Wednesday, 8 October 2008

The dropping system of fermentation

I'm such a populist. I should try choosing more obscure topics. Or you'll start calling me the Daily Star of beer blogs.

I was much intrigued by the dropping round and settling square kept as a museum piece in the Fuller's brewery. For one thing, it gave me chance to see exactly what an attemperator looked like. And the brewer, John Keeling, explained to me how it worked. He told me that the wort was usually dropped after 12 hours or so. The exact timing being determined by the type of head that had formed.

The Fuller's logs are full of information. Including complete fermentation details. And they tell you when the beer was dropped. Looking at their bog-standard X Ale, that's exactly what happened. It spent just 12 hours in the round. As did the Porter and Brown Stout. The PA stayed in the round longer, 41 hours. But the AK I have the log for was in the round 66 hours.

The fermentations for the PA and AK are quite different from those of the other beers. The majority took place in the round. About two thirds of the gravity drop was in the round. For the darker beers the fermentation had barely started when the wort was dropped into the square.

Could it be that time in the round was connected to the degreee of attenuation? The AK is the most fully-attenuated.

You'll notice that the fermentation of AK took considerably longer, despite it having a lower OG. Thirty hours longer, to be precise. Before you ask, both the X and AK were brewed at the same time of year. The AK was brewed on the 14th March 1910, the X 10th March 1910.


Andrew Elliott said...

It appears that they are dropped into the round fairly cool. This would slow down the yeast's metabolism and cause a longer fermentation time, but perhaps a smoother character with fewer esters?

Also it looks like the AK only spends 6.5hr in the square vs. the X for 29 hours. I wonder what effect this had on the beer.

Interesting stuff!

-Andrew Elliott

Anonymous said...
Page 805 and 806 has a description of dropping

Kristen England said...

These 'old' systems really intrigue me. The 'cleansing system' being the oldest which was basically a single fermenter where the beer was cleared in the casks.
The 'dropping system' is just a minor modification of the 'skimming system.' Both of these used two vessesl and then the cask. You could make much brighter beer this way.

So to your question, Ron.
What about the amount of yeast used per barrel? Same goes for the percentage of sugar?

The AK states that it uses 57lb 1st crop. How does the X differ?

I'd put dollars to doughnuts and bet it wasn't anything like this. Im betting it was a function of two things. The 'head' and the temperature. 70F seems to be the magic number then. They wanted to wait until they got to the 'yeasty' head before they dropped the beers but temperature would regulate it most.

These beers should have been cooler b/c it was March. In the summer Im betting they got them into the squares faster and jacked up the attemperators (sp?).

When the beers started to look like they were almost complete the attemp were cranked to drop the beers down to 60 or low (winter).

At this point they were very careful about skimming in that they wanted to ensure a small head was left on the beer to avoid aerial contamination.

This is combined info from a bunch of 1880-1920 manuals. Lots of good stuff.

Kristen England said...
This comment has been removed by the author.
Ron Pattinson said...

Kristen, yeast per barrel is in today's post. It's not 57 lbs, BTW. That's what I thought at first. It's the first crop from brew 57. The AK was brew 60. The actual weight of yeast was 122 pounds.

All the beer were brewed in March, except the PA which was August. I can't see any difference in the temperatures.

I wonder what "liquor on" means?

Kristen England said...

Where did you see 'liquor on'? I would take it as the time they started the sparge water running (e.g., hot liquor).

Anonymous said...

Kristen: 'liquor on' can't mean the sparge water, because it's towards the end of the fermentation, shortly before racking (you can see it in this photo from Ron's AK post earlier this week). I've no idea what it does mean though...

Ron: I've got a theory on the variation in dropping times. It strikes me that the darker beers have the shortest time in the rounds, as well as being the least attenuated. I'd expect the grists for these beers to produce a higher proportion of more complex sugars (and they may also have used less maize and sugar than in the paler beers), making the wort more suitable for the early phase of yeast multiplication. So it could be that the yeast head formed more quickly on these beers, thus prompting the brewers to drop them earlier. Maybe someone who knows a lot more about fermentation than I do (Kristen?) can tell me if this makes any sense.

Jim Johanssen said...

I think “Liquor On” is the running of cold liquor in the attemperator to cool down the beer to stop fermentation and drop the yeast out of suspension. It is common to drop the temerature 10F or more to control attenuation and clearity.


Kristen England said...


I didn't see that in the photo. In that instance I would definitely agree with Jim about the attemp being turned on.

As for the dark malt thing, there is nothing inherent in the dark malts that would make you change fermentation times in the rounds specifically. Having said that, as I mentioned before, one can change the finishing gravity of their beers in numerous ways. One of them is getting them off yeast (racking, dropping, etc). This is definitely a possibility.

Anonymous said...

This discussion is about a sample size of 1 log. I was wondering whether it is this typical over a period of time? There may be other things to consider - there may be non brewing reasons affecting the fermentation times and use of rounds i.e. demand for the beer or the capacity to be able to package. Is AK a high demand running beer in this period?

Ron Pattinson said...

korev, very good point. Sample size of one, very bad.

When you have limited time, it's easy to just photograph a minimum of logs. I prefer to have at least two of each beer. At Fuller's, I went for as many years as possible. It's not a public archive.

What I've seen from the logs from other years, is that the AK that spent so long in the round was very unusual. but I've not quite got through them all yet.