 
Once you have tested your TA, you can decide whether it needs adjusting. Keep in mind that that wine chemistry is very complex. Often, the amount of acid we have calculated on paper is not the amount that winds up being the best choice for taste. This is especially true when working with larger acid additions (>.2%TA or 2 g/L). We recommend making ½ of the addition you think is needed, and then test and taste to see if the balance is correct or if the wine still needs more acid. This is definitely one of those times where art and science come together. Ideally, we are looking for the must to be in a range of .60-.90 TA at the start of fermentation.
So:  
 

  • If your acids are in the .9%-1% range, you will want to consider lowering them. One of the best ways to do this is a MaloLactic Fermentation, or “MLF” after the primary, alcoholic fermentation has finished (for more complete information on MLF, see our Guide to Malolactic Fermentation)
     
  • If your TA is significantly lower than .60%, you will need to raise it at least to this level by adding tartaric acid. Calculate the amount needed to raise your volume to the desired acidity level (remember to factor for just the juice, not the whole must). Dissolve it completely into some wine or warm chlorine-free water and mix it thoroughly into the must/wine.  

 
3.8 grams Tartaric Acid per US Gallon raises TA by +.1% (1 g/L)
 
If you don't have a scale:  
1 level teaspoon Tartaric Acid per US Gallon raises TA by +.12%  
1 tsp Tartaric acid = 5 grams.  

For in-depth information on acidity and adding acid to a must, see our Guide to Acidifying Must.
For a complete example of adjusting the TA of a must, see our Complete Must Adjustment Example.

Check the PH:  
A general fact that might be helpful when taking a wine‟s pH into account is the higher the acid, the lower the pH. So, if your pH is high and you need to make an acid adjustment, the acid will also help to bring your pH down. The inverse is equally correct: if your pH is low, then lowering your acids (with a cold stabilization, chemical adjustment, or MLF) will raise your pH.  
 
Optimally, the pH of a red wine should be in the 3.4-3.6 range. A pH above 3.6 indicates and unstable wine and will not have a long shelf life. pH under 3.4 generally indicates a wine that will be too sour. If you have a pH meter, now is the time to use it! If you do not (MoreWine! has a variety of models to choose from), it is probably safe to say that if your TA and sugars are at their correct levels, then your pH level is fine. However, be careful in years where you see rain on the vines just ahead of harvest, as this can cause the vine to leech additional buffers – compounds which interfere with an acid‟s ability to express itself in terms of pH – from the soil as a result of the rain. This often yields higher pH values than would be expected for a given TA value. Testing with a pH meter is always the best way to be certain.
 

For in depth information on pH adjustments, see our Complete Must Adjustment Example.

To view our VinMetrica Three-in-One Testing Unit, click here.

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