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Wine - The Theory of Winemaking

A scientist turned engineer, Dave started making wine in 1970. His approach combines simplicity with sound scientific principles.

About this article

This article 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 article, How to make Wine from Grape Juice. First get a brew on the go, then come back here and read the theory!

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.

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.

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 article and focus entirely on the juice method.

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.

Sugar Content

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.

Adjust the Must!

Sugar First

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

Acid Adjustment

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:

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  • 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.

Yeast and Fermentation

Wine Yeast

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.

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.

Yeast enjoys:

  • a balanced must (see above)
  • an even temperature around 22C (72F)

Yeast dislikes:

  • 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 article. Thanks for the read!

My Sources

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 article, they would acknowledge that I have remembered at least a little of their teaching. Cheers!

  • How to Make Wine From Grape Juice
    Also by Paraglider, this article takes you through the steps of making your own red or white table wine, using a minimum of equipment and no chemical additives.

Comments, newest on top

Dave McClure (author) from Worcester, UK on September 03, 2020:

Hi Pam - when scaling up, the rule is, scale up all the quantities, but don't change the times. So, for 23 litres, multiply all the weights and volumes by 23/5, or 4.6. It will work just fine and will take the same length of time to make.

Pam on September 03, 2020:

Thank you for a great guide to wine making, I have made the 5 litres of red wine and it taste really good. I now want to make 23 litres, how much ingredients would I need to make this? Also, how much of the grape juice would I need to add to my 23 litre bottle, throughout the different stages

Barafundle on March 15, 2017:

Thanks for that, Dave, useful info. I've read a lot of your articles here and have learned a lot from them. I take your point re plastic but, when I started winemaking I put the word about a bit and I'm now up to my arse in free demi-johns!! Oh well.....such is life. Back to the VWP!

Dave McClure (author) from Worcester, UK on March 15, 2017:

Hi Barafundle - you only have 5 years on me! I worry less about sterilisation nowadays than I used to. In the old days of glass demijohns, cork or rubber bungs, fermentation traps, rubber tubing, you really had to be careful. Now, I ferment in new 5-litre plastic drinking water vessels and bottle in new 50cl plastic drinking water bottles. Always start a brew with an active yeast starter to ensure a quick start. The loosely fitted screw cap is all the fermentation trap you need. Check out my "How to Make Wine from Grape Juice" for my preferred method.

Now, to answer your question - How long a sterilising solution will keep depends on its strength and how you keep it so any answer is +/- 50% at least. But I wouldn't exceed two months or three uses, whichever comes first. Hope that helps!

Roger Phillips Barafundle from Tenby, Wales on March 14, 2017:

Hi Dave. I've just started winemaking (better late than never as I'm 70) and have a couple of queries concerning sterilisation of equipment. I've made up a VWP solution in a demi-john (for the large fermentors) and a litre bottle (for wine bottles).

Firstly, how long will it remain effective now it's been made liquid and, secondly, how many times could it be used before chucking out and replenishing?

ana on March 10, 2014:

just wanted to ask can u give a procedure on how to make a passion fruit wine thanks and god blesss

Dave McClure (author) from Worcester, UK on May 19, 2013:

Start the yeast in about half a litre of red grape juice. When fermenting well, defrost the berries to room temperature and crush them. Pour your fermenting yeast starter over the pulp. Let this ferment for about three days. strain the fermenting must off the pulp, pressing lightly. Don't try to extract every last drop. Then proceed as per my juice wine method, using around 500g sugar in a 5l batch, making up the bulk with red grape juice. You'll get plenty of blueberry flavour this way, and a better wine than 'pure' blueberry. I've missed out lots of detail, but there's enough to get you started. Good luck.

thor on May 18, 2013:

hi paraglider, i started making wine from supermarket fruit juices based on your process. I found it very simple and successful specially for a beginner like me!

I now want to make a blueberry wine from frozen blueberries I bought from a supermarket. Do you have experience to do this?

Can you teach me please? I love blueberries and I'm sure I would like the wine as well...

Dave McClure (author) from Worcester, UK on December 24, 2012:

Hi Jason - no danger at all if you use fruit juices in a balanced must as explained above. If you ferment grain or vegetables you have to be more careful, but even then, the methanol conent is very low and can only become dangerous if you concentrate it by distilling (which is not a part of the winemaking process).

Jason on December 21, 2012:

Is there any danger of the wine containing methanol? It's my understanding that when distilling grain alcohol, the first quart or so is methanol and poisonous... How does the natural fermentation process of wine compare?

Dave McClure (author) from Worcester, UK on January 22, 2012:

Wait until the bubbling stops, or slows down to almost nothing. Then put it in the fridge for a few days to help it fall clear. I can't tell you if it will be any good or not because 'a lot of sugar' could mean anything. Good luck with it, but if you're going to take up wine making, you really need to measure your quantities.

moufo on January 22, 2012:

I got about 20 oranges from my grandfathers tree in Alabama I pealed them an squeezed them add water a lot of sugar and a whole pack of yeast over bout 6 days I have it in a big hawian juice jug when I smell it its so strong smelling the smell bits u but it's a good smell I know I'm near the end but I have questions can it sit to long is another week ok an really what do I do to prepare it to be drinkable

Dave McClure (author) from Worcester, UK on October 13, 2011:

Thanks Klanguedoc - it's a great hobby and one of the few that can actually save you some money.

klanguedoc on October 13, 2011:

Thanks for the hub. I am very interested in making my own wine and beer and there is some to learn. Also, your page layout is fabulous.

Dave McClure (author) from Worcester, UK on October 12, 2011:

randy k - some yeasts fall clear better than others. Champagne yeast is good in that respect. There are many different fining agents, but some are suited to particular hazes and can make things worse if you use the wrong one. A good natural method is to boil a sliced banana in a little water and add the liquor (but not the pulp) to the must before fermenting. This usually results in a clear wine.

randy k. on October 12, 2011:

Great post. I've made several batches and I'm getting better wine with each successive batch. Clearing, or "fining" my wine is a problem. I've read that gelatin can be used for dining but I'm still having trouble getting my wines to totally clear. Is there a certain type of yeast or process that might help?

di kharel on September 15, 2011:

i want to lern practicaly how to make wine.i tried to find in glasgow but i can't.if any one halp to find for me any collage or factry in my nerest in glasgow area i will be pleaser.thank you

Dave McClure (author) from Worcester, UK on August 20, 2011:

klanguedoc - In Italy, vines grow almost like weeds and every other cottage has access to fresh wine grapes. And of course with so much wine-making going on, the natural wine yeasts are everywhere (that's what the 'bloom' on red grapes is made of). In Northern climes, like UK, or in the Arabian desert where I now live, there are no such natural advantages so you have to apply some science! I bet your father-in-law's wine in perfect!

klanguedoc on August 19, 2011:

I have been making wine with my Father-in-Law for the last couple of years. He is Italian and he makes it as they did for hundreds of years. You filled in a lot of missing pieces about the process.

Dave McClure (author) from Worcester, UK on February 25, 2011:

most welcome :)

funky23 from Deutschland on February 24, 2011:

well done post thank you for the tips :-)

Dave McClure (author) from Worcester, UK on November 09, 2009:

Greetings - Let me know when it's ready and I'll come to the party :)

prettydarkhorse from US on November 09, 2009:

ok, I will try it and will tell you what happen LOL, thanks, good day to you, maita

Dave McClure (author) from Worcester, UK on November 08, 2009:

Maita - just give it a go, but make sure the juice is free of preservatives and use a proper wine yeast. Good luck :)

prettydarkhorse from US on November 08, 2009:

Hi dave! I am reading through this and I am learning a lot from this one, I understand some basic concepts like the yeast (important), fermentation (specially the juice) etc.

Now I feel like I am going to try it but still If I am not fully confident that I can do it and be patient with it, but I will get all your notes about winemaking and it is a good start for me...

Thanks for the information here, well written and easy to understand..

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