Equipment and procedures

From left to right: dark 1 gallon demijohn, empty 1 gallon (colourless) demijohn, hydrometer and jar, hydrometer and thermometer

Use of the equipment

In the recipe section you will see references to demijohns. These are nothing more than 1 gallon jars. The dark ones are best for red wine - this avoids damaging light intrusion which can decolourise your wine and even give it off flavours. Don't worry if you can't get hold of brown glass demijohns - wrapping an ordinary one in aluminium foil works just as well! The demijohns are fitted with a bung into which an airlock is placed. This is a simple device which allows carbon dioxide gas to exit the fermenting wine. Because the airlock is filled with water, air and oxygen cannot make the return journey since the demijohn is under positive pressure during the fermentation process.

You will also see a hydrometer. This is a simple weighted glass device which floats in the liquid. The higher the specific gravity (a measure of density) the higher the hydrometer floats. It is graduated so the actual specific gravity can be read off the scale. As this reading is temperature sensitive, it is best to make this measurement at 20 degrees celsius (the temperature at which most S.G. tables are quoted).

At the very beginning of a fermentation, the S.G. is high because the must (winemakers talk for fruit juice!) is high in sugar. Alcohol and water mixtures have a lower S.G. than sugar and water - so the S.G. falls as the fermentation proceeds. Sometimes a recipe will tell you to move on to the next stage when a certain S.G. value has been reached. You can see how useful the hydrometer is to tell you how the wine is progressing!

From left to right: a very young wine! It looks so disgusting one might be tempted to ask "is it worth making this stuff?". Middle picture: like the one on the left after a few weeks. All the yeast has settled to the bottom. Right hand picture: after racking off the deposited yeast. The clear liquid certainly looks more palatable now!

Winemaking involves some simple steps. In general these amount to:

extracting the juice of certain fruits (for REAL wine this has to be grape)

adding water and sugar (the more sugar - the more alcohol - up to a point!)

adding yeast (to begin the fermentation)

Allowing it to settle, then racking off (winemakers talk for siphoning the clear liquid off the settled yeast)

Racking again, then bottling.

Initially, the fermentation is begun in an open bucket. The yeast begins to grow if oxygen is present. This is the aerobic phase of yeast reproduction. During this aerobic phase, the yeast will grow, carbon dioxide gas will be generated, but not much alcohol will be produced. After a week or so of "fermentation on the pulp" the pleasant fruity flavours are extracted into the must. The wine is then transferred to a demijohn - and the oxygen supply is shut off with an airlock. This is crucial: it causes the yeast to switch to a less efficient anaerobic form of respiration. Now, alcohol is produced. Another good reason to employ an airlock is that it gives a pretty good indication when the fermentation is over since the number of bubbles produced falls to an imperceptible minimum. It is worth stating that fermentation only allows up to 18% alcohol production. The reason is that as alcohol builds up in the vessel, it begins to poison the yeast. In effect, it renders it useless. Table wine is generally about 12 - 13% alcohol. Some yeasts can tolerate the higher levels of 18% but you need to get these from a specialist winemaking supplier.

In fact, you should only use proper wine yeast for all fermentations - unless you want off flavours in your wine!

In order to get wine of quite high alcohol level, it is important not to add all the sugar at once. Rather the wine is "fed" the sugar at intervals as the fermentation proceeds. This allows the yeast to become aclimatised to the conditions - it stops the organisms being overwhelmed by (to them) toxic ingredients.

Now a word about cleanliness: since the process involves microorganisms (yeast) we want to ensure we only have these present - and no bacteria or wild yeasts! For this reason it is essential that you sterilise all equipment by washing it in a weak solution of sodium metabisulfite. You can buy this at all good winemaking stores. Generally, about a level teapoonful in a pint of water will be OK. The solution releases sulfur dioxide which kills bacteria and unwanted - so called - wild yeasts. Sometimes, the fruit itelf is sterilised with this material. It doesn't matter if a little is left on the fruit - your wine yeast should be able to cope, provided it's only a small quantity. Sometimes a recipe calls for boiling water to be added. This, of course, also sterilises the fruit. A word about the consequences of poor hygiene and sloppy practice: your wine could easily develop off-taints. Have a look at this link to see what can happen:

http://en.wikipedia.org/wiki/Wine_fault

A word about Campden tablets. These are just a compressed form of sodium metabisulfite. Some have a little starch added as a binder. All Campden tablets are useful if you want to add a small measure of sodium metabisulfite to your wine. Sometimes this is done deliberately to ensure fermentation has well and truly stopped prior to bottling. It helps prevent burst bottles if the bottling is done too enthusiastically! Also, since sulfur dioxide is a reducing agent, it can help prevent oxidised flavours occuring in your wine. Be careful not to overdo the Campden tablets though - it is possible to get quite nasty sulfur compounds generated - which smell truly awful!

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Anne Gille | Reply 12.10.2014 16.34

Cleared up many questions I had about grape wine making. But I still don't know about airlocks. Does one have to release the gas every so often or leave alone??

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