Partial Mash Question - mash temperature too high, low O.G.?

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KSR

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Long-time lurker, first-time poster here.

I started brewing PM batches a few months back after brewing extract for over a year, the first two batches were kits from AHS and they came out great. Once I felt that I had the technique pretty much down I started playing around with formulating my own recipes and riffing on others using BeerSmith. All of those came out right on target as well. However, I picked up two more AHS kits for my most recent brews and I've run into issues with the O.G. coming in around .008-.010 lower than expected in both batches.

While mulling it over in the shower this morning, I realized that I'd followed AHS's instructions to the letter in both of those batches EXCEPT for the mash temperature: I'd gotten used to heating X qts. of water to 168 as per BeerSmith's mash calculations for my custom recipes. AHS's PM recipes call for heating 2.5 gal. to 160F and holding the mash at 155. So what did I do? I heated 2.5 gallons to 168 out of habit and mashed 3lb. 2 oz. of grain in it for 60 minutes. Because I'd gotten overconfident I neglected to take a mash temperature reading, but I ran the numbers through BeerSmith and according to it, that resulted in a mash temp of 161. I did do a starch conversion test with both batches and the results told me that everything had converted, i.e. the iodine didn't turn purple or black.

I didn't worry about any of this with the first batch batch that was off, but now it looks like something's up.

I'm certain that this isn't just an issue of the extract not mixing with the top-off water. I'm a big guy and have no problems thoroughly shaking the fermenter for 5+ minutes, and I've never had any problems with mixing in my previous 30-some batches.

The expected O.G. for the last batch was 1.052, reading came in at 1.044. The grain bill is 10oz. c-20l, 2lb 2-row pale malt, and 5lb extra pale liquid extract.

Sorry about the long exposition, my question is this: could mashing at a higher temperature account for a nearly .010 difference in my O.G. even though the iodine test told me that conversion was complete? At this point I feel like it's either that or my hydrometer is wrong. Thanks.
 
What temperature was your wort when you took the hydrometer reading? Have you tested it in plain water?

You could try lowering your mash water volume a little bit and performing a mini sparge. That will help you get those ever so important sugars left behind in the grain.

The high mash temp can be the culprit for low extraction, but it doesnt sound like it in your case since you did the conversion test.
 
It was at 68 when I took the reading, so even after correcting for temperature it was pretty far off. I tested the hydrometer in 70 tap water today and it read 1.002 (uncorrected), which struck me as odd but I know that it's supposed to be tested in distilled water so I'll need to try that too.

Could you explain what you mean by mini sparge? I always put the grain bag into a colander over the pot and pour 170F water over the grain after the mash is finished. Is that the same thing?

I guess the thing to do is to go buy a different hydrometer and compare readings from the two to determine if that's the culprit.
 
...and mashed 3lb. 2 oz. of grain in it for 60 minutes
The grain bill is 10oz. c-20l, 2lb 2-row pale malt, and 5lb extra pale liquid extract

It looks to me like you mashed 2 lb. 10 oz. into 168 F. water, unless I missed something. Was there another grain? Because I think that 1.052 is optimistic with that grain bill. You'd have to top 90% efficiency which is unlikely in the best of circumstances.

Also, a higher temperature can mess with your efficiency. But it looks like you are getting ~50% efficiency from your PM, which isn't great, but considering you don't really sparge it's not awful.

If you want to bump your efficiency you could heat up a second pot of water to 170 F and transfer your grain bag to that for 5-10 min to extract more of the sugars. Just pouring hot water through the grains won't extract very much sugar.

They main thing to worry about with a high mash temperature is getting a lot of unfermentable sugars and bad attenuation as a result.
 
Oops, sorry. That should have read 2.5 lb. 2-row pale malt.

I'll try the heating up a pot next time around and see how it goes.
 
I read somewhere that if you mash at a higher temperature, you get sweeter, less fermentable wort and if you mash at a lower temperature, you get a dryer, thinner bodied beer. The higher temp was said to be 158° or higher and the lower temp was said to be at or below 150°.
 
I read somewhere that if you mash at a higher temperature, you get sweeter, less fermentable wort and if you mash at a lower temperature, you get a dryer, thinner bodied beer. The higher temp was said to be 158° or higher and the lower temp was said to be at or below 150°.

Yes, that is accurate in general; however, there are other factors which can also have an effect. If you are partial mashing, the fermentability of your extract will play an enourmous role in the final gravity/body of your beer.
 
Just to follow up, I ended up buying a 5 gal cooler with a false bottom and have been using that to make "big" partial mashes (20 - 30% of the fermentables are coming from extract, the rest from grain), and have been consistently getting 75 - 78% efficiencies while doing batch sparges with that setup. So, I think the problem definitely came down to poor mash temp control on my part and insufficient sparging when using the brew in a bag method.
 
A higher mash temp won't affect OG as long as you are waiting for starch->sugar conversion to happen.

You can get a higher or lower final gravity depending on the mash temp because you have different sugars produced in the tun, but a fully converted mash at 148 and a fully converted mash at 158 should have the same OG.
 
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