Author Topic: Gravity readings  (Read 19560 times)

Offline brewfun

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Re: Gravity readings
« Reply #15 on: December 01, 2013, 06:56:36 PM »
All that effort payin' off?
I measure pre/post boil only. Losing interest in that because it's becoming more predictable and I don't make adjustments anyways.

Tom doesn't need me to speak for him, but what he's outlined is a series of control points that ensure true predictability in the balance of the finished beer. That's a very professional methodology.

My reading schedule is irrelevant for this thread, but we measure during recirculation looking for a peak starting gravity (22 to 26 Plato, usually). Then at several points during the sparge, especially once we're under 5 Plato (about 1.020) because it drops one degree for each barrel.

Yet, we've been caught by surprise and gotten all of our sugar out long before sparge is finished. Without similar control points like Tom outlined, we'd have oversparged and come in way under gravity. That's especially problematic because a normal sparge gives us 92 to 95% mash efficiency.

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Offline MaltLicker

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Re: Gravity readings
« Reply #16 on: December 01, 2013, 07:05:36 PM »
we'd have oversparged and come in way under gravity. That's especially problematic because a normal sparge gives us 92 to 95% mash efficiency.

That's a whole new topic that might benefit new brewers.  OVER-sparging that reduces the gravity.  Many don't understand the dilution that occurs toward the end of sparging. 

Offline tom_hampton

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Re: Gravity readings
« Reply #17 on: December 02, 2013, 11:25:43 AM »
All that effort payin' off?


I measure pre/post boil only. Losing interest in that because it's becoming more predictable and I don't make adjustments anyways.

In short, yes.  Its a bit of a long explanation as to HOW...but, if people are interested I can compose a series of replies explaining how I use the readings to CONTROL my processes.  I don't just take the readings for fun.  I DO actually manipulate the process throughout the brewday (and fermentation) to ensure that I end up with the beer I expected to make. 

I manage the mash, the sparge, the boil, and the ferment via these readings.  I have procedures for tweaking each of these steps based on the readings that I take.  I'm happy to elaborate, if people are so inclined.
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Offline ihikeut

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Re: Gravity readings
« Reply #18 on: December 02, 2013, 12:30:25 PM »
I have to say welcome back Tom to.

I would definitely like  you to elaborate on the subject. Always more to learn about brewing.

Offline Slurk

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Re: Gravity readings
« Reply #19 on: December 02, 2013, 12:41:21 PM »

In short, yes.  Its a bit of a long explanation as to HOW...but, if people are interested I can compose a series of replies explaining how I use the readings to CONTROL my processes.

Hi Tom, nice to see you active again on the BS-forum!
I would like to improve my process control/reproducibility and I am interested to learn how you use your readings to control your processes. I am also interested in when and especially how you take your readings. I've seen some examples on the BS-forum where colleague members think they take the same readings or measurements, but they experience different results because they did it in a different way. Related to this perhaps some practical tips "what to avoid".
I am sure other members are interested as well.
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Offline tom_hampton

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Re: Gravity readings
« Reply #20 on: December 02, 2013, 08:52:29 PM »
Ok, lets see how far I get. 


total Points
------------

The diatribe below relies on the reader understanding the concept of gravity units or points.  Gravity units is simply the difference between the SG of wort and water.  So,

Points = 1000 x (SG - 1.0)

Lexically, simply remove the "1." from the 1.0xx = 0xx.  Eg. SG = 1.052 => points = 52

Total points is a measure of the total amount of sugar in the wort: points * volume.  For example:

Wort = 5.25 gallons @ 1.067 SG

5.25 * 67 = 351.75 points


I can convert points and volumes back and forth to SG at different volumes, by reversing the math:

I have 351.75 points, and I have a target SG of 1.075.  Simply, divide the total points by the target points.  Eg:

351.75 / 75 = 4.69 gallons.

I can also calculate the SG, if I have a desired volume, by dividing total points by the volume. Eg:

351.75 / 4 gallons = 87.94 points.  Close enough to 088.  Add the "1." to the front: 1.088 SG.


This math is extremely handy for determining what adjustment needs to be made to get from the amount of sugar and wort that I have to the desired SG. 

If I've done a poor job of explaining this, read John Palmer's book, "How to Brew".  I'm not inventing anything new here.

Mash
-------

The whole goal of the mash is to produce sweet wort with the desired volume and gravity.  Second, is the desired degree of fermentability and so-called "body". 

I've already described my method for managing mash temperature on the forum.  So, I won't repeat that here.  This is specifically about managing the gravity of (or, at least the total points in) the final wort pre-boil. 

A note about my sparging method: some of the below is partly specific to my method of sparging.  However, it can be allied to other methods, but there will be some changes necessary for deviations from my method.  I sparge in two equal batches: 4.04 gallons (at mash temp, or about 3.9 gallons at room temp). 

I calculate my strike water volume as grain_absorbtion + 4.04 gallons (again measured at mash temp).  Thus my expected runoff is 4.04 gallons (+/- any variation in absorbtion).  The more saavy of you may note that this implies a variable mash-thickness.  YES, you are correct.  In fact, you may also note that this is also fairly thin mash (close to 2.0 qt/lb for most regular 1050 beers).  However, I have not found this to have a measureable impact on my consistency.   Quite the opposite.  When I always held a 1.25 qt/lb mash thickness, my efficiency was all over the map from one brew to the next.  Once I switch to a fixed sparge volume, my results stabilized quite nicely.  YMMV.

From my reading of the literature mash thickness accounts for about 0.1 plato (2 sg) variation in FG from 0.9 qt/lb to 2.0 qt/lb.  My thickness varies from about 2.25 to 1.55, and my actual FG is generally within 1 sg of planned (frankly that is within measurement error).  The level of variation is more than dominated by mash temperature variation.  If a recipe ended low or high by 2 points, I would simply adjust the next itertion by 2F to compensate (assuming that I felt that the 2 sg was perceptible). 

So, sparging with 2 equal volumes means that approximately 2/3rd of my extract is going to be in my first runnings, and 1/3rd in my second batch runnings.  There are formlas for other numbers of batches, I can find them...but, I don't have them handy.  Further, you can do a similar set of math for fly-sparging, but that begins to look a lot like first-year calculus (not that there is anything wrong with that).  I use my method because its easy, predictable, and repeatable.  Why work harder than, I need to?

I try to keep my efficiency down around 70%, 65 - 75 is okay.  But, if I get can see that I'm going to be over 75%, I'll discard later wort, and replace with water.  Its a quality thing.  The lower the gravity of the wort, the less pH buffering power, and the faster the pH will rise during the sparge.  This begins to extract tannins and degrades the overall flavor of the wort.  this is not a huge concern with batch sparging.  Particularly when you keep the number of batches to two or three.  But, the more batches, the higher the risk and the more low qality wort is being added to the boil. 

A final note on recipe formulation:  I always formulate my recipes based on an efficiency that is 5% lower than typical.  This generally assures that I will always have excess extract from the mash.  I don't like to use DME to adjust upwards.  I think its just a hastle to store, and it gets all clumpy in the humid south....its just not much fun to work with to me.  So, I ensure I won't need it. 

This is a fairly classic approach that I use throughout my brewing processes.  If there is some variation, then I force an error in a direction that is easy for me to manipulate, so that I don't ever have to deal with the alternative. 

Ok, enough preamble: on with how I manage the mash....


Measurement methodology 
----------------------------------
I use a ATC optical refractometer.  I calibrate it with distilled water before every brew (along with my pH meter- 2 point cal, and my digital thermometer - 2 point cal).  Normally this is just a verification, because it hardly every needs to be corrected...maybe twice in the last two years. 

I take my sample by:

1.  Thoroughly stir the mash.  Ensure that the bottom is brought to the top and carefully look for any evidence of balling.
2.  Use a fine sieve pressed into the surface of the mash, 1/3rd of the way between the center and the edge of the Tun. 
3.  Use a turkey baster to draw a sample from within the sieve, and deposit into a heat proof vessel.  I use 50 ml auo-clavable test-tubes.
4.  Cap the tube, and drop in an ice bath for 30 seconds to cool.

Yes, my Refract is ATC, but evaporation of the drops (at near boiling temps) can skew the results high in the few seconds it takes to close the lid.  So, 30 seconds to cool into the low 100s improves my repeatability.  Besides it puts less reliance on the ATC which is always a good thing.

5.  Use an eye dropper or pipet to draw in a small sample from the test tube.  Flush and repeat 3-4 times to ensure that any previous sample doesn't skew my new sample.
6.  Flood the surface of the refract with the sample, both the lid and the glass.  Close glass immediately, ensuring that no air is trapped.
7.  Use bright light to illuminate refract, and interpolate the boundary between "white" and "blue".
8.  Return larger sample to ice bath and continue to cool to room temp (~25 C).
9.  Take pH measurement of cooled sample.

pH Measurement:
---------------------
1.  Clean probe in distilled water.
2.  Shake excess water off of probe and insert into sample. 
3.  Slowly stir sample with probe---use circles and up and down motions to ensure sample remains mixed and no local pH minima or maxima develops. 
4.  Allow probe to sit in sample for 30 - 60 seconds, until reading stabilizes.
5.  Repeat stirring from step 3 and 4 until reading doesn't change.
6.  Record reading.
7.  Remove probe and rinse in tap water.
8.  Return probe to distilled water. 

Temp Measurement:
-------------------------
NOTE: Its best to take mash temp measurements after stirring.  However, stirring can cause a lot of heat to be lost for a typical 5 gallon batch.  So, I don't stir for intermediate measurements.  However, if I'm stirring anyway (eg: after adjusting pH, or taking a ph/gravity sample) I always take a temp measurement while the temperature is nice and uniform.

1.  Insert probe in center of mash.
2.  Allow probe reading to stabilize (depends on thermo..mine is a needle / thermocouple and stabilizes in 2 seconds).
3.  Slowly move probe from one side of mash to the other.  Note any variation.  If not, record "average" reading.
4.  If there is more than 2 degrees of variation from middle to edge, then take 3 measurements and average result (middle, 1/2 way, 1 inch from edge).


Mash SG Correction
------------------------
As noted above by Brewfun, the SG of the mash will increase with time as AA and BA work on the starches and convert them to sugars.  This process continues long after "starch conversion" is complete as measured by an iodine test.  Depending on the rest temperature, and other mash conditions this can progress well into the 90 - 120 minute time frame.  So, about 75% of though way through my sach-rest I take a gravity measurement.  I always take pH and Temp while I'm in there to minimize the amount of heat lost.


Generally, at the 75% point I'll still be a few points low.  However, it tells me where I'm at.  If I'm still off by 1 plato, I may need another 30 minutes (eg, and extra 15 minutes beyond my normal 60 minute mash).  If I'm within 1/2 plato, then 60 minutes should be dead-on.  If I'm already at my desired SG, then its time to drain and start the next batch.  I find that 15 minutes per 1/2 plato (2 sg) is a good rule of thumb, towards the end of the mash.  I continue to take measurments every 15 minutes until I reach my target SG, or the readings stop improving.  As I said above, I always underestimate my efficiency, so I really never have to deal with not reaching my target SG. 

YMMV---take a few measurements and you will quickly see what yours looks like.  it will vary with temperature range, as well.  Generally hotter will progress faster (to a point) but will reach its terminal point sooner, and cooler will progress slower but will usually reach a higher terminal point (all other things being equal).

All of the above is a long way around to the following procedure:

1.  Mash-in
2.  At 45 minutes (or 75% of mash duration if not 60 minutes) measure SG.
3.  For every 2 points low expect 15 additional miniutes for the mash.
4.  Take additional SG measurements every 15 minutes.  Adjust expected duration based on actual points gained.
5.  Once desired FG is achieved, initiate the sparge.


Once I've drained all the wort into the kettle, I take a volume, SG, and temp measurement.  At the same time, I begin refilling the MLT with my next sparge addition (4.04 gallons of 180F water).  I then correct my first runnings volume (divide by 1.04) and calculate the actual total SG points collected.  Typically, I will be 1-2 SG higher because conversion and dissolution will continue during recirculation. 

If my volume is dead on, I will have a small excess of points from my first batch.  This means that I won't need all of my second batch sparge.  If my volume is a little low, then I'm probably dead on.

Once I know how many points I accumulated in my first sparge, I can calculate how many points I need from my second sparge.  Once the MLT is full with the sparge water, I can take another gravity measurement and calculate how much volume will be required from the second runnings in order to obtain my total points. 

Again, the procedure is:

1.  Calculate total points in first batch sparge: batch1_total_points = volume (room temp) * batch_points
2.  Calculate points needed from second batch: batch2_needed_total_points = total_points - batch1_total_points
3.  Measure the SG of the batch2 mash.
4.  Calculate the volume needed from batch2: batch2_needed_volume = batch2_needed_total_points / batch2_points
5.  Drain that volume into your kettle.

Now, I have a volume of wort in my kettle with exactly the right amount of sugar in it, but the volume may be high or low.  Most likely it is dead on, or low by less than a quart.  if it is low, you can either top up with water, or you can just shorten the boil by the appropriate amount.  I'm usually off by 2 cups or less.  On most systems that's about 7 minutes of boil time.  For that, I don't bother to top up. 

If I'm off by a quart, then I top up.  I don't want my boil time to be too much shorter or flavors that develop during the boil won't be the same between batches.  But, 8-10 minutes won't make that much difference.


At this point, in most cases I have wort in the kettle that is ready to boil.  Its the right amount of wort at the right SG.  I did say "most cases".  So, what about those?


Problem solving
---------------

There are some other possibilities:

1.  I could have too much wort.  Maybe I was lazy and didn't feel like calculating the amount of needed run-off from batch2, and my efficientcy was higher than expected.  Maybe my first runnings came up short on volume, and I added extra water to my second runnings...and it ALL drained out in the second runnings.  Now I've got an extra 1/2 gallon of nice sweet wort. 

2. Maybe despite your best efforts your efficiency still came up short?  It happens.  Maybe the mill was on the wrong setting or the rollers are old, or its just a goofy batch of malt from a different supplier.  Now what?  You've got the right amount of wort, but its short by 50 points. 

3. Maybe Absorption was off, and you don't have enough wort...and efficiency was low.  So, I don't have enough wort, and its not sugary enough.  These are the days that just pi$$ you off.

I suppose there are other possibilities, but honestly these are really rare for me these days.  Further, if you've gotten this far and understand the solutions to #1, #2, and #3...you should be able to solve any other variation that comes along.


Too much wort
------------

There are two options:

1.  Remove the correct amount of excecss wort, and correct the volume back to the expected pre-boil volume.
2.  Make extra beer.

#1 is a good exercise in how to use the total points math, but honestly that's just throwing away beer!  Anyway, just for fun...here's how you would do it:

1.  Calculate total points in the kettle (total_kettle_points).
2.  Calculate the number of points to be removed (excess_points).
3.  Measure the SG in the kettle (kettle_SG)
4.  Calculate the volume to be removed (excess_points - kettle_SG).

NOTE: this is ROOM TEMPERATURE volume. 

5.  Correct for kettle temp: 1.04 * room_temp_volume = removed volume (you can use 1.03 if you are still closer to mash temp)
6.  Add water to adjust back to desired preboil volume.


#2 make more beer - Duh!

1.  Calculate total points in the kettle (total_kettle_points).
2.  Determine desired final volume: total_kettel_points / (postboil_Target_SG_points)
3.  Correct for temperature (*1.04) = boil_down_to_volume
4.  Determine boil duration: (total_kettle_volume - boil_down_to_volume) / boiloff_rate
5.  Add water as needed to increate boil duration for planned duration: duration_increase * boiloff_rate

NOTE: now that you changed your boil volumes and final batch size, you need to adjust your hops accordingly.
6.  Adjust hop additions to match new volumes. 


Poor Efficiency
---------------
Again, two options:

1.  Add DME to make up the points.
2.  Make less beer.

No one wants to make less beer, but as I said above I don't keep DME on-hand.  So, I don't have much choice if this happens, that's why I take the extra care to try and ensure that it does not.

#1 DME adds ~45 points per pound.

1.  Calculate total points in the kettle (total_kettle_points).
2.  Calculate how many points the kettle is low (points_low).
3.  Calculate needed DME: points_low / 45 points per pound.
4.  Add DME.

#2  Make Less beer (exactly the same as the make more beer option above)
1.  Calculate total points in the kettle (total_kettle_points).
2.  Determine desired final volume: total_kettel_points / (postboil_Target_SG_points)
3.  Correct for temperature (*1.04) = boil_down_to_volume
4.  Determine boil duration: (total_kettle_volume - boil_down_to_volume) / boiloff_rate
5.  Add water as needed to increate boil duration for planned duration: duration_increase * boiloff_rate

NOTE: now that you changed your boil volumes and final batch size, you need to adjust your hops accordingly.
6.  Adjust hop additions to match new volumes. 

Low volume & Poor efficiency
---------------------------

Just quit and go watch football.  :-)  That's certainly how I felt.  Anyway, its the same as the poor efficiency above, with one exception: For #1 (add DME), I will also need to add water to get my volume up. 


Ok...enough of that.  The above should show you the power of the total points method. It should also highlight the utility of a refractometer.  Cooling all the samples isn't much fun for a hydrometer.  But, you HAVE to in order to get accurate readings.  No hydr sample should ever be above 90F.  The correction tables just don't work well above that (or the hydro doesn't or both...anyway the readings will vary wildly). 

the length of this post can make it seem like this is really, really complicated.  But, in reality it is not.  In practice, it all comes down to two things:

1.  Calculate your recipe assuming 5% less efficiency that you normally get.
2.  Measure the gravity of the mash, and don't sparge the first batch until its gravity equals your desired gravity.

1.  Mash-in
2.  At 45 minutes (or 75% of mash duration if not 60 minutes) measure SG.
3.  For every 2 points low expect 15 additional miniutes for the mash.
4.  Take additional SG measurements every 15 minutes.  Adjust expected duration based on actual points gained.
5.  Once desired FG is achieved, initiate the sparge.
6.  Fill mash tun with water for second batch.
7.  Calculate total points in first batch sparge: batch1_total_points = volume (room temp) * batch_points
8.  Calculate points needed from second batch: batch2_needed_total_points = total_points - batch1_total_points
9.  Measure the SG of the batch2 mash.
10.  Calculate the volume needed from batch2: batch2_needed_volume = batch2_needed_total_points / batch2_points
11.  Drain that volume into your kettle.

In reality, at step 7...in almost all cases I'm dead-on my predictions.  In that case, steps 8, and 10 are skipped, and I just drain the mash tun.  And get on with the boil.





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Offline philm63

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Re: Gravity readings
« Reply #21 on: December 03, 2013, 04:51:39 AM »
@ Tom - First; it's good to see you back in the saddle. Second; wow! Now THAT's the Tom we all know and love.

Many of your control points may seem excessive for some, but for me; these may just be the points I was missing! My first several batches of all-grain were not telling of what was ahead - I was hitting all my numbers and coming up with some nice beers early on, probably just dumb luck.

But for some reason (not paying attention to control points) my efficiency has since tanked and I'm missing several targets during the brew day. This info should help me get back on track - just what the doctor ordered - thanks!
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Offline brewfun

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Re: Gravity readings
« Reply #22 on: December 03, 2013, 11:41:03 AM »
The above should show you the power of the total points method. It should also highlight the utility of a refractometer.

Excellent!

The mash is one place where we standardize all of our beers. They all get the same liquor ratio, same rest temp, same timing. It lets me build flavor through ingredients and fermentation.

I think every brewer should have a part of their process that they don't vary. Predictability is the brewer's friend. The mash is an excellent place to start.
Beer Appreciation is the space between pints.

Offline Scott Ickes

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Re: Gravity readings
« Reply #23 on: December 03, 2013, 11:45:28 AM »
In my humble opinion, Tom's thesis should be a sticky of it's own someplace.

Excellent work Tom!  +1
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Offline ihikeut

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Re: Gravity readings
« Reply #24 on: December 03, 2013, 12:52:47 PM »
Tom's back
 +1 Excellent

Offline durrettd

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Re: Gravity readings
« Reply #25 on: December 03, 2013, 01:06:26 PM »
Tom, Thank you for the excellent explanation! We've missed your input. This post needs to be pinned or otherwise made readily accessible to all brewers.

It's worth noting that both Tom's intensive measurement and granthan's     I take what I get because I've been doing this long enough to know what I'll get     approaches are both valid ways to brew. The two approaches pretty well define the spectrum of brewing approaches. I split the difference between the two ends of the spectrum and live with occasional pleasant/unpleasant surprises.

GReat thread!

Offline tom_hampton

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Re: Gravity readings
« Reply #26 on: December 03, 2013, 04:19:57 PM »
Tom, Thank you for the excellent explanation! We've missed your input. This post needs to be pinned or otherwise made readily accessible to all brewers.

It's worth noting that both Tom's intensive measurement and granthan's     I take what I get because I've been doing this long enough to know what I'll get     approaches are both valid ways to brew. The two approaches pretty well define the spectrum of brewing approaches. I split the difference between the two ends of the spectrum and live with occasional pleasant/unpleasant surprises.

GReat thread!

Absolutely!  I wouldn't disagree in the slightest.  I DECIDE before every brew, what degree of rigor I'm going apply to the brew session.  Heck, I've gone totally "open loop" many times: eg, just mixing water and grain, setting the watch, and not taking a single measurement.   The beer comes out "fine".  That's usually out of necessity, though...eg: because my hydrometer died, my thermometer won't calibrate, or some other "issue". 

Besides, as I said above...most of the time I have very little or no corrections to make.  But, I KNOW before I ever open the valve on the MLT that the current session is exactly on track.  Typical variation is +/-2 sg, and +/- 1/2 quart.
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Aging/Storing: Coffee Porter, Chocolate Porter, Flanders Red, English Barlywine
Fermenting: Maggie's Altbier
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Offline tom_hampton

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Re: Gravity readings
« Reply #27 on: December 03, 2013, 04:53:52 PM »
For those interested in the data that supports the mash_duration effect on original extract (and the limited effect on FG), here is a nice measurement study done by Kai. 

http://braukaiser.com/wiki/index.php?title=Mash_Time_Dependency_of_Wort_Fermentability

Note that SG continues to increase out to approx 1:45, and FG doesn't begin to drop until after the 2 hour mark. These times shouldn't be taken as absolutes, but rather the shape of the curve is the key.  OG will continue to increase, then plateau...then decrease.  The decrease will also be followed by a dropping FG, neither of these changes are good for the final beer.  So, Once the SG of the mash plateaus....you're done, and should sparge and heat the runnings to a boil, so as to halt further enzymatic activity. 

In the famous words of Mr. Scott:

"I'm giving her all she's got Captain!"


Also note that the OG increases by 20% (from 10.75 P to 13 P) from 40 minutes to 1:40 minutes.   That's 1.042 to 1.052 in an hour.  That is a LOT of variation in extract efficiency.   
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Offline grathan

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Re: Gravity readings
« Reply #28 on: December 03, 2013, 05:34:11 PM »
Hey good stuff Tom. Just wondering..

Can you taste the difference in 2 starting gravity points in the finished beer? I mean if your OG was 1.050 and your target recipe was 1.048 would you know? I know you don't get a lot of practice at comparing now if you use your method every time, but perhaps this is something that caused this type of deliberate methods?

Also, If you mash for an extra 15 minutes (I know you said your mashing methods were discussed on the forum, but I don't see them atm) are you concerned about dextrins being broken down into simple sugars? thanks

Offline tom_hampton

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Re: Gravity readings
« Reply #29 on: December 03, 2013, 05:58:59 PM »
Hey good stuff Tom. Just wondering..

Can you taste the difference in 2 starting gravity points in the finished beer? I mean if your OG was 1.050 and your target recipe was 1.048 would you know? I know you don't get a lot of practice at comparing now if you use your method every time, but perhaps this is something that caused this type of deliberate methods?

Honestly? No, I can't.  4?....Maybe  More than 4?...definitely.  The point is to control the process to some level below the perception threshold of the intended audience.   Any brewer can choose that threshold according to their own standards. 


Also, If you mash for an extra 15 minutes (I know you said your mashing methods were discussed on the forum, but I don't see them atm) are you concerned about dextrins being broken down into simple sugars? thanks

No.  The data I just presented above (from Kai T.) doesn't support it.  Nor does my own.  As long as you don't mash long enough for the OG to begin to FALL, FG of the final beer is determined by the Mash temp, ONLY. 

FG of the fermented wort does not change until well after OG has plateaued.

My theory (without any data) would be that dextrins are being created as quickly as they are being decomposed from the 0:40 mark out to the 1:40 mark.  At that point, all larger chain molecules have been exhausted.  At that point, dextrin conversion continues into more and more simple sugars, ultimately depleting the dextrin supply at which point the wort is almost completely simple sugars.  Once the medium chain starches are depleted, and the dextrin supply starts to decrease the ultimate FG is going to begin to fall, within the limits of the yeast attenuation.   



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