The Use of Irish Moss as Copper Finings


The following paper was read and discussed:

by Clerk Ranken, D.Sc.

Irish Moss (Cliondrus crispus) or Carragheen has long been in use in the brewing industry as copper linings.  At one time its use could be regarded as a “secret remedy”, but during the last sixteen years, and probably earlier, numerous references have been made to it in the brewing journals.  H. T. Brown (this Journ,, 1913, 84) in one of his papers on ” The Nitrogen Question,” mentions it as a means of improving the flocculation of the wort, whilst Ling {ibid., 1915, 512) discusses its possible influence on the fermentation owing to the removal of peptone from the wort by its agency.

The moss grows well down on the rocks and can only be gathered or dredged by long rakes at very low spring tides.  When freshly gathered, it has a dark purple to black colour, and is dried and bleached by being spread out on the fields where it lies exposed to the action of the air and the sunlight.  The composition of the moss is not simple.  From work done in this connection by Haas, B. Russell-Wells and others (this Journ., 1927, 402), it appears to consist essentially of two components, one of which is very soluble in cold water, and the other slightly soluble in cold water, but quite soluble in hot water.  The cold water extract produces a thick viscous solution, whilst the portion soluble in hot water gives a solution which tends to gelatinise on cooling.  In addition, there is always a percentage of the moss which is insoluble in water and remains as a gelatinous skeleton, consisting chiefly of cellulose.  The constituents soluble in cold and in hot water are composed of carbohydrate complexes united to calcium and sulphate, with traces of magnesium, sodium, iron, etc., and can be looked upon as ethereal sulphates.  The viscosity of a mucilage made from the moss grows less on keeping, eventually reaching an approximately constant value.  The same result is brought about by boiling and by the addition of certain acids.  This latter point is of some importance, and will be referred to later.  As bought by the brewer, the moss contains on an average approximately 17 per cent, of moisture.

Its excessive solubility in cold water is apt to be overlooked owing to the swelling up of the moss by the imbibition of the water.  Even, if the moss is merely covered with water and allowed to stand for ten minutes and stirred once, the amount entering solution amounts to over 17 per cent.  With more water, a more prolonged steeping or with more frequent stirring, the amount dissolving can rapidly be increased.  This is a point of some importance and has to be considered when weighed quantities of the moss are being prepared for use in the copper, owing to the custom of subjecting the moss after weighing to some method of washing before adding the gelatinous residue to the boiling wort. If this is done the actual amount of moss added to the wort becomes more or less a variable quantity depending on the method of treatment, which may very easily vary from day to day.  The only exact method of adding the calculated amount is to avoid washing the moss and add it in the dry condition to the copper.  Any small amount of extraneous matter can be got rid off by teasing out the moss, followed by vigorous shaking.  There is, of course, nearly always a small amount of adhering inorganic matter, but, as this consists chiefly of calcium carbonate with traces of iron, it should do no harm, unless, as is unlikely, it is present in sufficient quantity to counteract the acidity of the wort and lower the hydrogen-ion concentration.

When the problem of the action of Irish moss on boiling wort is examined, it resolves itself essentially into that of the action of the moss on some such protein as peptone in the presence of acid, and how such action is modified by the presence of other wort constituents as dextrin, maltose, inorganic salts, etc.  If a solution of Irish moss is added to an aqueous solution of peptone, little or no precipitation takes place until a drop or two of hydrochloric acid is added.  Even with a rough experiment, it is obvious how the physical condition of this precipitate is profoundly modified by the amount of moss and by the amount of acid.

In the majority of experiments a 0*2 per cent, solution of peptone was used as approximating to the concentration of peptone and albumose in an average wort of sp. gr. 1040°.  Fifty cc. of such a solution, after adjustment to certain pH values ranging chiefly from 6*5 to 4*0 by means of added acid, were boiled and various volumes of Irish moss solutions added.  The solution was cooled after boiling and the quality of the flocculation examined.  As in most cases judgment of the quality of a “break” by the eye is misleading, the cooled liquids were filtered through filter paper of open texture, and the clarity of the filtrate together with its pH value observed.  If the filtrate was bright, the particles must have been large enough to be retained by the paper and it could be assumed that the “break” had been good, whilst the varying degrees of opalescence or haziness of the filtrate defined the qualities of more indifferent flocculations.  Some of the results so obtained are found in Table I.

In Experiment I., in the table, when Irish moss was added at the rate of 1½ lb. per 100 barrels to a 0*2 per cent, solution of peptone, the first point observed was that optimum flocculation was obtained when the liquid showed a pH value approximating to 5*2 to 5*3. With more acid and alkaline liquids, the filtered solutions were hazy.  There was, however, a slight difference in the quality of the haze.  With pH values more alkaline than that of optimum clarity, the haze tended to be opalescent, whereas with those more acid the haze was more concrete, and could probably be removed by a filter paper of sufficiently close texture.  A second point, which was obvious, was that the opalescent liquids filtered slowly, and that there was a rapid diminution in the viscosity just prior to point of maximal brightness.

The third point is rather important, as it is connected with the gradual acidification of the wort during fermentation.  It was found that if more acid was added to the filtered solutions, those in the zone of greater alkalinity than that of optimal clarity gave a further precipitation, showing that there had not been sufficient acidity to precipitate completely the peptone-Irish moss compound.  With the brightest solution and with those having more acid or additional acid, unless in large excess, had no effect.  This fact could be, and was, used on occasion to determine the optimal clear point.  Whether a fairly clear filtrate had or had not reached the point of optimal brightness could be determined by the addition of further acid.

     Influence of the Concentration of Peptone.—
Experiments I. and V. show the result of varying the concentration of the peptone in solution, but keeping the other conditions the same.  With 0*2 per cent, and 0*6 per cent, solutions of peptone and Irish moss at 14 lb. per 100 barrels, the point of maximum clarity in both cases lay in the neighbourhood of pH 5*2 to 5*3.  Since similar results were found with other concentrations of peptone, one is led to the conclusion that the position where the best flocculation is obtained is independent of the concentration of the peptone.  This is probably to be expected, since, even with the lowest concentrations of peptone in the experiments in Table I., and those are normal to a brewery wort, there will be ample excess of peptone and similar proteins to interact with all the Irish moss, unless the latter is added in excessive amount.

With all concentrations of peptone, the filtered solutions in the more alkaline zone are more or less opalescent, and produce more haze on the further addition of acid.

     Influence of the Concentration of the Irish Moss.—
Experiments I.- IV. show the effect of increasing concentrations of moss upon the position of optimal clarity when the concentration of the peptone is kept unaltered.  From the results it is at once obvious that the quality of the flocculation is influenced by the amount of Irish moss added.  In all cases there is a point of maximal clarity, but the pn value of the liquid at which it occurs is lower, or more acid, according as the quantity of moss is increased.  The optimum pH values for additions of 1½, 3, 4½ and 7 lb. of moss per 100 barrels may be taken as 5*3, 5*0, 4*8 and 4*5 respectively.  It follows that a peptone solution whose resulting pH value is at 5*3 with moss added at a rate of 1½ lb., will give excellent flocculation, whereas if a 7 lb. rate had been used with the same peptone solution, the “break” would be poor, and the filtrate hazy at that pH value.  It must be noted that an allowance of approximately 0*1 must be made in pH value for the influence of the greater amount of the two added quantities of moss.  In other words, with a rate of 1½ lb. added to a peptone solution, the resulting pH might be 5*3, whereas with the 7 1b. rate added to the same solution, the pH value would approximate to 5*4, i.e., 0*1 greater, owing to alkalinity of the added moss.  In addition, at pH 5*3 further acidification will have no effect with the 1½ lb. rate, but will cause more haze, if the rate had been 7 lb. looking at the problem from the point of view of the acid zone, it is seen that if the original peptone solution had a pH value of 4*5, a rate of 1½ lb. would be insufficient and the liquid would be hazy, whilst, on the contrary, the floeculation would be in the proximity of the optimum with the 7 lb. rate. When the addition of the moss was reduced to as low as ½ 1b. per 100 barrels, a position of optimum brightness could still be obtained, but which was more or less indefinite.  None of the filtrates were clear, and it appeared to suggest that too small an addition gave little or no benefit even within the optimum zone.

     The Influence of Dextrin, Maltose and Glucose.—
Whether the flocculation of the peptone by the moss was affected by the presence of such wort constituents as dextrin, maltose and glucose was next determined.  Would dextrin or other of the carbohydrates act as protective colloids and tend to prevent the flocculation?  It was first noted that dextrin and the other carbohydrates, with or without added acid, were unaffected by the moss in the absence of peptone.

A selection from the results appears in Table II. :—

For any definite rate of addition of Irish moss, although the position of optimum brightness was uninfluenced by the presence of the various wort carbohydrates, a slightly inferior quality of flocculation was produced.  Thus, the optimum flocculation with 1½ lb. of moss per 100 barrels still showed at approximately pH 5*2, but the flocculation itself was inferior to that obtained in the absence of dextrin, etc.

In many cases the degree of flocculation, as shown by the brightness of the filtrates, looked of equal quality at pH values ranging from 5*6 to 4*9.  Yet, such worts might not ferment equally well, for, as already mentioned, additional acidification of those liquids whose pH values exceeded the optimal value (5*2—5*3) for a rate of moss of 1½ lb. per 100 barrels, caused further deposition.  If such precipitation were caused by the acid naturally produced during fermentation, it would tend to coat the surface of the yeast and give rise to possible trouble.

     The Influence of Hop Infusion and Inorganic Salts.—
Neither tannin nor hopinfusion, although they affected the adjustment of the pH values and also complicated the problem by the combination of the peptone with the tannin, appeared to influence to any material extent the positions of optimal brightness.  In this case the filtrates had to be heated to dissolve the tannin-peptone portion of the precipitate, before the clarity of the liquid could be judged.  Whilst sodium chloride was without effect, the addition of calcium chloride gave some interesting results. Although the flocculation was generally less efficient, there was, for the rate of 1½ lb. of moss per 100 barrels, the normal zone of greater brightness approximating to pH 5*2.  But, in addition, the more alkaline solutions instead of showing their usual intense opalescence were almost clear, indicating a better break then that at 5*2.  It was, however, noted that although the flocculation was improved, those clear solutions became very opalescent on acidification and that the solution with the pH value 5*2 stood alone as the optimum, and as that which would be likely to give least trouble during fermentation.

    The Influence of the Cellulosic Insoluble Residue from the Moss.—
The additions of Irish moss in the experiments described previously were made with solutions of the moss, and did not contain the insoluble gelatinous skeleton of the moss.  This gelatinous material might resemble alumina cream, kaolin and other clarifying substances, and might even be the predominant factor in the removal of hazes from the worts.  When all the soluble portion of the moss was removed by extracting for a prolonged period with boiling water, portions of the residual sludge were found to act as efficient clarifying agents when boiled with hazy brewery worts.  The presence of such gelatinous material in the experiments which have been tabulated removed some of the slight hazes recorded, and in place of “very slightly hazy” the result had to be noted as “clear”.  As a consequence, the zone of optimal flocculation with brewery worts where Irish moss is used, is wider then that indicated by the experimental results.  Although, however, the flocculation is improved, there still remains the possibility of danger from the acidification, and from the latter fact which has been emphasised throughout the paper, it must be judged that a good “break” does not always indicate safety.

On occasions, higher proteins than peptone may be present in wort, and that these probably enter more readily into combination with the moss appeared to be indicated by some qualitative experiments on extracts from partly hydrolised barley, and also on extracts made from malts grown two or three days on the floor.  Under those conditions the proteins would be partly unmodified, or, at least at a less degraded stage than peptone.  In both these cases when adjusted to the correct pH the addition of the calculated concentration of Irish moss gave good precipitation and very bright filtration.

It is evident from the results given in the paper that none of the wort constituents, except in so far as they may alter the pH value, have any effect upon the flocculation of the peptone with the moss.  The quality of the “break” depends upon the relationship of the pH value and the amount of added moss per 100 barrels, and is not influenced by the concentration of the wort.  In practice, therefore, the pH value of the wort should be ascertained and the quantity of moss to be added chosen according to that value.  With normal worts, the addition of 4 lb. of moss per 100 barrels will probably be an upper limit and correspond to worts whose pH values approximate to 4*6 or 4*7.  With worts whose pH values are high or above 5*5, it is questionable whether any moss should be added at all.  The flocculation might be improved, but trouble might be stored up to reappear during fermentation.  There must also be a large number of worts of normal pH values, which do not call for the addition of Irish moss.  The grist may have been so chosen and the mashing carried on at a low temperature so that the amount of higher protein is negligible, and the moss has nothing to combine with.  This amount of peptone, however, would require to be abnormal, for, with as low a concentration of peptone as 0*l per cent, and the 1½ lb. rate of moss, the normal results were obtained identical with those given by the higher concentration of peptone.

The flocculation of peptone in boiling wort by means of Irish moss remains practically uninfluenced by the concentration of the peptone and other wort constituents.  It is sensitive to the reaction of the wort and to the concentration of the moss per barrel of wort.  To obtain optimum flocculation, a greater amount of free acidity in the wort must be met with the addition of a greater amount of Irish moss per barrel.  Should too great an amount of moss be added than that required for the pH value of the wort, the resulting wort will become hazy on the production of acid during fermentation, with possible prejudicial effects upon the yeast.  The insoluble cellulosic skeleton of the moss is also an important factor in the clarification of the wort.

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