A couple temp questions

So I just brewed my 4th batch (second all grain). My first question is regarding the mash temp. I mashed in a 42 qt cooler that was covered in blankets. The first time I was noticing the temp drop rapidly, but i was also having trouble with my thermometer so I assumed that was the big issue. This time I used rubber to significantly improve the seal around the cooler lid (its so tight now I have to pry it open). I wanted to aim for a temp of 154. I put the strike water (163 deg.) and let it sit for 5-10 min. to warm up the cooler. When I put the grains in, the temp went down to 151. I poured in some boiling water and the temp shot up to 157, but then went down to 154 in about 10 min. I was happy until i noticed the temp kept dropping steadily. At the end of the mash the temp was 149! My current thinking is that it is because I didn't preheat the cooler long enough. I saw one thread where someone recommended a 3 hour preheat. I would love to get more input on this. My efficiency was something terrible like 53%. Is this because of the temperature drop?

My next question has to do with fermentation temp. I put this batch in the fermentor in a room that was 68 degrees. I checked it the next morning and the sticky thermometer on the outside of my plastic carboy read 73. I decided to try something new, and I put a sanitized digital thermometer in the fermentor. It read 83! I quickly started cooling it down with a wet towel and a fan and cooling the room temp. I got it down to 75 and shut off the fan and let the room temp slowly rise back up (I left the towel on). The next day, the temp was 67! And fermentation seems to have stopped or significantly died down. So what should I have done, and how much did all this change in temp affect the beer?

I apologize for the long post, any help is greatly appreciated!

On the temp drop, I think it has to do with the poor quality of the cooler insulation. I don't do any pre-warming and my cooler drops only 2F in 1h. What ambient temp are you mashing in? This will also affect the temp drop.
Regarding the fermentation temp, temp will increase few degrees with an active fermentation. if you want to make sure to be looking at the beer temp and not the external wall of the fermenter, get one of those meat cooking digital thermometers with a external probe on a few feet of cable. You can get the probe in the beer thru a small hole on the top of your fermeter. These run pretty cheap, probably less than $20.

nilo said:

Regarding the fermentation temp, temp will increase few degrees with an active fermentation. if you want to make sure to be looking at the beer temp and not the external wall of the fermenter, get one of those meat cooking digital thermometers with a external probe on a few feet of cable. You can get the probe in the beer thru a small hole on the top of your fermeter. These run pretty cheap, probably less than $20.

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Thank you for the quick reply! I used a digital thermometer that I put right inside the fermentor and that's what read 83 degrees (15 degrees above room temp), and 10 degrees warmer than the thermometer on the outside of the fermentor.

just sayig you could leave one monitoring the temp continuously. I'm assuming you didn't leave your thermometer inside the fermenter. Some of these meat thermometers are wireless, you have one small box connected to the probe (transmitter) and another you take with you, so you can monitor the temp while you watch your TV or something. Some may also have high or low temp alarms you can set, so it would let you know if something is out of normal.

Yeah the thermometer I have is similar to what you are talking about. I was able to leave it in there.

Agree with Milo about your mash temp dropping is probably about your cooler - I use a cooler and don't lose much or any temp during the mash. Its a round cooler, Home Depot store brand.

Your fermentation temp dropping to 67 was unlikely to stop your yeast. I routinely ferment at five degrees or more cooler than that without problems. More likely, I think, was that your yeast activity was especially quick because of the early high temps.

Thank you for the replies! I'll have to look into getting another cooler.

Thank you for the replies! I'll have to look into getting another cooler.

154-149 deg F is fine for mash temps.
* How are you measuring efficiency?
* What is your ratio of water to grains in the mash? should be around 1.5-2.0qt/lb
* How does the crush look?

jCOSbrew said:

154-149 deg F is fine for mash temps.
* How are you measuring efficiency?
* What is your ratio of water to grains in the mash? should be around 1.5-2.0qt/lb
* How does the crush look?

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Is it really fine for the mash to drop 5 degrees?

I measured the preboil gravity and plugged it into beersmith to get the efficiency.

I used beersmith to calculate volumes of water. It was 13# of grain to 15qts of water,which sounds about right.

I crushed using my LHBS mill. I don't know what the crush should and shouldn't look like.

JeffD1 said:

Thank you for the replies! I'll have to look into getting another cooler.

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Make a test with the new cooler, some hot water at 170F, leave it for 1h and check before and after. If it drops just 2 to 3F, make all the building and such, otherwise, return it get another one. my 2c.

I've found that a stainless steel kettle holds the mash temperature better than a cooler. Plus with a kettle you get the advantage of being able to apply a little heat if needed rather than more hot water.

Cost is quite a bit more. I bought one of the kettles MoreBeer sells already tapped for a thermometer and ball valve for about $100. Add the valve, thermometer and manifold and its just under $175. But I see it as an investment in good tools. And now if I want to try stepped mashes I'm all ready to go.

jCOSbrew said:

154-149 deg F is fine for mash temps.

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Oh and BTW, a +1 to jCOSbrew on the mash temp.

In Palmer's book "How to Brew" he says to check the temp every 20 minutes or so and if it drops to 145F after a half hour to add hot water to bring it back up. If you are holding that close to 150 for the entire hour I'm thinking you're doing a good job. Just my 2c worth.