Making a Yeast Starter

Preparing a Yeast Starter

It is easy to make a yeast starter and I want to make the starter as soon as possible.  The reason for this is that in this part of Greece where it is still quite warm when the wine grapes are ready for processing, the wild yeasts that are naturally on the grape skins can get a head start and begin their own fermentation.  I do not use sulfites in the must to kill the wild yeasts, so I want my wine yeasts to be ready for inoculation as soon as I have finished the initial tests and corrections that I do on the must.

Packets of Wine Yeasts

Once I have collected about four to five quarts of grape juice from the pressing, I place the juice in a stainless steel pot and bring it to a boil.  Once the juice cools to body temperature or below I inoculate it with a 5 gram (0.176 oz) packet of wine yeast such as Premier Cuvee or Montrachet.  In about 6 to 12 hours, the pot of inoculated grape juice will be foaming with the activity of the yeasts and it will be ready to use to inoculate the rest of the must.  This quantity of yeast starter is enough to inoculate one to five primary fermenters filled with 50 liters (13+ gallons) of must dividing it proportionately.

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Measuring Sugar in the Must and Making Corrections

When I make wine, I want the sugar content of the must prior to fermentation to be at or very near 24% sugar.  Once the juice is collected, the easiest way to measure sugar content is to use a refractometer (also known as a Brix Refractometer) that is designed for the purpose and has a range of 0 to 32% Brix (in other words 0 to 32% by weight of sugar in a solution).  This instrument can be purchased at a wine supply shop or on line.  These days they are not as expensive as they once were, and for measuring sugar they are convenient, easy to use, and come in at least two types.  In one type the instrument's readings are self correcting for temperature and in the other type they are not but need to be corrected by the user if the temperature of the must at which the reading is obtained differs from the temperature for which the instrument is calibrated.  The one that I use is calibrated for 20^oC (68^oF); therefore, I need to correct the readings I get if the temperature differs from this value, but that is easy to do.


I take a sample of the freshly pressed grape juice, and using the refractometer and a thermometer I record the percent sugar in the must and its temperature.  (A good quality refractometer from a reputable supplier like Fisher Scientific comes with excellent instructions for its use.)  As an example, the Muscat grape juice that I talked about in the previous blog gave a reading of 23.2% at 28^oC.  At this temperature a correction of 0.62% to 0.63% needs to be added to the reading giving 23.8% sugar in the must.  For me this is close enough to 24%, and no sugar addition is needed.


Things are a little different when the sugar content of a grape juice is above 24% as was the case for this year's (2013) rose' made from Merlot grapes.  When I measured the sugar content of the rose' must I got a corrected value of 25.6% at 27^oC.  This is too high and would result in high alcoholic wine if allowed to ferment to dryness.  An easy remedy is to add to the must tap or spring water never distilled water; but how much to add?  To answer this question requires a little work, but not much.


An approximate method for figuring out how much water to add is to do this simple arithmetic:

1. divide the % sugar in the juice by the % sugar that I want,
2. multiply the result in 1. by the total volume of must,
3. the result of 2. is the new total volume of must after the addition of water,
4. subtract from 3. the original volume of must that I had,
5. and the result of 4. is the volume of water to add.

In the case of my rose' must here are the results:

1. 25.6/24 = 1.067,
2. 1.067 x 55 = 58.7 liters which is almost 59 liters,
3. 59 liters,
4. 59 - 55 = 4 liters,
5. and 4 liters of water must be added to the 55 liters of must.

So here's what I did, I added 4 liters of water to the 55 liters of original must.  After a thorough mixing as a check I took a sample, measured its percent sugar and its temperature.  The uncorrected percent sugar was 23.6 at 27^oC and 24.1% when corrected for the temperature.  This is close enough to the target of 24%.  Notice that this method is approximate and underestimates the amount of water to use, so if I don't quite make the percent sugar I want I can add a little more water.  Incidentally, this method works for gallons as well as liters, too.  I just substitute gallons for liters in the calculation.


That's all well and good, but what happens when a grape juice has a lower reading from 24% for sugar; what do I do?  Actually that's what happened with this year's (2013) Estate Rose' must.  I got a corrected 22.9% sugar in the 35 liters of must.  To say that a juice has a 22.9% sugar content is to say that for every kilogram of juice there is 0.229 kilogram of sugar in it (or for every pound of juice there is 0.229 pound of sugar in it).  But I want a juice that is 24% or 0.24 kilogram of sugar per kilogram of juice.  Here is what I do to make the correction:

1. I subtract from my target percent the percent that I have,
2. multiply the result of 1. by 10,
3. and multiply the result of 2. by the total volume of must in liters.

In the case of my Estate Rose', here are the results:

1. 24.0 - 22.9 = 1.1,
2. 1.1 x 10 = 11,
3. and 11 x 35 = 385 grams of sugar to add to the must.

After adding 385 grams of sugar to a portion of warmed must and stirring it until it completely dissolved, I added it to the remaining juice and mixed it in well.  The corrected refractometer reading for this must after the addition of the sugar gave 23.7%, close enough to the 24% that I want.  Once again this method underestimates the amount of sugar to add, and that is a good thing.  Once the sugar is there, I have to live with it.


When I am measuring volume in gallons (US) and weight in ounces I multiply the result of 2. above by the total volume in gallons and the factor 0.1335.  So, in my case since 35 liters is the equivalent of 9 and a quarter gallons (9.25 gallons), the calculation becomes 11 x 9.25 x 0.1335 = 13.6 ounces of sugar to add to the must.

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Making Dry White Wine and Dry Rose' Wine

Heading Out to Get the Grapes

Muscat and Merlot Grapes

Generally each year, I make a red, a white, and a rose' wine, and I make these from different varieties of locally grown grapes.  Even though a white wine can be made from deeply pigmented grapes, I usually start with a white grape variety.  For me the basic recipe for making a white or a rose' wine is simple:  the grapes are gathered, crushed, pressed and the resulting juice is placed in a primary fermenter, analyzed, corrected for faults, and inoculated with a wine yeast.  The few analytical methods that I use will be found in this blog under different titles.  For example, in two previous parts of this blog, I describe how to measure the alcohol content of wines:  one is titled Measuring Alcohol Content in Wine by the Potential Alcohol Method and the other is titled Measuring the Alcohol Content of Wine.



Helping Hands

In this northeast region of Greece, the Muscat and Merlot grape varieties that I use ripen in the last week of August, and that means packing up the car and trailer and heading off to the grape farmer to get them.  I usually buy 200 kilograms (440 pounds) of each grape variety.  Once home, the real work of processing the grapes begins, and it is great to have an extra pair of hands to help.  I always work with grapes and make my own juice for fermentation.


Before I work on the grapes, I get the press and grape crusher ready.  Once set up and in place, the inside basket of the press is lined with clean plastic window screening.  This is done to prevent grape matter from seeping or shooting out under high pressure during pressing.




Loading the Crusher

I usually make my white Muscat grapes first. I crush the grapes and put them into the press stems and all.  Some grape suppliers at slightly extra cost will crush adnd remove the stems of the grapes for you, and believe me that saves a lot of hard labor.  Once full, the pressing begins, and the juice that is produced is placed in translucent plastic barrels on which I have marked volume heights.  When no more or very little juice flows from the press, it is opened, the mass of skins is loosened, and re-pressed.  Loosening the mass of skins in the press is repeated two or three more times.  In addition to getting more juice out of the grapes, there is at least one more good reason for re-pressing the mass of grape skins. 

Loading the Press

The white wines and the rose' wines that I make are fermented off of their skins (the skins are not present during fermentation) and as a result will be low in the tannin they would otherwise extract from the skins.  Tannin is necessary for a healthy fermentation, and by re-pressing the skins two or three times, more of these vital tannins are extracted into the juice.  Of course, tannin is available at wine supply shops and can be added without the need for re-pressing.  In this case, just follow the instructions that come with the tannin.

 

Once the juice is in the plastic barrels and I know the total volume of must that I am dealing with, it is necessary to analyze the must for its sugar content and total acidity.  Based on the results of these anualyses, I will or will not make adjustments just before I inoculate the must with a wine yeast to start fermentation.

Pressing Rose'

To make rose' I follow the same recipe that I use for whites except that I use the Merlot grapes or another red grape variety.  Usually, I process approximately half of the Merlot grapes that I get into rose' wine.  So, re-pressing the crushed red grapes two or more times not only extracts the tannin needed for a healthy fermentation, but it also extracts more color from the skins to give the titled wine its hue.


The preparations and analyses that I do prior to the start of fermentation are few and simple.  They are, in the following order:

• begin a yeast starter,
• do a sugar analysis and make the necessary corrections,
• determine the specific gravity of the corrected must and its temperature,
• do a total acid analysis and make the necessary corrections,
• measure the pH of the corrected must,
• and inoculate the must with the yeast starter.



Primary Fermenter

Once the must is inoculated with the yeast starter, I leave it in the primary fermenter, a large 70 liter or 18 gallon food grade plastic container, for three to four days or until major foaming of the must stops.  I make sure that there is ample space above the surface of the must in order to prevent the foam from overflowing.  This usually means not filling the primary fermenter to more than three quarters of its volume.  Once I'm sure that major foaming is finished, the fermenting must is transferred to large 20 to 25 liter or 5 to 7 gallon glass containers each fitted with a rubber stopper and fermentation lock.  The fermentation lock is partially filled with water which prevents air from entering the jug, but allows carbon dioxide to escape.  Again I leave some space to accommodate foaming before filling the jugs to 4 or 5 inches below the fermentation lock.

Over the next 10 days or so fermentation will gradually slow considerably and large deposits of solids consisting of some tartrates but mostly dead yeast cells will form on the bottoms of the glass bottles.  (See the video above)  When this happens it is time to decant the must into clean jugs where fermentation will slowly continue.  This process of decantation which I do using a syphon pump is known as racking and is done in a way so as to disturb the sediments as little as possible.  As the fermentation slowly progresses noticeable deposits of white potassium acid tartrate, also known as cream of tartar, will form on the bottom of the jugs, and I will repeat the racking in about two weeks.  The formation of these tartrates happens because this salt of tartaric acid is not so soluble in the essentially alcohol and water solution that is slowly becoming wine, and the wine is slowly losing acidity.  After this second racking I will continue to rack the wine every two months or less until I am ready to filter the wine in preparation for bottling it.  I talked about filtering the wine and its value in a previous blog called Filtering the Wine.



Measuring Alcohol Content in Wine by the Potential Alcohol Method

In an earlier blog, Measuring the Alcohol Content in Wine, some of the general points are covered relative to the alcohol content of wines and the various methods for its measurement.

Specific Gravity Materials

I use the potential alcohol method to measure the alcohol content in my wines.  This method is simple and it gives acceptable results.  First, I set up the area where I am going to do the measurement by bringing together in the same space the wine or must, the hydrometer, the transparent cylinder that I will use, and a thermometer.  The cylinder will contain the wine or must and the hydrometer.  These items are left for about three or four hours before making any measurements so that they are all at pretty much the same local temperature.

When I am ready to measure potential alcohol (see the video above), I place the hydrometer into the cylinder holding it by its upper tip.  I add the wine/must to the cylinder until the hydrometer floats, give the hydrometer a spin to get rid of bubbles that might be adhering to the glass, and let it come to rest on its own.  When the hydrometer stops moving and is floating freely not touching any part of the cylinder, I record the specific gravity reading.


As an example, for the rose' must, I measured its specific gravity on August 31, 2012 (using the hydrometer calibrated at 60^oF) and got 1.106 at a temperature of 27^oC (80.6^oF).  At this temperature the specific gravity requires a correction of 0.002 to be added to the reading giving 1.108 as the corrected specific gravity.  According to the table of potential alcohol for this specific gravity reading a wine of 14.2%  potential alcohol by volume should result.  On August 9, 2013, almost one year later, I measured the specific gravity of the rose' wine that this must produced and got 0.992 at 28^oC (82.4^oF) which requires a correction of 0.003 giving 0.995 as the corrected specific gravity.  But this reading is below 1.000 which indicates that all the sugars have been consumed and this is an essentially dry wine of 14.2% alcohol by volume.  If this had not been the case, the latter potential alcohol reading would be subtracted from the former to get the alcohol content:  14.2% - 0% = 14.2%.


Potential alcohol tables are readily available on the internet along with detailed instructions for their use.  Just use the search terms potential alcohol table and you will get a long list to choose from.  In fact, the hydrometer that I use came packaged with instructions for its use along with a potential alcohol table and instructions for making temperature corrections to specific gravity readings.

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