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Old 03-08-2013, 03:00 PM   #1
BrewLocal365
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Default Missed my Mash Temp: What should I have done?

Long story short: My digital probe thermometer started giving unreliable readings about halfway through my mash, but I didn't realize it until I was sparging. I missed my pre-boil gravity by 11 points and my OG by 10 points.

I am sure it will still be a fine beer, but if I wanted to keep tight to the recipe, what would have been the best course of action, given that I didn't have any DME on hand (a mistake!)?

Should I have boiled it down until I reached the proper OG? If I had done that, how would I have adjusted the hop schedule? Should I have boiled it without hops until I hit the pre-boil gravity, and then followed the hop schedule per the recipe?

As an aside, I have been toying with the idea of getting a refractometer because I hate the process of cooling the wort to get decent readings. This is a situation where, if I wanted to make adjustments, it would have been invaluable. I never would have been able to get an accurate hydrometer reading in time to adjust the boil.


Long story long for anyone interested: The recipe was the Fat Tire AG clone from Norther Brewer. I've been experimenting lately and wanted to try a multi-step infusion (even though I know it's not necessary).

I decided to follow a three-step mash schedule, with the final step to mash out being a decoction. That's both because I was curious to see if the decoction made a difference to the recipe and I had no other way of doing a three-step due to my 5 gallon mash tun. Everything I've read says that the clone is good but not close to the real thing. I thought maybe the optional three-step schedule, with a decoction, might close that gap. After all, Fat Tire has a certain caramel character that decoction could help to bring out.

I was using two thermometers: a digital probe on my HLT (a large canning pot) and an analog dial-on-a-stick in my mash tun (5 gal cooler). Out of necessity, my first mash step was thick (0.8 qt/lb). It was able to hold and support the analog thermometer very easily.

Everything went great and I seemed to be hitting all my temperatures. I hit the first 122 degree step spot-on. For the second step I hit 154 instead of 152. Not perfect but OK. Here is where my temperature readings went a bit off the rails.

When I poured in that second (aiming for 152) infusion I forgot about the thermometer and poured straight over it. I tried to find it with my spoon but had no luck, so I just left it in (I found it by accident just before sparking, which is good because it probably would have messed with my grain bed). So I had to make my digital probe do double duty, moving it between the HLT and mash tun.

While sitting at the 152 step for 60 minutes I got my spare water up to 168 and turned off the heat. But the temp reading kept climbing. 180. 200. The probe was not against the side of the pot. I thought maybe moving it back and forth was causing some sort of lag on the reading. I should have been more skeptical, but instead I turned off the heat and started removing a quart at a time from the HLT and replacing it with cold water to get the temp down.

After adding the decoction, I moved the probe back to the mash tun, and got a reading over 200 degrees! This was while I was trying to bring down the temperature of the HLT. I left the lid off in an effort to get THAT temp down. This is about the point where I began to seriously suspect that my digital thermometer had gone wonky. Luckily, this is also about the moment when I accidentally scooped up the analog one.

Well, the HLT was actually at 100 degrees and the mash tun at 145. I covered the mash tun and put the heat back on the sparge water, which took about 20 minutes to get up to 168. Then I fly sparged as normal and got on with it.

Target pre-boil gravity was 1.045 and measured was 1.034. Target OG was 1.052 and measures was 1.042. BeerSmith tells me my efficiency was ~62%.

This may be a result of my thick initial mash step. After all, I more or less hit the target temperatures for the first two steps, and I *think* I hit the temperature for the mash-out (will never really know). Sure, the mash sat for an extra 20 minutes during mash-out at a low temperature, but that should have no effect, right? One other note: I grind at my LBS and in the past the grind their setup provides has always proven consistent and reliable, so I don't think the crush was an issue.

So two questions for those reading in detail:
  1. Do you think the efficiency was due to the mash thickness, the temperature issues, or both?
  2. Given my lack of DME, if I wanted to hit my targets, should I have boiled it down until I hit my pre-boil gravity (making a ~3.5 gallon instead of a 5 gallon batch), or something else?
  3. Anyone want to buy a 5 gallon MLT? I usually make smaller beers, so to-date this hasn't been a problem, but my next one is a double IPA, and given this experience I think it's time to uprade to a 10 gallon tank! When I bought my gear I didn't know the limits of a 5 gallon cooler in terms of bigger beers. If nothing else, I'll use it as my HLT to hold my sparge temperature and make fly sparging easier.

Thanks!
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Old 03-08-2013, 03:40 PM   #2
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1. Probably neither. You were at 152 ish. Then you monkeyed with it over a range of time and dropped the temp to 145. Anything in that range is going to convert. A typical commercial crush should be expected to yield something in the range of 70% efficiency on a decent brew day. If you were busy monkeying around with temps, it is pretty likely you got a little lax with the simple things (stirring well after the conversion water addition etc) and your efficiency suffered a bit.

2. If you could have caught the low OG early, you could have just increased your sparge water. eg add an extra gallon. Then you would boil down to your normal starting volume before starting your hop schedule. That way, you add you hops as usual and don't mess up bitterness etc.

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Old 03-08-2013, 03:56 PM   #3
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Thanks! You made me think of a point that I meant to make but forgot. My crush/grind is from my local store and it has always provided good efficiency in the past, so that's why it wasn't on my list of suspects.

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