Questions Regarding Yeast Pitching and Boil Duration

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Questions Regarding Yeast Pitching and Boil Duration

Postby scorriga » Sun Aug 14, 2005 7:55 pm

My friend and I just tasted the fruits of our first effort at home brewing. We made an English Pale Ale and all things considered, it came out well. I have a few questions about things we did and how they may have affected the final outcome.

First, we forgot to check the OG until after we had pitched the yeast. Since we did not have a seperate vile, we checked it directly in the primary after carefully sanitizing the hydrometer. My first question is this: is one supposed to check the OG prior to pitching the yeast for the sake of sanitation and not removing any yeast from the primary, or is it because the addition of the yeast can actually affect the OG reading?

Second, the beer we ended up with certainly does not taste bad but it lacks a bit of flavor given the type of beer it is. It's very mellow (almost like a wheat beer). One mistake we did make while cooking the wort is we forgot to add the malt powder (not extract) that was supplied with our kit. Having realized this when we were ~40 minutes into our 60 minute boil, we added the powder and boiled for another 60 minutes for a total of about 100 minutes. At the time we thought this would be better than leaving out the malt powder altogther or short-boiling after it was added, but i'm wondering if some of the lack of bitterness and flavor in the final product could be a result of the prolonged boil.

Any insight that can be offered relative the the reason behind measuring OG prior to pitching the yeast, or the effects that a prolonged boil could have on flavor would be much appreciated.

Regards.
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Postby BillyBock » Sun Aug 14, 2005 11:40 pm

Congrats on your first brew!

It's best to check the OG before pitching the yeast as they can affect the reading if they begin fermenting.

If you post the recipe, we might be able to help you out. What kind of flavor do you think it was missing? Not enough malt? Not enough hop flavor? Not enough bitterness? Etc.
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Questions Regarding Yeast Pitching and Boil Duration

Postby scorriga » Mon Aug 15, 2005 12:49 am

Thanks for the response. The recipe was a Brewer's Best kit, and included the following ingredients:

8.0 oz Crushed Crystal Malt 60L
3.3 lbs Plain Light Malt Extract (Munton's)
2.0 lbs Plain Light Dry Malt Extract
1.0 oz Perle Hops (Bittering)
1.5 oz Willamette Hops (Finishing)
Hop IBUs: 20-40
1 packet of Dried Yeast
5.0 oz Sugar (Priming)
Target OG: 1.044-1.048 (ours read 1.039)
Target FG: 1.012-1.015 (our read 1.008)

We did our boil using a full 5 gallons. We steeped the crushed crystal malt for 15 minutes at 165 F, then removed them and brought the pot to a boil. We then added the malt extract, brought back to a boil and added the bittering hops. Then, as I said, we realized after 40 or so minutes that we forgot to add the dry malt extract so we added that and boiled for another 55 minutes (total of 95 minutes rather than the 55 minutes specified in the recipe). At the 95 minute mark we added the finishing hops and boiled for another 5 minutes, then removed from heat and cooled the wort (which took us about an hour to get below 75 F). There were no other anomolies that we were aware of besides that we boiled longer than the 60 minutes total specified and it took us longer than the 30 minute target to cool the wort.

Regarding taste, maybe my expectations were skewed but I guess I was expecting a bit more bitterness (there is very very little) and perhaps a bit more hop flavor (again, there is very very little). I was thinking that maybe the prolonged boil after adding the bittering hops could have affected the final taste, but that's just an (un)educated guess! Thanks for your help!
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Postby BillyBock » Tue Aug 16, 2005 5:56 am

Your recipe should've had a target OG=1.045 @ 5 gals. Do you remember your volume when you took the reading? When did you take the reading: pre-boil or post-boil? The gravity will decrease with more liquid given the same amount of sugars. So in this case to get an OG=1.039 your post-boil volume would be about 5.7 gals. Another reason for an 'off' hydrometer reading is wort stratification in the boil kettle if you take the reading pre-boil. It has to be stirred up well, if not the heavier wort will sink.
Another reason is forgetting to adjust the hydrometer sample's reading for temperature. And just having read your original post, it's possible some of the wort fermented before you took the reading in the fermenter--was there much delay between the pitching of the yeast and the hydrometer sampling?

This recipe should've been relatively bitter given it's lower gravity. There were no flavor additions, so what little flavor there is was probably extracted from the aroma addition if you let it sit in the kettle during cooling. I've found this to happen in my beers, so I take the aroma addition out at the end of the boil.

As far as the late addition of the DME...I think you would've been fine just adding it and finishing up the last 20 minutes of your boil instead of boiling for an extra 60 minutes. Now if you'd have forgotten the hops that'd be different :D Hop extraction efficiency is dependant on wort gravity--but in this case it's minimal. So just cook the extract long enough to sterilize it and you'll be fine. Your wort probably came out darker than originally intended.

Hope this helps you out.

v/r
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Postby scorriga » Tue Aug 16, 2005 7:43 pm

We siphoned quietly from the boiling pot into the primary (after cooling), topped off with ~0.5 gallon to make 5 gallons, added the yeast and gently stirred it in, then took the OG reading immediately. Therefore, I don't think there would have been time for much/any fermentation to occur and I'm pretty confident that our mixing destratified the wort prior to the OG measurement.

However, as I think about your reply I recall having read that transferring some of the trub (which had largely precipitated out during cooling) is important for good yeast response. I suppose the amount of trub that is transferred into the primary would also affect the OG reading, correct? It seems that our quiet siphoning might not have been the correct way to transfer the wort into the fermenting vessel, but how does one know how much of the particulate matter to move from the boiling pot to the primary?

Thanks for the help!
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Postby BillyBock » Wed Aug 17, 2005 6:50 am

I've had occassions where I thought I mixed it up completely only to find out later that I didn't because the readings were skewed. I believe the half gallon of water you added (even though you stirred) was what threw your reading slightly off due to stratification. I've found the best time to take the reading is immediately after the boil--boiling is an excellent mixer. In your case it would've been 4.5 gals, but it would be easy enough to compute your gravity at 5 gals without actually taking the reading. There's no extract efficiencies to worry about using extract (like there is with all grain).

As far as trub, since I use a counterflow chiller I get maximum cold break in the fermenter all the time. I just don't worry about removing it. I've had times where I've had too much sediment in the hydrometer jar (yeast and/or trub) and it greatly affected the reading. Make sure you take as clear a sample as possible to avoid this happening.
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Postby scorriga » Sun Aug 21, 2005 7:54 pm

Thanks for the help. I would guess that to adjust the SG to allow for the added top-off water, one would just multiply the weight percent of the concentrated wort (relative to the final 5 gallon mixture) by the SG of the concentrated wort, then add the weight percent of the top off water (multiplied by the SG of the top off water, which of course is 1.0). Is this correct?
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Adjusting Specific Gravity After Adding Make-Up Water

Postby scorriga » Mon Aug 29, 2005 10:55 pm

I sorted this one out on my own, so I thought I'd post the answer. Per the above response, it's often best to measure SG after completing the boil but prior to adding make-up water to ensure that the results aren't skewed by stratification of the water and boiled wort. So, using an expansion of "mass/volume" normalized to the SG of water (1.0 g/cc), which is the definition of SG, one obtains:

SG_mixture=((SG_wort*Rho_water*V_wort)+(SG_water*Rho_water*V_water))/ (V_wort +V_water)

This can then be seperated as follows:

SG_mixture=(SG_wort*Rho_water)*(V_wort/(V_wort+V_water))+(SG_water*Rho_water)*(V_water/(V_wort+V_water))

It can be seen that this is simply the SG of the two solutions (wort concentrate and make-up water) weighted by their respective volume fractions in the final mixture and added together.
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Handy Ratio

Postby BillyBock » Tue Aug 30, 2005 5:44 am

My apologies for not answering sooner. Yes, you're correct. An alternate form of this equation can be found in Ray Daniels' book, "Designing Great Beers." Total gravity, TG, (defined as SG * Volume) is the same at the start of the boil as it is at the end of a boil (conservation of mass):

TG (start) = TG (End)
SG (start) * Volume (start) = SG (end) * Volume (end)

Rearranging:
SG (end) = [SG (start) * Volume (start)] / Volume (end)


An application:
You just got done with a boil and transferred to the fermenter, Vol=10 gal, SG=60. You want to add 2 gals of water to top off the fermenter to 12 gal. What's the gravity in the fermenter?

SG (end) = (60 * 10) / 12
SG (end) = 50 (ie. 1.050)

Another one:
You just collected 13 gals of wort pre-boil with an SG=40. You know your evaporation rate, so at the end of the boil you expect to have 11 gals. What should the gravity be post-boil?

SG (end) = (40 * 13) / 11
SG (end) = 47 (ie. 1.047)

It's a handy ratio I use all the time and works quite well regardless of whether you add water or evaporate water--since the amount of sugars in solution doesn't change, it's the volume of water that changes. In the long version of the formula the water factor 'drops out' and you're left with the short version.
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