THOUGHT PIECE the carling team

How To Make Beer – Getting The Beer Bright

The only additions before filtration might be the use of isinglass finings to remove any remaining yeast and protein from suspension more rapidly than relying on natural sedimentation through a depth of perhaps 10 metres. Without finings you may have a couple of hundred barrels of hazy material at the base of the tank; this is best transferred to a side vessel which is then bled into the brighter beer on its way to the centrifuge for a more even flow of haze and faster operations.

The cones of deep conical bottomed conditioning tanks

Chilling only will protect the shelf life in the marketplace for a couple of months so for beers with longer declared shelf lives on bottle and can products more protein and/or polyphenol should be removed. Some brewers aim to adsorb protein molecules into interstices of added silica hydrogel which is subsequently filtered out. Indeed some will dose the hydrogel into the filter although vessel addition will allow a longer reaction time.

In days gone by brewers might have added papain which is a proteolytic enzyme to break down the protein molecules into smaller units which would not cause beer hazes. However, beer foam is also a protein so the practice was somewhat counterproductive. Today we know a lot more about which types of protein that cause beer hazes. There is an enzyme in common use today called Brewers Clarex which is a proline specific endopeptidase which means it will cleave protein molecules containing a proline amino acid unit. It has been shown that such proline containing protein units will react with polyphenols and precipitate a haze. Remove the proline and the polyphenols have nothing to react with hence no haze. Incidentally the same proline rich peptides cause coeliac symptoms so its use can produce ‘gluten reduced’ beers for that market sector.

Longer shelf life products would demand the removal of some polyphenols as well and that would be accomplished by adding polyvinyl polypyrrolidone (PVPP) which acts like a protein molecule and complexes with it and thus removes it from suspension. These treatments are expensive and as PVPP can be regenerated using sodium hydroxide, it is better employed for smallpack beers by dosing it into a second smaller filter after the main unit where the material can easily be recovered for regeneration.

Horizontal maturation tanks needing a ladder to reach the sampling point.

Many brewers of course do not use deep conicals and will condition in smaller horizontal tanks. The stresses and strains of supporting such tanks are complex and so a 400 barrel vessel would be a large one although the Americans have some giants. They would slope slightly forward to the outlet which may have an upstand to hold back sediment or else be fitted with an internal swinging arm so that the operator could filter brighter beer from the top of the tank first and gradually empty the vessel by moving the arm. Manning levels today probably preclude such niceties but brewers should never forget the watch-word that ‘you should not try and filter hazy beer’ as it will shorten the filter run forcing you to use more filter powder and go into a time consuming wash off earlier than necessary.

So now the beer is brightish and can be fed forward to filtration. A centrifuge with a tighter plate pack may be used to remove finer protein particles at 1μ rather than the type used earlier to remove 7μ yeast cells from the green beer in fermenter. This is all geared to maximising the volume of a filter run.

Photomicrographs of kieselguhr on the left and perlite

Classic beer filters use an inert powder which is built up on a matrix supported on a paper pad, mesh or wire wound around vertical tubes called candles. Powder is continuously dosed into the beer flow and particles get trapped in depth and the filtration must stop when the chambers fill completely. Thus brighter infeed means less dosage and longer filter runs. The powder can be perlite which is ground up volcanic pumice or else kieselguhr which is a non renewable resource of fossilised sea creatures. Although a better filter medium, the latter has a grade four respiratory hazard rating involving aspirated bag slitters and face protection so perlite is widely used. Even perlite is dusty and needs making up into a slurry to dose into the beer flow so the industry is moving towards powder free cross flow filtration where the flow of beer keeps the filter surface clear while high pressure forces the liquid through ceramic or polyethersulphone membranes.

Candle filter and on the right the built up filter powder has been scraped away to show the white coarser precoat layer and gaps in the vertical candle.

Once filtered the beer will be diluted with deaerated water and will pass through a pressurised carbonator to adjust the CO2 content to 2 – 2.5 volumes depending on whether it is going to keg or small pack. Another pressurised unit can add nitrogen to 35ppm, smaller bubbles of this gas create a desirable tight head on the beer in the glass and in ales it reduces the level of CO2 needed thus these ‘smooth flow’ beers are creamier and are less ‘fizzy’ than traditional lagers. Nitrogenated keg beers demand some nitrogen in the gas pressurising the keg in the cellar thus adding more complexity to the modern beer cellar which we shall discuss in a forthcoming blog.

A plate and frame filter builds up the powder supported by cellulose pads. The disadvantage is the labour intensive job of regularly replacing the support pads

The presentation of the beer in the glass is an important attribute in the marketplace. Nitrogen gas will produce a nice white foam in the glass or the brewer can use wheat in the grist to improve the head and there are even hop preparations which add bitterness as well as enhancing beer foam. However he also needs to reduce any foaming throughout the process to make sure the foaming potential remains intact up to the customer’s glass. Antifoam will prevent over foaming in fermenter but modern rapid wort separation is prone to transfer some head negative molecules so a dose of perhaps 50ppm of E405 – propylene glycol alginate (derived from seaweeds again) into bright beer tank gives that little bit of extra protection. Don’t worry it is a major component of ice cream and salad dressings as well!

All our additions are now in. We have added auxiliary finings, isinglass finings, silica hydrogel and polyvinyl poly pyrrolidone. Brewers call these additions ‘processing aids’ as you can see they complex with molecules in the beer we are trying to remove and settle out or else are filtered out. None of them are present in the finished beer (apart from the E405) so you can see why brewers are reluctant to accept these as ingredients which should be displayed on any future labelling legislation. What about carbon dioxide or nitrogen? It is a minefield!

A Pall Profi membrane filter and to the right a cross section of the tubes. Third along is a ceramic system from Alfa Laval and far right a pair of sterile pad filters at a smaller plant