Even with care, the use of correct procedures and attention to detail, faults sometimes still develop. Here are the most common faults and remedies.
FERMENTATION WILL NOT START
Always allow at least twelve hours between the addition of yeast and the first active signs of fermentation. If it is clear that the must will not ferment, there are several possible reasons:
FERMENTATION STARTS BUT SOON STOPS
This usually happens because the yeast is weakened by excess sugar and can then tolerate only low levels of alcohol. Other causes include all those listed above. Remedy: Agitate the must by pouring it into a new container. Make up a fresh yeast starter and after it is established, add an equal quantity of must. Wait until fermentation is vigorous, then add same volume of must, and so on, until the whole is fermenting again.
WINE IS TOO SWEET
With low level of alcohol, indicates a "stuck ferment": see above. With high level of alcohol, suggests a complete fermentation up to the limit of the yeast's tolerance of alcohol. Remedy: Blend with a dry wine and use less sugar in the must next time.
WINE IS TOO ACID
Remedy: Reduce acidity of a finished wine by using a "Wine Acid Reduction Solution" or potassium carbonate solution as described in 3 above.
WINE HAS AN OFF-FLAVOUR OR UNPLEASANT SMELL
The main causes of unpleasant flavors and odours in wine are listed below. Don't confuse these faults with the yeasty smell and taste of a wine which has not cleared completely.
WINE SMELLS OR TASTES LIKE SHERRY
Result of acetaldehyde formation due to presence of air. Remedy: Try dissolving one or two Campden tablets in each gallon (4.5 litres). The problem can be avoided by ensuring that all storage containers are topped up.
WINE LACKS BOUQUET
Caused by a lack of acid in the must. The addition of 1 teaspoonful of lactic acid per gallon (4.5 litres) and further maturation may help.
WINE LACKS BODY
The body of a wine does not necessarily refer to its viscosity or thickness, but to the presence of enough fruit and an overall well balanced drink. A wine which is too "thin" and watery probably had too little fruit in the must. Remedy: Stir in a little concentrated grape juice. This will also sweeten the wine.
WINE TASTES FLAT OR INSIPID
Probably the result of too little tannin and/or acid. Remedy: Add a little extra tannin to taste.
WINE IS TOO ASTRINGENT OR BITTER
Astringency is the result of excess tannin. It is not the same as bitterness, which is much more likely to be a result of including sour or inappropriate ingredients such as citrus pith. Remedy: Excess tannin can be removed by fining with isinglass or longer maturation. Bitterness may be masked by adding up to 2 fl oz (60 ml) of glycerol per gallon (4.5 litres).
WINE WILL NOT CLEAR
There are several causes, the main ones being:
A wine which has been transferred to bottle or vessel begins to ferment once again. This can occur if the wine was not allowed to ferment to dryness, not racked correctly, or bottled while still fermenting. It also happens if sucrose is added to sweeten a wine which still contains some live yeast Clearly the production of carbon dioxide gas in bottle or a large glass vessel is inconvenient or even dangerous, with the risk of corks blowing out or burst bottles.
There are several possible remedies. If the wine is still in bottles, and you wish to keep it you could replace the corks or stoppers with a safety-valve. This is a neat plastic stopper that contains a ball valve which allows any carbon dioxide gas produced to escape. (Similar stoppers are available for demijohns.) A rubber bung and air-lock would serve the same purpose. Another alternative would be to pour a small amount of wine out of each bottle and replace it with a wineglassful of brandy or spirits.
This should increase the strength of the wine to the point the yeast stops working. But better solutions to this would be to pour the wine back into a demijohn or vessel and either: let fermentation proceed to completion or add a stabilizer such as potassium sorbate. This is a very powerful inhibitor of mould and yeast growth; the recommended rate of use is 1 gram per gallon (4.5 litres). Don't use it with a Campden tablet or a geranium smell may develop.
Sorbate will remove all yeast cells and leave a stable wine. By the way, don't try to stabilize a wine that is still fermenting by adding Campden tablets alone. The amount needed to kill a good wine yeast is about eight tablets - a level which would certainly spoil the wine, and might even be a health hazard. The correct use of Campden tablets is to use one or two tablets in a finished wine to protect the wine from oxidation and bacterial infection.
Original posting date
01 January 2018