Attenuating circumstances

Physics, chemistry and biology of brewing. The causes and the effects.

Moderator: slothrob

Attenuating circumstances

Postby jayhawk » Tue Nov 05, 2002 10:28 pm

Lately I have been having great attenuation. Perhaps a little too great. My latest pale ale batch is down to 1005 (OG 1050) after 6 days fermenting. I pitched on top of the slurry of a porter, so fermentation began quick. According to the 'Tools, this batch is running 88% attenuation, which seems extremely high for British Ale (Wyeast).

My first suspect in this caper is my thermometer. It reads 97C at boiling, even though water boils @ 100C. I shot for 68C mash in, but my thermometer read 71C. I added some cold water and settled for 65-67 C for 60 mins. Is this mash temp, relative to the desired 68C, low enough that I would get such high attenuation? Is there a way to calibrate a thermometer?

Another thought I have is that it could be that some wild yeast has hitched a ride and started to take over this batch. The beer lacks body, but the flavour is still good, so it is not a bacterial infection. The porter prior to this is within normal attenuation range and tastes great. I did have a mishap with my chiller, so I had to let this batch cool on its own for 8 hours proir to transferring to the primary. Any thoughts?
Chris
jayhawk
Strong Ale
Strong Ale
 
Posts: 472
Joined: Tue Dec 25, 2001 1:05 am
Location: Vancouver, BC, CA

good pun

Postby Gravity Thrills » Wed Nov 06, 2002 5:55 am

"attenuating circumstances..." I like that.

Yes you can calibrate a thermometer, by doing exactly as you are doing - check it against a known accurate thermometer or against physical constants like the boiling/freezing points of water at sea level. You want to do a double calibration, meaning check the suspect thermometer against one or more trusted thermometers at 2 different temps. Of course, the question is always what thermometer do you trust as "good"? Basically, the best you can do at home is to go with one that reads 100C at the time pure water starts to boil.

However, you may have a calibration issue with your hydrometer as well. here in the Sunny South I take my gravity readings at room temp, which is a balmy 80F (27C) most of the year. At this temp, hydrometers read 2-3 points low because they are usually calibrated to read true at 60F (15.6C). Even if your room temp is only 70F (21C), your hydrometer will still be reading 2 points too low. If your hydrometer is also reading off a couple of points, your 1005 may actually be 1009. Again, you have to calibrate against a trusted hydrometer (probably no such thing for the cheap dealies us homebrewers use) and/or against the readings of pure water with various known qiantities of dissolved solute (you could use table salt or sugar).

If you raelly find you are getting over-attenuation, then mash at a higher temp to obtain a mour unfermentable dextrinou wort, or you might add a a pound of dextrine malt.

Cheers,
jim
Gravity Thrills
Strong Ale
Strong Ale
 
Posts: 285
Joined: Thu Oct 25, 2001 10:12 pm

Here's the scoop.

Postby Brewer2001 » Wed Nov 06, 2002 8:37 pm

Chris,

Your thermometer is probably correct. Your mash temperature of 67C is the key to your lower attenuation. (I posted a message concerning this a while back.) The "brewers window" for infusion mashing is 63C to 70C and you are mashing at the lower end. Temperature and mash thickness (L/G ratio) both contribute toward fermentability. Cooler = more fermentable due to Beta-amylase action.
Warmer = less fermentable due to Alpha-amylase action.

Thicker mash (1/1 - 2/1) = more fermentable due to Beta-amylase action.
Thinner mash (3.5/1 - 4/1) = less fermentable due to Alpha-amylase action.

Another thing is that your yeast is in prime condition ready to work, provided the viability is good (it should be). I normaly have attenuation readings down at 1.005 with both my Irish Ale and Chico yeasts (Irish 13th generation, Chico 4th generation).

So,if you pitch this yeast again plan on adjusting the grain bill (maybe add some dextrin), mash temperature and mash thickness to work toward your desired result. This is the "ART" of infusion mashing. I have discovered that it was easier to hold a mash temperature when mashing more grain, just do to the added mass.

Good luck and good brewing,

Tom F.

P.S. I don't have a chiller (I'm a bad boy) and havn't had any problems to date. I do most of my brewing in the winter (Seattle is cool but mild...I did not say that!).
Brewer2001
Double IPA
Double IPA
 
Posts: 170
Joined: Fri Sep 07, 2001 1:56 am

Close by

Postby jayhawk » Wed Nov 06, 2002 9:12 pm

I am just north of you, just outside Vancouver BC. Thanks for the info, I will adjust as necessary.

I think part of the "problem" is that the yeast is, like you say, in prime condition. I am using a fresh German Ale wyeast on another batch, and it is very slow. I had the same thing happen with American Ale wyeast, the first gen was slow, the second was extremely fast. If I pitch a new batch on to the German ale yeast, I predict a much faster fermentation. Anyway thanks again for the mash info.
Chris
jayhawk
Strong Ale
Strong Ale
 
Posts: 472
Joined: Tue Dec 25, 2001 1:05 am
Location: Vancouver, BC, CA


Return to Brewing Science

Who is online

Users browsing this forum: No registered users and 1 guest