It’ll be all bright on the night
by Ray Alton
It is apparent that todays’ drinker drinks with his eyes. Whilst a tight head on a pint may be an optional extra dependent upon where the beer is being sold, the requirement for optimum clarity is universal. Cask conditioned beers are – unfairly perhaps – compared to lagers, keg and small pack products, and need to stand the comparison well.
To assist the brewer three types of finings are used. Copper finings, Isinglass finings and auxiliary finings.
These are produced from the swim bladders of tropical and sub tropical fish – Historically the sturgeon, nowadays various species of threadfin, a sub-order of the sturgeon family are used. The bladders are part processed into ‘fish maws’ before being cut or soaked in a blend of fruit acids in dilute aqueous solution. The acids used are typically malic, tartaric, citric and sulphurous acids. This cutting process does not dissolve the fish maws, but rather allows them to soak up water to form a colloidal solution.
A colloidal solution acts much like a true solution in many respects, but does have some distinct properties: It consists of two distinct phases, a liquid and a solid phase in a stable emulsion.
The stability is pH dependent. As supplied, at pH 2·5 or thereabouts, the colloidal system is stable. As the ‘Iso Electric Point’ is approached – about pH 5·5 (dependant upon Isinglass composition) – the colloid becomes intrinsically unstable and the solid phase starts to precipitate out of the liquid phase. This is fundamental to the way Isinglass finings work.
The active ingredient in isinglass is a protein called collagen, a triple helical coil with many sites of positive charge. It is a large molecule, with a molecular weight in the order of 350,000. On the other hand yeast cells are very small – a beer at rack usually contains in excess of one million yeast cells per millilitre of beer, whilst during fermentation 40 million cells per ml. is typical. Even bright, fined beer contains about 104 yeast cells per ml. (10,000 per ml).
Generally speaking top fermenting brewing yeasts have a negative electrical charge. As then with magnetism opposites attract, and the negatively charged yeast cells are attracted to the positively charged collagen molecules. This does not occur on a ‘one to one’ basis however. Many yeast cells are attracted to each collagen molecule because of the enormous difference in size and charge, becoming physically enmeshed within the collagen molecular structure. A floc is thus formed and aided by the instability of the colloidal system caused by the beer pH and gravitational forces the collagen precipitates from the beer taking enmeshed yeast cells with it and clarifying the beer.
Types Of Finings
There are a number of different types of Auxiliary Finings, the most common being based on acidified silicates such as Finings Adjunct. Polysaccharides (Gums such as Acacia, Gum Arabic) and seaweed extracts – finings based on carrageenans or alginates are also used. Blends of part silicate/part polysaccharide finings also form a major part of the finings used, as typified by the Cellabrite range.
All of these systems are colloidal solutions. They carry a high negative charge and react with positively charged proteins, including collagen, to form flocs. The proximity of the Iso Electric Point of the colloidal system combined with gravitational forces cause the flocs to precipitate from the beer taking the enmeshed proteins with them. The theory then is identical to that of the Isinglass/yeast floc except that the charges are reversed.
The choice of Auxiliary will vary dependent upon the individual beer. The spectrum of proteins present will usually react positively to a number of different finings agents, but just occasionally one finds a beer that will respond to only one particular type.
There are many advantages gained by the judicious use of an Auxiliary fining agent, and these include:
• Reduced use of Isinglass Finings
• A better polish on the finished beer
• Increased speed of fining
• Increased speed of re-settling
Silicated finings also give:
• Stabilisation against non-biological haze formation
• A degree of protection against chill hazes
Fined beer still contains many proteins of small molecular size and weight, and they are not visible. During the shelf life of the beer these proteins will undergo chemical changes, and will increase in size until they eventually become visible and we have a protein haze. However silicated auxiliaries, large densely negatively charged particles, do not need to ‘see’ the protein in order to form a floc. It needs only to have a sufficient electrical charge for electro-chemical attraction to occur for that protein to be removed. The use of silicated auxiliaries then produces a final beer with a lower concentration of proteins, and those proteins are of a lower spectrum of size. During the shelf life of the beer these proteins, from the smaller start, will take longer to grow to a size at which they are visible, and the beer therefore has an increased shelf life against non-biological haze formation.
Similarly chill hazes are caused by proteins that are soluble – and therefore non visible – at normal beer temperatures, but which are insoluble and precipitate from the beer at colder temperatures. By the mechanism described above some of these proteins are precipitated by a silicated auxiliary during conditioning, and the beers overall propensity to form a chill haze is reduced.
The use of the correct balance of Isinglass and Auxiliary finings will rapidly clarify a beer containing:
• 0·5 – 2 x 106 viable yeast cells per ml.
• 1 – 3 x 106 non biological particles (mainly proteins) per ml.
Finings systems will not adequately remove:
• Colloidal hazes caused by metallic contamination
• Bacterial infections
• Dead yeast cells
• Wild yeasts
• Beers with particle loadings much higher or lower than the optimum
You will see again then how correct choice of plant and materials, mashing and sparging regimes, hygiene standards and yeast handling keep cropping up again and again.
There are three principle objectives of beer fining:
• Bright beer
• Rapid speed of fining
• Tight and minimal cask bottoms
The emphasis that any particular brewer will place on these objectives will determine his assessment of the best type of auxiliary and the optimum usage rate.
The Speed of Fining:
The rate of fining is governed by gravitational forces as stated in Stoke’s Law, which highlights the criteria which are important for the optimisation of a finings system:
V = the velocity of precipitation
d = the floc diameter
S = the floc density
S1 = the beer density
g = gravitational constant
µ = the beer viscosity coefficient
It can be seen then that the speed of fining is directly proportional to the square of the particle diameter. Therefore if we increase the floc diameter by a factor of 10, we increase the fining rate by a factor of 100.
The density of the floc will also affect the speed of fining, the more dense the faster the fine. This explains why larger collagen molecules fine faster than small ones , since the larger the molecule, the more sites of positive charge it will have, the more yeast cells it will attract and enmesh and the larger and denser the floc will become. The same principle explains why the very large silicate molecules fine faster than alternatives.
The density of the beer is practically a constant of value 1, since variations between say ‘a thousand and six’ (1·006) and ‘a thousand and eight’ (1·008) are insignificant.
The gravitational constant, g, is indeed a constant to the Microbrewer. No problem to the national brewer, who will spend 60 – 70K on a centrifuge, pull 5000 g on the beer, and ‘fine’ it in 15 seconds rather than 24 hours!
The importance of beer viscosity can also be seen from Stoke’s Law. An increase in viscosity (attributable to ß-glucan or pentosans derived from poorly modified malt) causes a disproportionate decrease in the fining rate because of the factor of 18 by which it is multiplied.
The depth of the vessel is taken as ‘Unit Depth’, and in trade the deeper the fining vessel or tank the longer the fine will take.
Use of Finings:
There is a good deal of latitude in the point of use of finings. As a general rule of thumb the Auxiliary should be added first, preferably 24 hours or so before the addition of the Isinglass. Where the Auxiliary is added will depend upon the plant in use. If a Racking Tank is available, the Auxiliary should be added to this tank as it is being run up. If the casks are filled direct from F.V., the Auxiliary should be added direct to the Fermenter after the yeast crop has been skimmed and the coolers put on. Only gentle agitation is required, and it is essential to have a stand pipe or thimble in the vessels in order to retain the flocs in the F.V.
Isinglass finings should always be diluted to Ready for Use (RFU) strength prior to use. A case can be argued for this dilution to be carried out with cold water or with beer. My preference is for water, because the vigorous mixing required causes aeration, and introducing oxygen to the beer post fermentation can cause off flavours and instability. If a brewer does use beer to mix the finings, they must be then immediately added to the cask to minimise the risk of picking up infections. Diluting the isinglass with water then has distinct advantages. Sufficient RFU isinglass for about one weeks use can be made up at a time, and this can be prepared a day before the first intended use in order to allow time for any air introduced to the finings to dissipate.
Isinglass finings should then be added to the beer at rack or despatch. Since in the case of small breweries there is little difference between the two, and to broach and reseal the casks is a potential source of introducing infection, we would recommend adding the isinglass to the casks at rack and mixing well.
These should be carried out on a regular basis, and certainly when a new seasons malt comes on stream. Usage rates need to be optimised both to ensure economic cost is achieved and in order to gain the best possible results. Over fining can cause hazes just as under fining can leave hazes: It is not a case of 1 pint best, 2 pints better. An ideal way to check your beer fining performance is by using milk bottles. Using the ratio of:
1 ml º 1 pint,
568 mls º 576 pints º 2 barrels
we can add finings to the beer, 2 mls per bottle being equivalent to a pint per barrel addition in trade.
An optimisation is run by making trials to optimise the rate of Isinglass addition within the range of 2 – 5 pints per barrel by adding 4, 6, 8 and 10 mls of RFU Isinglass to 4 labelled milk bottles and mixing well.
Samples containing Auxiliary finings within the range ½, 1, 1½ and 2 pints per barrel are set up to run concurrently.
After an appropriate time interval, which will vary with beer type, an assessment is made of the optimum rate of isinglass required to fine the beer. This will not necessarily be the brightest beer, since the Auxiliary will improve the polish. With the Isinglass we are looking for the point at which an extra pint of Isinglass appears to add only excess bottoms, with no appreciable improvement in clarity. This rate of Isinglass is then added to all the sample bottles of Auxiliary finings, mixing well. It is then quite easy to check the effects of 3 or 4 re-settles as required.
Once an optimum rate has been assessed, it is important to keep a check to ensure that it is going to work. Take a sample of the beer, either from FV after fermentation or from the Conditioning Tank/Racking Back. Add to this the equivalent rate of Auxiliary and mix well. An hour or so later add the optimum rate of Isinglass and remix. Within a short period of time you should see floc formation and clarification of the beer occurring. You can then have peace of mind that the beer should fine well in trade.
However the real purpose of this verification is to find the one occasion when the beer doesn’t fine. If you do not get a satisfactory result in a milk bottle then you are highly likely to experience a problem in trade. This simple procedure means that you have an early warning of a potential problem, and that you can take the necessary corrective action whilst the beer is still in one tank and under your full control. Addition of an extra pint per barrel of auxiliary for example is rather easier in a 10 barrel tank in the brewery than it is in 40 firkins spread far and wide in the trade.
The fining of a beer and the propensity of a beer to form hazes is dependent upon many factors:
1. Liquor Composition
An adequate calcium level to precipitate phosphates, proteins and oxalates
Control of mash pH
Absence of heavy metals, colloidal silica, etc.
2. Malt Quality
Well modified malt is required, with reduced ß-glucan levels. High levels of ß-glucan leads to high wort and beer viscosities
3. Mash pH and temperature
Governed in part by liquor composition
Lower pH values optimiseproteolysis
4. Gravity of last runnings
Excess sparging will leach undesirables from the mash, leading to subsequent haze forming potential and fining difficulties. Exacerbated by high pH values, when extraction of tannins and silicates is optimised.
5. Length and vigour of the boil
Adequate boiling ensures sterility and promotes protein precipitation.
The effectiveness of the copper finings regime is fundamental to final beer clarity and fineability, and is dependant upon pH.
6. The removal of trub
Excess trub (Nitrogenous compounds) allowed through to the FV can cause problems by:
• coating the yeast, leading to poor fermentations.
• Much reduced final beer stability.
• Finings difficulties.
7. The yeast strain/s used
Yeasts may be very flocculent or powdery, or anywhere between the two extremes. In practise most breweries use a yeast that contains a mixture of strains, the flocculent yeast rapidly settling out to improve fining performance whilst the powdery yeast remains in the beer to provide those last few degrees of attenuation and conditioning.
• Yeast count at rack.
• Top or bottom fermenting yeasts.
• Adequate Calcium levels to promote flocculation.
Vessel used – FV, CT, Cask.
Time and temperature – the colder the conditioning temperature the more likely we are to remove potential chill haze forming proteins.
The attenuation limit of the beer – how many degrees of fermentability are left when you crop the yeast and put the coolers on. 1 – 3 is about right for a cask conditioned ale. Above this the secondary fermentation process will be too vigorous increasing yeast count, producing excess carbon dioxide and causing turbulence within the beer that reduces fining performance.
Beer pH and viscosity.
9. Quality of the Finings system used
There are a number of different types of auxiliary finings available. One particular type may work better on your beer than another. Not all Isinglass finings are the same. Just as a brewer selects his malt or hop grist, so a manufacturer of Isinglass finings selects blends of raw material in order to meet his own quality and cost criteria.
It can be seen then that brewing is a fully integrated process, and that the actions taken at any particular stage have a direct effect on all subsequent stages. It is no use getting to the end of fermentation and then expecting a finings regime to produce a bright and sparkling pint if you have failed to observe good brewing practise throughout the process.