Saturday, 3 January 2015

German brewing in 1966 – filtration

We’re fast approaching the end of the article and this series. But don’t despair. I’ve another article from a decade later to continue with once this one is done.

Filtration – what a, er, dull topic. As a cask beer man, I’ve always thought of it as the work of the devil. Though I do realise that bottle-conditioned beer is usually filtered and then reseeded with yeast.

This should be pretty quick because I can’t imagine I’ll have much to say. Which is rare for me. I’d make the most of it if I were you.

Filtration and Stabilization
The changes in the consumption of beer and the distribution through supermarkets and direct delivery to the home have increased the requirements for biological and physico-chemical stability of the beer. For this reason simple kieselgur filtration is no longer sufficient, despite the fact that by this means a shelf-life of 3 weeks can be reached, which is sufficient for cask beer. Despite the use of carefully-calculated initial coating mixtures plus the addition of asbestos and even with careful mains dosing at reduced output (2.5 hl. per square metre), it is not possible to remove all yeast from the stored beers and this has resulted in yeast hazes in the bottle.”
Journal of the Institute of Brewing, Volume 72, Issue 1, January-February 1966, page 23.

Interesting that changes in consumers’ buying habits – bottled beer from the supermarket ousting draught beer in pubs – caused a change in brewing practices. Of course, in a beer that’s supposed to be crystal clear, any sort of sediment is a pretty bad fault. Presumably the average time between packaging and consumption increased considerably when supermarkets got involved. Lots of time spent hanging around in warehouses.

I can remember Czech bottled beer from the communist days having a very short shelf-life. After a couple of weeks a sediment would form. Not a problem for Czechs, as they didn’t leave beer hanging around undrunk for long.

“In many cases the old pulp filters were brought into use again. The labour requirement is very high as regeneration of the pulp is necessary after each use. Nevertheless, a considerable increase in stability could be obtained by pressing the pulp at 5 atm. And adding 0-5% asbestos whilst at the same time slowing down filtration to 1 hl. per cake. Other breweries use as a final filter the new cotton candle filters whose output is calculated at 1 hl. per hr. per candle. The ability of these filters is limited but they are useful for obtaining the required sterility and the absolute output depends on the size of the pores. Output also depends on the constitution of the beer, and on the pre-filtration and type of sterilization and regeneration (2% caustic soda with hydrogen peroxide).”
Journal of the Institute of Brewing, Volume 72, Issue 1, January-February 1966, page 23.

1 hl per hour is effing slow if you’re brewing on an industrial scale. You’ll be there for ever trying to filter a 200 hl tank.

I always find the mention of asbestos scary. I was going to ask if it was still used for filtration purposes. But why speculate when I’ve Briggs to hand:

“Filter sheets were originally made from a mixture of cellulose and asbestos fibres. Sheets have also incorporated kieselguhr for over 70 years. Recently perlite, glass fibres and cotton fibres have been used. Asbestos is not now used because of the carcinogenic properties of some types of asbestos. It is fair to comment that the elimination of the use of asbestos took a long time in many breweries. Asbestos was useful because it offered adsorption through electrical charge as well as surface filtration. This has been replaced in some applications by the incorporation into the sheet of aluminium oxide or zirconium oxide fibres.”
"Brewing: science and practice", by Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes and Roger Stevens, 2004, page 576.

So, no, but it took a while. I’m glad I drank beer that hadn’t been filtered in the1970’s and 1980’s. No need to consume carcinogens unnecessarily.

This part of the article is demonstrating an important point: the brewery technician’s interest are focused differently from mine. The section on filtration and stabilisation is as long as that on the brewing process, something that I would have preferred more detail on.

“The biological results are satisfactory even though the effect of a very carefully controlled pulp filter is not quite achieved. The cotton cylinder filter has proved to be particularly useful as a final filter after kieselguhr sieve filters. Nevertheless, a further biological improvement in the beer can be achieved by means of sheet filters or pasteurization.

Despite the automation of the flash heat-exchanger units some breweries prefer the sheet filter for improving shelf life. By means of careful filtration, sufficient calculation of the filtering surface, observation of the pressure conditions, and possible control by means of a graph, a very stable beer can be produced which will even be suitable for long distance transport. By these means, detrimental effects on flavour will be less than with pasteurization and the detrimental effect on head stability is marginal.

Nevertheless, the sheet filter has to be opened every day or every second day and the price of the sheets is high. E.K. sheets have an output of only 1-1.5 hl. per square metre—i.e., in total, approximately 12 hl. On the other hand, if one selects the so-called clearing sheets then the output can be increased at the cost of reduced biological filtration effect.”
Journal of the Institute of Brewing, Volume 72, Issue 1, January-February 1966, page 23.

Right. Sheet filters were a way of getting a beer that was near-sterile without pasteurisation. Which as we all know can bugger up the flavour of a beer a treat.

Briggs also points out the lack of throughput in sheet filters;

"The standard filter sheet in breweries is 60 - 62 cm and the largest normally 100 - 100 cm. A large single-ended filter press would have 240 filter plates allowing a filtration rate of 120 hl/h. This low throughput rate has limited the use of sheet filtration for primary filtration in large breweries. Sheet filters are now usually used only as second polishing filters following depth filtration with powders or are dispensed with completely."
"Brewing: science and practice", by Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes and Roger Stevens, 2004, page 576.

That sounds better, because large numbers of filter sheets were being used. Even 120 hl. per hour is still pretty slow.

Just pasteurisation and bottling to go.

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