MEETING of the YORKSHIRE and NORTH EASTERN SECTION, HELD at the QUEENS HOTEL, LEEDS, on THURDSAY, OCTOBER 28th, 1926. Mr. J. C. Radcliffe, B.A., in the Chair.
The following paper was read and discussed: —
FERMENTING VESSELS: THEIR ADVANTAGES AND DISADVANTAGES.
By William Collins.
During the past few years nothing connected with brewery plant has been so much discussed as fermenting vessels, and probably this has been brought about by the change in the gravity of the beers and the necessity for avoiding any risk of contamination from the vessels in which low gravity worts are fermented. In consequence, the Yorkshire Square which rendered good service before these light gravity beers came into vogue, has now come in for a great deal of criticism and abuse, and in many cases has been abandoned in the brewery as a dangerous vessel and a thing of the past, and replaced with either copper, aluminium, concrete or glass lined vessels. This is done not because a better flavoured beer will be produced, but because such a beer will retain its good palate flavour for a longer time than would otherwise be the case.
It is in the fermenting vessel, particularly towards the end of fermentation, that a beer may become infected, and from that point of view a sterile surface very much lessens the opportunity of contamination and pro longs the life of the beer.
The advantages claimed for the closed Yorkshire Square is that the beers fermented in them drink about 1 lb. heavier and are usually in better condition than a similar beer from an open vessel, and these two advantages appear to be about all that is claimed in their favour. In the writer’s opinion, any advantages gained from the Yorkshire Square are not compensated for by the disadvantages.
One of the chief objections nowadays to the Yorkshire Squares is that they are so small that it takes several vessels for the days brewing, and with so many corners and crevices to deal with during the washing out process it is nearly impossible to get all of them clean and in a sterile condition.
If worts are run into 8 squares of 30 barrels each, there are 96 corners to contend with, besides the racking cocks, striking taps, organ and back-drink pipes to keep thoroughly clean, instead of 8 corners and 2 racking cocks, if the brew was run into 2 vessels of the open type of 120 barrels each. Another disadvantage of the Yorkshire Square is that the cleaners have so little room to work in, and the light inside the vessels is so poor they cannot well see what they are doing. It is also impossible to use very hot liquor, as this renders the work difficult owing to the steam, and in the case of closed slate squares it is prohibitive for fear of cracking the slabs. Thus, caustic soda, or some other preparation for cleaning out the fermenting vessels has to be employed.
A solution of caustic soda and yeast is quite useful for stone and slate vessels, as it sets in the form of a jelly on the sides of the squares and does not dry off so quickly as when using caustic soda solution by itself.
It is impossible to sterilise a bad joint in a stone or slate square, and as it gradually begins to crack or break away, a wort soon becomes heavily infected with foreign organisms before the pitching yeast has an opportunity of activity.
A further disadvantage of the Yorkshire Square is the amount of waste to deal with in the shape of tops and bottoms, without mentioning “back-drink,” the constant attention and supervision several small vessels require with the working heats, and the pumping, rousing, running off “back-drink” skimming, etc.
As regards the beers drinking 1 lb. heavier, several firms who have changed from the closed to the open system of fermentation have not noticed any real difference in the fulness of the beers by the changed methods, and it is difficult to understand why there should be any difference if the same type of yeast is used and the same rate of attenuation maintained. It is, however, probable that a beer fermented with a slow yeast drinks fuller than one fermented with a quick type. It has been said that it is not possible to maintain the character of a Stone Square yeast for more than three months’ when worked in open fermenting vessels, and consequently if all the closed Yorkshire Stone Squares were done away with, the character of this yeast would go also; this, however, has not yet been proved. It has not. been put forward that a Burton Union yeast loses its character when worked in open vessels, and it is difficult to appreciate where the alteration would come about with a Stone Square yeast. The probability is that the character of Stone Square yeast would be maintained if the materials are good, and close attention is paid to working heats, pumping and re-submersion of the yeast head.
At the Brewery with which the writer is connected there are several closed Stone Squares of 30 barrels each, and some open fermenting vessels of 130 barrels each, and it invariably happens that the Stone Square finish 6-8 hours earlier than the open vessels, this result, no doubt, being partly due to the more effective pumping in the small as compared with the large vessels.
Probably there are few brewers using the Yorkshire Stone Square system who have not altered the methods of pumping the squares in some form or another, and who have not replaced the old hand barrel pump and plunger by some-mechanical pump and sprayer. It would be interesting to know if these alterations were reflected in the character of the yeast. The writer has observed when working Stone Square yeast in open vessels that it is necessary to attenuate a little lower in the latter vessel, otherwise the finished beer is inclined to drink slightly yeasty.
Working with a slow yeast, the attenuation can be so controlled that it is possible to rack at almost any desired gravity, whereas with a quick yeast the attenuation is not so much under control, and sometimes the racking gravity will be down to l/5th and even 1/6 of the original.
With Stone Square yeast the aeration of the fermenting wort is not of so much importance as the re-submerging of the yeast head, for if the spraying is inadequate some cells become granulated and die off through being deprived of proper nourishment. The rousing in the larger vessel with the slow yeast must be arranged so that the whole of the yeast head is beaten ack into the wort for further nourishment with each rouse.
With regard to the materials and construction of fermenting vessels, wood has rendered good service for a great number of years and is still preferred by many brewers. That it is not a good conductor of heat is a point in its favour with the slow yeast worker.
Whatever timber is decided on it must be thoroughly seasoned and free from knots. The object of seasoning is partly to evaporate the sap and partly to reduce the dimensions of the wood, so that it may be used without further shrinkage. Wood fermenting vessels have this drawback, that unless they are con structed with thoroughly seasoned material they are liable to open at the joints if they happen to be put out of use for a few days. Oak has obtained a pre-eminence, as it is hard and strong without being too heavy, and not readily penetrated by water. Oak is mostly used in the direction of rounds, and owing to its hard nature, if rubbed over on the inside with a pumice block each time the vessel is emptied, a smooth almost polished surface may be maintained. Kauri pine imported from New Zealand is a timber held in much esteem for fermenting vessels. Unfortunately, the supply of really first-class material is very limited. It is a hard timber, fairly free from knots, and possesses a good finished surface. Teak, although not quite so hard as Oak and Kauri pine, is an excellent wood, and is strong and durable. It is easily seasoned and shrinks but little. Fermenting vessels may also be built of Columbian Pine, Red Deal, Cedar, etc. Cedar wood, although sweet smelling, is rather light and brittle, and care is required that the workmen do not chip or injure the surface when washing and climbing in and out.
Even with the greatest attention, wood vessels are not easy to keep in a sterile condition, as the moist surface provides a suitable medium for the development of foreign organisms which retain their vitality for a long time in the pores of the wood, and it is general experience now that wooden vessels after only a few years use are always liable, to contaminate the beer to a greater or less extent with secondary yeast or bacteria, the former generally in a new vessel and the latter in an old vessel. Many brewers get over this difficulty by lining the inside of the vessels after they have been in use for three or four years, and if a metal lining is used the bottom sheets should be thicker than the sides as the wear and tear is mostly on these. Scale should not be allowed to accumulate on the surface of any fermenting vessel, and there is no excuse for allowing it to do so, as it is easy to keep down if thoroughly scoured with pumice or treated with a weak alkali each time that the vessel is emptied.
Slate would appear to be a most useful and desirable material for the construction of squares, but for some reason or other it is not often used now. The one objection to slate is the difficulty with variations in the outside temperature, but this could be overcome by lagging on the outside with plastic cement or with some other non-conducting material. Owing to its imperishable and impervious nature, its hard, smooth surface is easy to keep clean and can be scoured out with, fine pumice to any extent without injuring its surface, or it can be treated with alkali. Slate does not injure the yeast or affect the flavour of the beer and needs no lining of any description. It is practically fool-proof and does not require anything like so much care bestowed upon it as do some other kinds of fermenting vessels. Different slates vary considerably in hardness, and only the best Welsh should be used.
Aluminium fermenting vessels are well spoken of and are fairly easy to keep clean, and in a sterile condition. In the past this metal has been known to give trouble through pitting, but this has now been largely got over, and solid aluminium vessels can now be erected with a guarantee for a number of years. Scale accumulation on these vessels appears to be rapid but can be prevented from forming on the surface by the use of a special bronze brush or scoured with fine pumice. To keep the surface of aluminium vessels in perfect condition they should be cleaned immediately as they are emptied, drained and left standing dry.
No alkali must be used on Aluminium vessels, and mercury thermometers should be replaced by spirit indicators.
Copper fermenting vessels have been objected to owing to the weakening or toxic effect on the yeast. This opinion was often expressed 20 years ago, but is now fast dying out, and there are in fact copper lined vessels in use to-day which formerly were believed to affect the yeast. Copper fermenting vessels have been in use—especially in Scotland—for many years, with no trouble of any kind and where lagged solid copper vessels are erected they have been found to give good results. The brewer’s fear of this metal appears to be rapidly disappearing. In nearly every case where trouble has been experienced with copper, it can be put down to scouring the vessels with pumice powder. Copper vessels should not be scoured, but merely scrubbed with a solution of common soda. Copper has one advantage over linings, and that is they are smooth throughout, whereas owing to expansion on the copper-lined vessel, where thin sheeting has been used it often becomes wavy especially at the bottom. Copper is not affected by water, but tarnishes on exposure to the air, and becomes covered with a green carbonate, which, however, is not harmful to the beer. Glass enameled fermenting vessels have of late years claimed attention, although they are more often used for storing beer than for actual fermentation. The basis of all kinds of enamel is glass, fused to the surface of metal or other material; a few brewers in this country have used glass enamelled closed vessels of the Yorkshire type. When new, the glass enamelled surface is excellent, and, of course, perfectly smooth and easily rendered sterile, but it is a good conductor of heat, and being brittle and easily damaged it requires very careful treatment. Glass enamelled vessels should not be cleaned with strong acid or alkali, and it is of the utmost importance that all yeast and sediment should be well washed off the enamel before it is allowed to dry, as if this is not done the surface soon becomes stained and a hard, yeasty scale forms which spoils the appearance and sterile nature of the enamel.
Concrete fermenting vessels have been in used on the Continent for a number of years, and recently a few have been erected in this country. The inside of these vessels have to be lined with a material that is not penetrable as concrete is rapidly attacked by the acids of fermenting worts. The lining of these vessels in the past has been a difficult problem but it is now claimed that a suitable lining has been discovered, and which fully answers all the brewers’ requirements. Until recently some linings for coating the inside of concrete vessels were not satisfactory and required repeated application of the material to keep the vessel in proper working order. Concrete is not such a good conductor of heat as is slate, and the unlagged aluminium and copper vessels, but they require very great care when erecting and only skilled and experienced firms in this class of work should be employed.
With several different types of fermenting vessels to choose from, and with such a diversity of opinions as to the most suitable vessel, it is not an easy matter for those contemplating alterations to fermenting plant to decide what kind to erect. Perhaps none of the vessels mentioned are perfect, but each of them has some advantage or disadvantage over the other, and from the brewing point of view, that is to say, the certainty of keeping the beer from infection, those vessels having hard, durable and perfectly smooth surface appear to be equally good.
Crescent City Brew Talk 