Even with care, the use of correct procedures and attention to detail, faults sometimes still develop. Here are the most common faults and remedies. 


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: 

  • The must contains too much sugar and the yeast has been inhibited. Remedy: Dilute with water until the S.G. is below 1.100 (approximately 23/4 lb sugar per gallon or 1.25 kg per 4.5 litres). 

  • Insufficient acid. Taste the must, and if lacking in acid, add 2 teaspoonfuls of citric acid per gallon (4.5 litres) or adjust to pH 3.3. 

  • Too much acid. Unlikely, but if the pH is less than 3.0, the yeast may have been killed or inhibited. Remedy: Dilute the must to reduce the acidity. Alternatively, neutralize the acid by adding potassium carbonate solution. Method: Dissolve 2 oz potassium carbonate in 1/4 pint of water (60 g in 150 ml) and add to must a little at a time, stirring well and tasting after each addition until the acidity is correct. Note: 3 teaspoons of this solution will reduce the acidity of 1 gallon (4.5 litres) by about 1 ppt. 

  • Insufficient nutrient. Remedy: Add the recommended dose of a good brand of nutrient together with two vitamin B, tablets per gallon (4.5 litres). 

  • Must is too cold. Remedy: Move it into a temperature of 20 - 25 degrees C (68 - 77 F). 

  • Must is too hot. The yeast will be destroyed if it is added to a must at a temperature of over 30 degrees C (86 F). Remedy: Prepare a new yeast starter and add it to the cool must. 

  • Yeast inactive. If any sulfite is added to a must, the yeast must be introduced 24 hours later or it will be killed. Remedy: Make up a fresh starter and add it to the must. 


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. 


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. 


Remedy: Reduce acidity of a finished wine by using a "Wine Acid Reduction Solution" or potassium carbonate solution as described in 3 above. 


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. 

  • Mousey flavor. Anyone who has experience of mice will know what this means! In fact the wine initially tastes sound, but leaves a very unpleasant after-taste on swallowing. Oddly, some people cannot detect this. Certainly caused by bacterial infection. Remedy: There is none. Throw the wine away and sterilize the equipment used. 

  • Medicinal flavor. And it really does taste just like some medicines! Caused by a lack of acid in the must. Remedy: There is none. Throw the wine away and include more acid in the next must. 

  • Bad-egg smell. May be caused by adding yeast to a sulphited must too soon. Remedy: Try adding one Campden tablet per gallon (4.5 litres). If this has no effect, throw the wine away.

  • Geranium smell. Caused by using sorbate stabilizer without a Campden tablet. Follow the instructions on all such preparations. Remedy: There is none. Throw the wine away.

  • Acetification or vinegar formation. Self-explanatory. Caused by bacterial infection. Remedy: There is none. Pour the wine away. Note: Beginners sometimes confuse the bouquet of a bone-dry wine (especially apple) with the smell of acetic acid. Be sure that the wine is acetified by sweetening slightly and then tasting it. 

  • Other off-flavors. These can be hard to identify. Caused by plastic or metallic equipment, detergents, an excessive amount of yeast nutrient, bacterial infection, leaving the wine in contact with dead yeast sediment or finings sediment, and so on. Such wine may be used for cooking, but is best thrown away. 


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. 


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. 


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. 


Probably the result of too little tannin and/or acid. Remedy: Add a little extra tannin to taste. 


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).


There are several causes, the main ones being: 

  • Yeast in suspension. Remedy: Move the wine to a cooler place and add the recommended amount of a stabilizer such as potassium sorbate.
  • Pectin haze. Test for pectin haze by adding four parts of methylated spirit to one part of wine, mixing and leaving for thirty minutes. The formation of clots, strings or jelly indicates pectin in the wine. Remedy: Add a liquid pectic enzyme, 1/2 fl oz per gallon (40 ml, per 4.5 litres) and leave until clear. Siphon off the sediment if necessary. Starch haze. Test by adding a drop of brown iodine solution to a small volume of wine. A blue-black coloration indicates starch. Remedy: Add fungal amylase or diastase and leave until clear. 
  • Lactic acid bacteria infection. This produces a thick, slimy or oily appearance. Remedy: Add two Campden tablets per gallon (4.5 litres), vigorously beat the wine with a spoon in a bucket and filter. 5. Other hazes. May be fined with bentonite. But if the wine has an odd color or metallic flavor, throw it away. 


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.

Next: winemaking with concentrated grape juice



Original posting date
01 January 2018