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Wine - The Theory of Winemaking
About this hub
This hub explains home winemaking. When you understand the processes, you will be able to design your own 'recipes', (though, as we'll see, 'recipe' isn't really a word that applies to winemaking). If you have never made your own wine and just want to get started, I'd recommend my beginner's hub, How to make Wine from Supermarket Grape Juice without buying Special Equipment. First get a brew on the go, then come back here and read the theory!
The alcohol produced during pulp fermentation extracts colour from the skins. True red wine can't be produced any other way, as the colour in red (black) grapes is mainly in the skins, not in the pulp. At the same time, tannins are extracted. These help preserve the wine as it ages, but can also make it quite unpleasant if drunk too young. Tannins are very astringent in the mouth. Think of stewed tea and the way it dries the tongue and teeth. Not nice. In general, pulp fermented wines are more complex in flavour and aroma, but harder to control and slower to mature.
Wine from Juice and from Fruit
Most people know that wine is fermented grape juice. We'll look in detail at fermentation later. First, let's talk about the two distinct methods of dealing with the grapes:
Method 1, Juice Fermentation - the juice is obtained from the grapes, usually by pressing, and the skins and pips discarded. The pure juice is then fermented into wine. Most white wine is made this way.
Method 2, Pulp Fermentation - the grapes are crushed to a pulp, which is allowed to ferment for a few days before pressing out the now strongly fermenting juice. Most red wine is made this way.
Juice fermentation is much easier to control and to understand. And as it produces wine that is ready for drinking sooner, it is the better choice for the beginner. So, we'll leave pulp fermentation for another hub.
Adjust the Must!
The sugar in the must raises its specific gravity (SG). Water has a SG of 1.000. A wine must will typically have a SG of around 1.080. This is the equivalent (approximately) of 200 grams of sugar per litre, or about 2 pounds per gallon.
If you were making wine from vegetables (some people do!) you could simply add 200 grams of sugar per litre every time, because vegetable juice is almost sugar free.
Fruit juice is trickier, because it already contains some sugar, but how much? Winemakers use a hydrometer to measure the SG of the must, then work out how much extra sugar to add. The hydrometer is just a weighted hollow tube which floats upright in the must at a depth that depends on the SG. It is very easy to use, and no serious winemaker is without one.
If you don't want to use a hydrometer, a rule of thumb is:
- For supermarket grape juice, add approx 100 grams per litre
- For non-grape fruit juices, increase this to 150 grams per litre
- For vegetable juices, add the full 200 grams per litre
Professional winemakers (and dedicated amateurs) check the acidity of the must by a process called titration. This determines the total amount of acid present, and is not the same as measuring pH, which is more a measure of the strength of the acid. A typical wine must will have a total acidity in the range 3.5 to 5.0 parts per thousand, with white wines generally higher than reds.
Acidity measurement and adjustment is one step too far for many amateurs. Fortunately, it isn't always necessary, if you follow these guidelines:
- Don't make wine with pure citrus fruit juice - it is too acidic
- Most grape juices will make acceptable wine without adjustment
- Always add lemon juice to vegetable musts - vegetables are almost acid free.
A Good Must
What is a must?
The must is the name winemakers call the juice that is to be fermented into wine. Isn't that just a fancy name for juice? Yes and no. There are very few juices that will produce a good wine all by themselves. Most juices will be 'out of balance' in some way and will need adjusted before fermentation.
It is the sugar in the must that converts to alcohol during fermentation. Too little sugar and the wine will be too weak. Understrength 'wine' barely tastes like wine at all, and is likely to go off, without enough alcohol to protect it from spoilage organisms. But too much sugar is equally bad. Carefully managed, it can produce a strong sweet dessert wine, but in practice it is quite likely to stop fermenting early, resulting in a weak, syrupy 'wine' suitable only for pouring over ice cream.
Fully ripened grapes can sometimes yield a must that contains enough natural sugar to produce a table wine. But most juices, whether purchased from a supermarket or expressed from your own fruit, will benefit from adding sugar before fermentation. Use ordinary white granulated sugar, dissolved in water to make a sugar syrup.
Acid Content (total acidity)
Don't panic - this isn't difficult! Yeast is a living organism and can only thrive in its prefered environment. A must with too little acid might stll ferment, but will produce many unpleasant tastes and smells. Too much acid is less harmful. The result will usually still be wholesome, but it will have that sharp taste sometimes found in low quality white wines, especially from colder countries like Germany.
Grapes contain natural tartaric and malic acids. Apples contain mainly malic acid, and citrus fruits contain citric acid. Even if you don't want to measure the acidity of a must, you should always taste it before fermentation. Acid gives a sharpness to the taste. A must that is low in acid will have a flat, puddingy taste. Adding fresh lemon juice is a quick and easy way to increase acidity if you feel uncomfortable dealing with powdered tartaric acid.
As a general rule, white wine should be more acidic than red, and totally dry wines less acidic than sweeter ones, where the extra acid balances the sweetnes and lends a freshness to the taste.
Control the Fermentation
The key to success is to look after your yeast. Yeast is a living organism. Treat it well and it will repay your kindness tenfold.
- a balanced must (see above)
- an even temperature around 22C (72F)
- direct sunlight
- hot, cold or very varied temperature
Yeast Starter (phase 1)
- add yeast to about one tenth of the must
- shake well to aerate it
- keep it warm and out of the sun
- after 24 hours add to the main must
Main Fermentation (phase 2)
- maintain steady temperature
- no direct sunlight
To Finish (phase 3 end)
- place in refrigerator for 3 days
- sediment settles
- wine falls clear
Stabilise and Mature
Yeast activity may be over, but that does not mean the new wine is stable. If you intend to drink the wine within weeks, that's fine. Young juice wines can be very palatable. But if you want to mature your wine, which is the only way it will reach its full potential, it is not sufficient just to stash it away and hope for the best. However, maturing is a topic in its own right, and will be the subject of another Paraglider hub. Thanks for the read!
I learned winemaking in the early seventies. After much trial and error, I read two great books which steered me away from recipes and towards understanding:
- Scientific Winemaking - Made Easy, by J R Mitchell
- Progressive Winemaking, by Brian Adam and Peter Duncan
I like to think that if any of these excellent gentlemen ever read this hub, they would acknowledge that I have remembered at least a little of their teaching. Cheers!
Yeast and Fermentation
Don't let anyone tell you you can make wine without yeast. If you don't add your choice of wine yeast, the must will 'ferment' under the control of some airborne (or flyborne) wild yeast. The results will be unpredictable at best, and quite probably undrinkable or even dangerous to health.
A wine must is a perfect breeding ground for micro-organisms and will be colonised by the first arrival. If you make sure this is your wine yeast, it will take over the must and effectively exclude all competitors.
Fermentation - the basics
During fermentation, the complex sugars in the must are broken down to simple sugars, maltose and dextrose, which are in turn converted to alcohol (ethanol) and carbon dioxide. Strictly, it is not the yeast itself that does this, but enzymes released by the yeast. The process is in three stages:
1. Growth Phase (Aerobic)
The yeast cells multiply rapidly in the must, in the presence of oxygen. Winemakers talk about 'starting the yeast'. The yeast is added to a small quantity of the must and shaken vigorously which helps to hydrate the dried yeast and also dissolves oxygen in the must which the yeast uses in replication. Not much alcohol or carbon dioxide is produced during this stage, which typically lasts for a day or two. The active starter is then added to the bulk of the must which it proceeds to colonise.
2. Main Phase (Anaerobic)
Once the yeast has used up the dissolved oxygen, the main anaerobic phase begins. Enzymes released by the yeast cells cause the breakdown of sugars in the must to form alcohol and carbon dioxide. After a few days of extremely vigorous fermentation characterised by a heavy frothing, the processes slows down to a steady bubbling, which will last two to three weeks.
3. Decay Phase (Anaerobic)
Eventually, the fermentation slows down to the occasional bubble, or stops completely. There are two good reasons for this:
- All the dissolved sugar has been converted to alcohol. With no 'food' left, the yeast dies
- There is still some sugar left, but the must now exceeds the yeast's alcohol tolerance. This typically happens around 13% alcohol by volume (ABV) though this depends on the yeast variety
Occasionally, fermentation can stop early, but this shouldn't happen with a good yeast and a balanced must.