T/A ? YAN ? SO2 ? Brix? Specific Gravity? pH?
First let me say this. No great wine was ever crafted in a lab. Great grapes make great wines. Period. The process of understanding the profile of your wine's composition will aid you in the pursuit of crafting good wines consistently, then provide you the opportunity occasionally to make a great wine. Do I need to attend the Wharton School of Business to make sense of the numbers in winemaking? It helps to have a general understanding of what the "numbers" of a well-made Vinifera wine will look like, and why they are relevant.
First let us look at specific gravity or brix. Both are methods for measuring the volume of sugar in a liquid. Brix is a less precise unit of measure but far easier to remember in relationship to the percentage of sugar present. 1 brix = 1 % sugar in a liquid. The specific gravity scale is more precise, particularly at lower sugar levels, and is what most scientist use in a lab setting. Both scales are acceptable measuring tables.
Grape juice or must in order to craft a good wine should have at least 24 brix, or a specific gravity of 1.10 . This will result in a wine with an alcohol volume of about 13% to 14% in most cases, a good alcohol profile.
I have made wines with grapes containing brix levels as high as 31. Mother Nature enables grapes vines to ripen grapes to a maximum of 25 brix. It is not uncommon to see California grapes with brix profiles exceeding that. It is only due to the dehydration of the grapes. This vineyard practice of extended hang-time results in these elevated sugar levels and contributes to tannins developing a supple flavor profile. California has gained world wine acclaim for this "style" and has the privilege of long growing seasons to facilitate it. So whats the correct number for grapes for winemaking...? Ask 50 winemakers, you'll get 50 opinions. Personally, I like fruit at 26 brix. This ensures that acid profiles in most instances will remain in a good range and that our fruit is mature. Mature fruit serves to reduce "vegetable" or green influences that can develop in less than fully mature fruit.
pH. My favorite subject. Know this number better than your middle name. The pH of Lanza Vineyards Merlot is 3.5, the sweet spot numerical value. Vinifera grapes mostly fall into a range from 3.3 to 4.01 pH. Wines can be unstable with pH levels above 3.7 if proper sulfite additions are not made. At that pH level, microbes get frisky. You can bring your pH values into a good range through acid adjustments in most cases. It is important to understand that proper sulfite additions can only be obtained by knowing the pH of your wine.
pH meters are relatively inexpensive. Hand held units are all that are required for most home winemakers. Good models are automatically temperature compensated, can be calibrated to three points four, seven and ten. They also display readings in two decimal points.
Things can affect your pH level in the process of winemaking are primary fermentation, and malolactic fermentation. Both of these processes will raise pH values. Continue to monitor the pH of your wine through it's development, and until your bottling process is completed.
T/A or titratable acidity is a very important number in crafting good wines consistently. Red wines with a T/A ranging from 6 to 7 grams per liter are often times referred to as "well balanced" wines. White wines usually are in a slightly higher range as it serves to enhance the flavor profiles of that style. There are a number of test procedures to check your acid levels, with varying degrees of difficulty and accuracy. My preferred method can be found on our blog. Acid corrections are probably the single most important step a home winemaker can take to enhance their wines, and adjust pH. Unfortunately it is also the most often overlooked. If you are unfamiliar with the process do not be afraid. Experiment with small quantities while learning the techniques of measuring and adjusting acid. It won't take you long to become proficient at the task and it will serve you well in your pursuit to make good wines.
SO2 or sulfur dioxide is a necessary component in winemaking. Please spare me the "I don't use sulfites" speech. Every single wine ever made has some level of sulfite, as it is a byproduct of fermentation. Sulfites do not give you a headache, and you'll be fine. Use it, or drink all your wine in two months after you've made it.
Enough of that. Proper SO2 levels for your wine are predicated exclusively by pH value. The lower your pH, the less SO2 your wine will require. You can find a good table for additions based on pH on our blog. Measuring sulfites in your wine can be difficult for amateurs. The proper equipment costs at least $500.00 at the entry level. The apparatus for the "Ripper method" or "Aeration-Oxidation method" of measuring SO2 cost quite a bit more. Accuvin makes a kit for this process. Make sure the "use by" date is good when purchasing these test kits. If you are unable or unwilling to perform this type of test, here are a few "practices" that can help you.
Sulfite each 5 gallons of juice or must with ¼ teaspoon of SO2 prior to primary fermentation.
DO NOT add any SO2 when primary fermentation is complete if you plan to put your wine through malolactic fermentation. ML bacteria is highly sensitive to sulfite levels. As little as 25 parts per million may kill your expensive culture.
When ML is completed, or if not employing the ML process, add a minimum of 1/8 teaspoon SO2 but not more than, ¼ teaspoon SO2 per 5 gallons of wine at each racking and 12 hours before bottling. This will serve in most cases to ensure than some level of protection for your wine is available without using too much of a good thing.
YAN, what on earth is YAN? Yeast Assimilable Nitrogen is the new BUZZ word in home winemaking. Makes you sound like you know what your doing. ☺ It is quite simply the amount of food (assimliable nitrogen) available for the yeast cells in your juice to metabolize during primary fermentation. Having the proper levels of nutrition available for yeast while they are working prevents them from becoming stressed and inhibiting their performance. When that occurs, yeast can create unpleasant aroma and flavor profiles or just stop working or get "stuck".
So what is the correct level of nutrition required for a healthy fermentation and when do we add nutrients?
Make your additions in two stages. The first at 1/3 sugar depletion, then again at ½ sugar depletion. Assuming 24 brix prior to beginning primary fermentation, our first addition would be made at 16 brix. The second addition would then be made at 12 brix. This protocol will ensure we do not "Redbull" our yeast by providing too much of a good thing all at once.
How much nutrient required will depend on three things.
First, is the overall sugar levels present at the beginning of fermentation. The higher the sugar, the higher the nitrogen requirements. 150 to 200 milligrams per liter is the minimum required to complete a standard fermentation to 13% alcohol. When dealing with grapes above 25 brix, I recommend at least 250 milligrams per liter. When approaching 28 brix, 350 milligrams per liter.
The second factor for proper nutrition is the yeast strain you have chosen to ferment you must. Different strains have different nitrogen requirements. Familiarize your yourself with the yeast you are choosing.
The third determining factor in how much nutrient to add is your selection of and the composition of your yeast nutrient. Follow the instructions for the product you've chosen. Obtain the appropriate dosage levels to provide the correct levels of assimilable nitrogen to your must.
Numbers matter, knowing and understanding them can make a noticeable difference in your wines. Become a better wine maker. Know the numbers!