Saturday, 2 April 2016

Bottled beer in the 1950’s – Bright Bottled Beers (part eleven)

Back with filters. This time looking at one of the two types, plate filters, in detail.

Most brewers, it seems, used pairs of plate filters:

“The former type consists of square grooved plates of gun metal or plastic material between which are sandwiched sheets of specially made filter material of about 0.25" thickness. The alternate supporting and filtering plates are assembled on a square frame and are compressed by a helical screw by which they are packed together. A pump is used to force the beer through; usually driven by a separate electric motor. Filter sheets of different pore size are available and generally the filtration takes place in two stages. In the first, sheets of larger pore size are used and serve to take out the bulk of the insoluble matter, the beer after passing through this 'rough' filter goes through closer sheets which take out the fine particles, giving a bright beer. This final stage is known as the 'polishing' stage. The polishing stage could of course, take out the larger particles as well, but in the absence of a 'roughing' stage it would soon become clogged and its useful life would be shortened. The life of these sheets before they become so clogged as to slow down filtration too much depends upon the amount of insoluble matter in the beer, so the more deposit can take place in the cold conditioning tank the better.”
"Brewing Theory and Practice" by E. J. Jeffery, 1956, page 342.

That seems to make sense. Get out all the rough stuff first, then worry about the smaller crap. It seems good brewing practice was still recommended. If you got most of the rubbish out of your beer at the fermentation or conditioning phase, your filters would last longer.

I hadn’t realised they already had sterile filtration this early:

“The 'rougher' and 'polisher' may be separate filter assemblies or they can be combined in one plant, the beer passing successively through both sections. Careful research by the manufacturers of the filter sheets has resulted in grades which produce not only a brilliant beer but one which is virtually sterile, in fact if properly used they can produce beer that will keep free from growth of any organisms for indefinite periods. Possibly a few of the smaller acetobacter may get through but conditions in bottled beer are not favourable to their growth. The wild yeasts and the majority of bacteria are filtered out. Many bottlers rely entirely upon sterile filtration for adequate shelf life for their beers. It is important that the filter itself does not impart any organisms to the beer. For this reason the plant is sterilized before use by passing hot water (180º F.) through die plant and the mains through to the bright beer tank or filter for at least 15 minutes.”
"Brewing Theory and Practice" by E. J. Jeffery, 1956, page 342.

I’m impressed that they had filters capable of leaving beer virtually sterile. That must be a pretty damn fine filter if it’s taking out almost all the bugs. I guess it meant that there was no need to bother pasteurising. If it was already sterile why waste the energy pasteurising?

That you should keep your filters nice and clean seems pretty obvious if you expected the beer to be sterile after filtering.

“After use the filter should be well washed with hot water and then sterilized again before re-use. An important precaution is necessary if the washing water is alkaline or has appreciable temporary hardness, where the beer is run direct from filter to filler. The alkalinity may be adsorbed upon the filter fibres and then given up again to the first beer which is passed through. The operative will reject the first runnings which are obviously diluted with water, until it is obvious that the beer has replaced the water. However, even when the water has been displaced, the first few barrels of beer may have their pH raised considerably with unpleasant results upon their keeping qualities. Therefore the first few barrels should be returned to the bulk in the tank where any alteration of pH will be swamped by the large volume of beer. An extreme instance of this occurred when some dozens of bottles of beer which had first come through the filter had pH values as high as 6 or 7, their flavour was insipid and they acquired a putrid smell on keeping due to growth of bacteria which could not have developed in a beer of normal pH. This difficulty only arises when bottling direct from the filter, as if the beer is returned to a bright beer tank the first few barrels are ipso facto mixed in with the bulk.”
"Brewing Theory and Practice" by E. J. Jeffery, 1956, pages 342 - 343.

That’s in interesting way of rinsing out the cleaning liquid from the filter – run beer through it. Though I’m sure that they’re correct that spread over the whole tank, whatever cleaner residue was left in any one bottle would be negligible. Let’s just hope it wasn’t anything too toxic.

Finally another encouragement of good brewing practice:

“After the passage of several hundred barrels the sheets will become clogged and the throughput will drop, until the pace is too slow to be economical. The pressure of the liquid will tend to rise and a point may be reached where slight local breakdown of the filters occurs, which, even if not sufficient to affect the brightness appreciably, may result in leakage of infective organisms to the detriment of the keeping qualities. It is therefore desirable to ensure as much deposition of insoluble matter as possible in the cold storage tanks, and to use the roughing filter for the removal of the bulk of the insoluble matter still suspended in the beer.”
"Brewing Theory and Practice" by E. J. Jeffery, 1956, page 343.

You might save a little time by rushing beer through the conditioning tanks. But if it meant you had to keep changing your filters, or worse, you bottled beer that wasn’t sterile, it could end up costing you more in the long run.

Kieselguhr filters next time.

1 comment:

Ed said...

The filter at work still uses a combination of fine and coarse filter pads.

Sterile filtration is good, but is potentially more problematic than pasteurisation. With a tunnel pasteuriser the beer is in sealed container when it's pasteruised so there's no chance of further contamination. With sterile filtration once the beer has left the filter then everything else (e.g. pipework, buffer tank, bottle filler, bottles, caps) need to be aseptic or the beer will get infected by bugs.