Tuesday, 30 December 2014

German brewing in 1966 – fermentation (part one)

Not too far to go now. Before you know it we’ll be done and I’ll have to think up another interminable series.

Were now at one of the most vital phases of beer production, fermentation. Where the yeast works its magic and turns dull sugars into exciting alcohol. My favourite constituent of beer.

The Main and Secondary Fermentation
During the last ten years exact control of fermentation has been made possible by the use of suitable flocculating and non-flocculating yeasts. The characteristics of a large number of yeasts were known and it was possible to obtain small quantities of yeast in optimum conditions from the appropriate institutes. However, the quantities required were occasionally so large that even smaller breweries could introduce their own yeast culture plants. The main fermentation was carried out at 5-9° C. for 7-12 days. Yeast was pitched at a rate of 0.3 and 1.0 litres to the hl. and the usual intention was to reach 90% of the final attenuation in the fermentation cellar.”
Journal of the Institute of Brewing, Volume 72, Issue 1, January-February 1966, page 20.

Contrast that with a typical top fermentation:

“The wort is pitched as soon as possible using pressed yeast at a rate of 0.15 to 0.30 kg/hl (0.5 to 1.0 lb/imp. brl). Traditional practice is to pitch at 15± 16º C (+-60º F) and allow the temperature to free rise to 20-24º C (68 to 75º F, Fig. 14.1) as fermentation proceeds. This is rapid and normally finishes in around 48 hours.”
"Brewing: science and practice", by Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes and Roger Stevens, 2004, page 528.

Having spent many a happy hour looking at fermentation temperatures in brewing logs, I can say that Briggs is bang on the money there. Though four or five days is a more typical duration for primary fermentation.

It’s a bit difficult to compare pitching rates as one is given as a weight and the other as a volume. However, it’s obvious that 1 litre of yeast is going to weigh considerably more than 300 gm. The much higher pitching rate for bottom-fermentation is presumably why it was worth the while of even small breweries to have their own yeast propagation system.

Now on to secondary fermentation, or lagering:

“The secondary fermentation at a temperature of +4° to 0 or -1° C. continued for 8-12 weeks. The desired final degree of attenuation was not always reached, so a certain percentage of non-flocculating yeast was used as secondary fermentation yeast or alternatively one, added 6-10% of a two-day old primary fermentation beer. When these methods were properly applied, beers of excellent quality could be obtained. In classic fermentation systems one requires large fermentation rooms with a capacity of one-twenty-third of the yearly output. The storage cellars require a capacity of one quarter of the yearly output in order to allow for the summer peak. These methods are today still used in the breweries of Dortmund and Munich as well as in many other large and small breweries, where every increase in capacity of 1000 brl. per year results in a corresponding increase in the fermentation and storage cellar. Other breweries are looking for a way to avoid new building and as a result of replacement of wooden storage casks with modern tanks a considerable increase in the brewery's capacity can be achieved without difficulty, as a storage period of 8-12 weeks still enables certain reserves to be made available. In addition, fermentation and storage might be saved by cold filtration of the wort, but even this method gives a minimum of 1 week's main fermentation and 4 weeks' secondary fermentation.”
Journal of the Institute of Brewing, Volume 72, Issue 1, January-February 1966, page 20.

The first part of the paragraph is a description of the classic method of brewing Lager. A cool primary fermentation followed by a long, slow secondary fermentation at around freezing.

Adding young, fermenting beer is usually called “kräusening”. The only real record I have of this practice is from Amsdell, an Ale brewery in Albany New York, from around 1900. They were adding a far larger volume of Kräusen – about 25%.

I wonder where that figure of one-twenty-third comes from? I presume it’s based on a batch taking approximately two week in primary fermentation. The one quarter for the lager cellar is easier to work out. If beer was going to be lagered for three months, you’d need about three months’ worth of beer in the lagering cellar.

Reducing the fermentation time is an obvious way of saving money. Nowadays I’m sure the big industrial brewers rush their Lagers through in less than five weeks. I’m not sure that they even lager at all really.

Here’s what happens when the fermentation is rushed too much:

“Frequently attempts were made to obtain a quick fermentation by increasing the pitching quantity and the fermentation temperature (9-12° C.); usually the secondary fermentation intensity was no longer satisfactory as the yeast adapted itself to the higher temperature and received quite a shock as a result of the quick cooling in the storage cellars. The unsatisfactory second fermentation produced beers with insufficient maturity; by-products of fermentation were evident in greater quantities and reduction of diacetyl and acetoin was unsatisfactory. The beers had an unfinished yeasty flavour, a rough bitterness and insufficient CO2 and head stability; continuously changing character and insufficient secondary fermentation affected the normal increase in colloid particles and protein deposits which is necessary for the stability of the finished beer. In these cases an improvement in quality had to be obtained by means of increased use of filter aids and absorption-stabilizing media, in order to obtain beers with the required characteristics. In this connection, it was also useful to replace a large part of the flocculating yeast by non-flocculating yeast which, however, caused difficulties with beer filtration.”
Journal of the Institute of Brewing, Volume 72, Issue 1, January-February 1966, pages 20 - 21.

9-12° C isn’t far off a top-fermenting temperature. No surprise that the yeast didn’t like being chilled down to near-freezing after getting used to the warmth. But I wonder how many of these faults are present in today’s mass-market Lagers? Maybe not the diacetyl, but I’ve had Lagers with rough bitterness. When you could spot the bitterness, that is.

Next time we’ll be looking at newer methods of fermentation.


Barm said...

I suspect that mass-market lager beers would display some horrendous off-flavours if they weren’t mostly removed by the very heavy filtration used nowadays. I doubt that Stella Artois or Heineken will be launching an unfiltered version any time soon.

Ed said...

I've heard a big lagers brand is now fermented at 17.5 degrees C, and some may be even higher.

Barm said...

Of the beers I have hard facts for, Tennent’s is fermented at 13–15C and gets an epic two days of cold conditioning. Heverlee (C&C's competitor to Stella) ferments at 15C and is lagered for two weeks.