Fining and Filtering Home Made Wines

If a must is correctly prepared, the wine should clear quickly of its own accord after fermentation. But sometimes a wine stubbornly refuses to clear - even after many months in storage. It may then be "fined". The use of wine finings precipitates out any suspended solids and leaves a clear wine. The only two types which need concern the modern winemaker are isinglass, a protein substance, and bentonite, a powdered clay.

Isinglass is a thick, liquid, proteinaceous substance which is stirred into a little of the wine and then stirred into the bulk. Full instructions will be provided when the substance is purchased - it is available under various brand names such as Wine fine and Wine finings - but the usual amount is 0.5 oz (15 g) per gallon (4.5 litres). 

The protein molecules coagulate with the particles causing a haze and drag them to the bottom of the container, where the whole mass forms a thick sediment. This is a fairly rapid procedure, taking from six hours up to two weeks - the exact time depends on the chemical composition of the wine. The trouble with isinglass is that it also reacts with the tannin and other elements of the wine itself: too much isinglass will therefore remove body, color, bite and bouquet from the wine. This is called "over-fining", and it is a very real danger.

In addition, some hazes are quite unaffected by - the substance. Whenever isinglass has been used to fine a wine, more tannin should be added to taste afterwards to replace that which has been precipitated out by the isinglass. 

Bentonite is also an effective fining agent and it has the added advantage that it cannot over-fine a wine. It Is usually sold as a sterile, dry powder which must be mixed with water and allowed to form a gel before being mixed into the wine, although sachets of ready prepared gel can now be purchased. Bentonite clears some hazes that isinglass will not touch; but there is no cure for pectin or starch hazes except the appropriate enzyme. 

Whether you use isinglass or bentonite, once the wine has cleared and a thick sediment of finings and suspended material has precipitated out, rack the wine into a clean, sterile container.


Filtering is the last resort for clearing a wine. It cannot remove or starch hazes from a wine, and what it can achieve (the rapid removal of microscopic particles from a wine) would perhaps occur in time anyway. 

One situation where filtration may be genuinely useful is when a wine has been prepared for drinking soon after fermentation has ended and the yeast needs to be removed at once. Another use is to "polish" an already clear or bright wine when 100 per cent crystal clarity is required - on special occasions, or when exhibiting, for example.

There is an indefinable loss of quality on filtering, so It is to be avoided if possible. However, if you decide it is necessary, say because a wine simply will not clear, then you have a choice of two methods open to you. 

The first involves beating a powder into the wine and then passing it through a filter bag. The powder gradually forms a layer on the inner surface of the bag and prevents any particles in the wine passing through. This type of filter is only acceptable if the bag and wine are enclosed in some kind of container which excludes the air. 

The second method is to use a filter kit which siphons the wine through a fine filter pad or layer of filter powders built up on a porous plastic sheet. The wine is not exposed to the air and can be left to trickle through gradually. There is little to choose between the different systems available, although for sheer speed, it is hard to beat those which have a pump pressurized container to force the wine through the filter. Incidentally, it is hopeless trying to filter wine through a filter paper in a funnel. The fine grade necessary for effective filtration is impossibly slow. 

To sum up: as a general rule, fining and filtering are to be avoided. Fining interferes with the chemical composition of a wine, filtration removes some of the quality. Patience and time are much better and often just as effective agents for clearing a wine! 


All wines benefit from a period of storage in demijohn before they are bottled. The necessary chemical changes which take place before a wine is mature can occur better in bulk. If you cannot keep the wine in demijohn for the period recommended in the recipes, bottle it after the second racking. 


The first step in calculating the alcoholic strength of a finished wine is to subtract the final S.G. of the wine from the initial S.G. of the must after all the sugar has been added and the liquid made up to its full volume. 

Example: Initial S.G. 1110 (omit the decimal point); Final S.G. 995; Drop in gravity 115

Next, the figure obtained in this way is divided by 7.4. The result obtained is the % alcohol by volume in the wine, i.e. 115 / 7.4 = 15.5% alcohol. Although this method is unlikely to be accurate to within 0.5%, it Is a good approximation. 

Problems arise, of course, if you have added the sugar in stages, because the volume of the wine changes after each addition. The % alcohol can then only be calculated by determining the sum of all the drops in gravity between the various additions of sugar and adjusting for the changes in the volume of the wine. However, this is a tedious and inaccurate procedure. In such a case it is much more realistic simply to add up the total weight of sugar added to the wine and use the hydrometer table to determine the potential % of alcohol. 

This should correspond to the % alcohol in the finished wine - provided that it is dry, i.e. that all the sugar has been fermented to alcohol. If the fermentation was stopped while the wine was still sweet, or if sugar has been added before the final S.G. was determined, the following method is the one to use. 


This method relies on the fact that alcohol evaporates at a temperature well below the boiling point of water. So when a wine is heated, the alcohol evaporates, and as it does so, the S.G. of the wine increases. This method has the advantage that one does not need to know the initial S.G. of the must.


1 The wine's final S.G. is measured. 

2 A sample of wine is then transferred to a bottle of about a half pint (300 ml) capacity - the volume is not critical - and the level of wine is adjusted exactly to a mark on the narrowest part of the neck. 

3 The wine is then poured into a pan (or preferably a flask) and boiled for five minutes so that the alcohol is driven off . The loss of spray droplets should be minimized, so boil gently.

4 The liquid is then allowed to cool, transferred back to the measuring bottle and topped up with water exactly to the measurement mark, so that its volume before and after boiling is the same - but without the alcohol.

5 The S.G. is measured once again. The first reading is subtracted from the second and the alcohol level obtained by reference to the table below.

S.G. after boiling 1.019
S.G. before boiling 1.003
Increase in S.G. 0.016

Refer to table:
0.016 = 12.3% alcohol.

Note: Although the actual temperature at which the S.G. is measured is not critical, the first and second readings of the S.G. must be taken at the same temperature.

Calculation of Strength of Wine from Increase in S.G. on Boiling

Increase in S.G.

 % alcohol by volume



Although the accepted modern method of expressing the alcoholic content of drinks is the % alcohol by volume, one often still sees references to degrees proof. The conversion between these two systems is simple:

To convert from % alcohol to degrees proof

Multiply by 7, divide by 4
Example: 15% alcohol = (15 x 7) / 4 = 26.25 degrees proof

To convert from degrees proof to % alcohol

Multiply by 4, divide by 7
Example: 70 degrees proof = (70 X 4) / 7 = 40% alcohol

Standard spirits - whisky, vodka and so on - are 70 degrees proof, or 40% alcohol by volume.


Unless you are experienced, it is difficult to judge accurately the alcoholic strength of a finished wine. Don't, therefore, assume that your wine is weak without first tasting a commercial wine of similar type. However, if your wine is low in alcohol, or if you wish to use the wine as a dessert wine or as "port" or "sherry", you may want to add either a stronger wine or a spirit to increase its strength. Vodka is ideal for this purpose, of course, since it has no flavor of its own; alternatively, "Polish Spirit", which is twice as strong as vodka, can be used. A word of warning, here, though! The alcohol in beers, wines, spirits and so on is ethanol (also known as ethyl alcohol). All other alcohols are very poisonous. You MUST therefore use a reputable supplier or brand of spirits.

The calculation of how much spirit need be added to a wine to increase its strength by a known amount can be simplified by use of the Pearson Square, which looks like this:

A   D
B   E

where A = Strength of spirit to be added, B = Strength of wine at present, C = Required strength of wine after fortification, D = C minus B, and E = A minus C 

The proportion of spirit to wine which will give the desired result will then be equal to D/E (D divided by E).

Example: 4.5 litres of wine at 13.2% alcohol by volume are to be fortified to an alcoholic strength of 17% with the use of 70 degrees vodka. How much is needed?


Convert all strengths to same units, here, degrees proof:

13.2% alcohol = 23X 17% alcohol = 29.75

Substitute these values as follows:

A Strength of spirit to be added = 70
B Strength of wine at present = 23. 1
C Strength of wine required = 29.75
D =  C - B  =  29.75 - 23.1 = 6.65
E  = A - C   = 70 - 29.75 = 40.25

The required proportions of spirit and wine are D:E, in other words, 6.65:40.25 = 1:6 (approximately). Therefore 4.5 litres of wine would require the addition of one-sixth of that volume of spirit, i.e. 750 ml.

Next: blending wines



Original posting date
01 January 2018