In the beginning........
Grapes ferment without help from man, Yeast spore present in the air attack the sugar in the grapes and break them down into alcohol plus CO2 plus heat (incidentally, this is the same heat from sunlight that was stored in the plant sugars during photosynthesis, and that energy from sunlight is simply being released during fermentation. Additional energy will be released again, during digestion, after we consume the wine, when the alcohol is broken down to the two compounds that were used by the plant to create sugar in the first place - water and CO2. We exhale the CO2, and, well, you know what happens to the water . . . )
.....then unless the resulting beverage is protected from air, and it can be by keeping its container full, or it's protected by a film of oil, or blanketed by a layer of CO2 or nitrogen gas......the chemical and biological process(see next item) continues to vinegar! Yuck!
The chemical process converts alcohol, via oxidation, to acetaldehyde, a nutty-tasting compound (like walnuts). A biological process, mediated by Acetobacter, the vinegar bacterium, converts alcohol to acetic acid, or vinegar (literally, sour wine, from the French, vin aigre).
Both oxidized wine and vinegar are not harmful in themselves - they simply lower the quality.
An aside - most wine is below pH 4.0 (there are some late-harvest exceptions that show up with the over-ripe fruit that is currently in vogue). At "wine pH", no human pathogens can survive. So, even if the wine doesn't taste good, it is generally safe from pathogens. Above around ph 4.3 to 4.6, the wine becomes more hospitable to human pathogens, though that doesn't mean they're in the wine.
With later harvest, and therefore high pH, fruit, several problems arise, in no particular order: SO2 is less effective; the wines are pruney or raisiny in character; the color fades and turns brown more readily; shelf life is shorter ("ageing potential"); they are susceptible to microbial problems, including spoilage micro-organisms ("ropey" wines were unheard of until the recent "blockbuster" wines came into popularity); and the wines readily lose varietal distinction.
So.....keep this in mind!
When the grapes start to develop color and soften .......verasion. usually in July. I will start checking the grapes for their sugar content which is reported as "brix" This is a percent of the soluble solids in the berries and the predominant one is glucose. Brix are measured either by a refractomer or a hydometer, typically a refractometer in the vineyard (for convenience - only a little bit of grape juice is needed), and a hydrometer in the winery (because alcohol interferes with the refractive index for sugar and distorts the measurement on a refractometer).
When the grapes are ripe the brix will typically be from about 22 brix and up. We look at other indicators of ripeness also. i.e. taste, and the browning of the seeds and dimpling of the skin. If you take your final brix times 5/9 you will have an approximate final alcohol at the completion of fermentation.
[some winemakers feel that seed browning does not correlate well with physiological ripeness, and ignore it; others put credence in it].
Many winemakers ignore the refractometer and pick on flavor ripeness - this is no different from tasting an apple, that is tart when under-ripe, and mealy when over-ripe, and absolutely delicious when perfectly ripe, with a crispy crunch and a good acid-sugar balance. Same with apricots, peaches, oranges, etc. Grapes are no different. When you walk into the vineyard and the fruit is absolutely aromatic, they are very close to perfectly ripe.
At the same time the amount of acid is dropping in the berry and the pH is rising. (the pH is the negative log of the hydrogen ion) Acids have a lot of hydrogen ions and so the connection. ( Keep in mind the grape is the plants method of reproduction) Ph and acids (tartaric, malic and citric) are important to the balance of your finished wine and its microbial stability. You, as winemaker, can manipulate the acids and the pH of your wine.
OK...time to get excited!! What will you need!
Containers to bring your grapes home in.........Depending on the amount of grapes you have ordered: a tarp in the bed of a pick-up (buy the tarp early and let it air out...plastic smells yucky) small garbage cans, large plastic boxes, large cardboard boxes...just make sure you can lift them when full and that they fit in your vehicle.
A way to crush and remove stems..... the very simplest is to crush with washed hands or feet and drain through some 1/2in square hardware cloth into a new clean garbage can. We may have a crusher/stemmer at the vineyard this year which will do this for you BUT you will be traveling home with some liquid so plan your containers accordingly. Cheese cloth or a clean sheet to cover your fermenter to keep insects out of your fermenting wine is also an essential.
Time to visit your local fermentation store..... don't wait too long or your choices might be limited.
You will need yeast and yeast nutrient....ask their recommendation based on amount of grapes, or research yeasts for Syrah on line
Yeast have different fermentation dynamics that vary from strain to strain, some vigorous fermenters, some slower. For high sugar grapes, be sure to select yeast that will tolerate the resulting high alcohol and ferment to dryness (i.e., no sugar left), lest you end up with a stuck fermenter (meaning, unfermented sugar left in the wine).
[Incidentally, the best way to get a stuck wine to complete fermentation is to bottle it. It will often re-ferment, and push the cork out or break the bottle.]
For red fermentations, ferment on the skins; for rose', ferment about 36 hours on the skins, then press off; for "blanc de noir" white wine from red grapes, crush and press immediately, then ferment.
The big problem in red fermentations is not enough heat to get good extraction (color and tannin), though Syrah typically tends to be pretty dark. Tannins give the wine ageing potential; they are a natural anti-oxidant.
A temperature of 82 to 88 Fahrenheit is typical for reds, and the fermentation should last three to five days, perhaps a little longer.
Simply fermenting reds in a 30-gallon garbage can, without auxiliary heat, will not have sufficient thermal mass to reach the mid-80s, and you will often end up with a thin, washed out red wine. An old electric blanket works well as an external heat source.
On white and rose fermentations, there typically is too much heat. Ideal is 53 to 57 Fahrenheit. Fermenting glass 5-gallon demijohns (carboys) in a bath tub of cold water will take away a lot of the excess heat.
Unless you are skilled at winemaking, it may be easiest to make a simple red wine, line a Beaujolais style, and drain the wine from the skins with full color but before all the tannins have been extracted. Then plan on drinking it within the first year.
Some potassium metabisulfite WARNING CAN BURN LUNGS! for cleaning and adding to your wine later. A hydrometer 0 to 32 and a hydrometer cylinder to measure the sugar as it is converted to alcohol. Something (paddle or baseball bat) to punch down the cap (= the skins and seeds that float on the liquid) twice a day. When fermentation is finished you will need either glass or wood containers to store your new wine. Glass carboys come in different sizes and can be bought new at the fermentation supply stores ( about $30 each for 5 gal) or used (craigs list,thrift stores garage sales.) Used barrels on Wine Country Classified, craigs list, newspapers.......be sure you know where they came from and smell the inside to look for off odors. New barrels are $$$$ You will also need fermentation locks for either your carboys or barrels.
You can press the wine off the skins through cheesecloth or rent a basket press if you have a lot.
Enough for now...your assignment is to go shopping, sign up for a class, join a group or do a lot of reading. Next topic is malolactic fermentation...to do it or not and how to clean everything! What happens with the acid and pH during and after fermentation and why and when you should add acid. How useful is a pH mter?