Accurate readings

So I've bottled 4 batches of homebrew so far and one thing I am noticing is a banana/cidery flavor that is present in all of them. The diagnosis is, according to my searches at least, most likely high fermentation temperatures.

I try to keep my ambient temp on the low end of the yeast's temp range but I have also been reading that the process of fermentation can cause rises in the beer's internal temperature. That leads me to question how accurate the readings I am getting from my fermometer are, which I am thinking is not very since 3 of the crystals are colored at any given time.

So my questions are: do you think this is the cause of my off-flavors? And if so, is there a better way to monitor my beer's temperature vs. the room temperature so I can better control my fermentation?

I've found the stick on thermometers to be pretty accurate. Usually the middle reading or the green number is what is closest to your internal temperature. Usually the banana/cider is a flavor created in fermentation. It's not always high temperatures, it can also be large temp fluctuations or stressed yeast (unhealthy, underpitched etc.) Swamp coolers are an easy and cheap way to keep the temps down and the added thermal mass helps protect against large and fast temp swings. Just put your fermentor in a tub of water and use frozen water bottles to keep the water nice and cool. Change them out periodically to keep the temp steady.

Are you using dry or liquid yeast? Creating a starter if liquid yeast? Re-hydrating if dry yeast?

Well like I mentioned I try to keep the ambient temp constant although I'm sure it fluctuates a couple degrees between night and day temps..I don't have a means of controlling it other than using the house thermostat. I think I might skip the swamp cooler altogether an invest in an external controller and mini fridge since I tend to be a set it and forget it kind of guy

As for the yeast, my first two batches were made with rehydrated dry yeast, and the last two with liquid yeast, one with a starter and my most recent one I just pitched straight from the activator pack. I know that is usually frowned upon, but it was pretty low grav (.041) so I figured it was okay. It'll be a few weeks before that is old enough to judge though.

Sounds like your on the right track.

1. what style of yeast are you using? if you use german or belgian yeast, it will taste like that regardless of temperature.

2. one option: try to look at the weather forecast and only brew on the day before there is a couple of days with a high temp of 65. then it will be easy to keep your house at 67 degrees.

3. if you drink the beer before it is fully carbonated, the priming sugar will cause that taste.

4. how long does your fermentation take before it stops bubbling, and how thick is your yeast cake? if you don't aerate adequately, your yeast will not multiply. therefore your fermentation will take a long time, you yeast cake will be very thin, and it will get stressed/overworked. therefore it will cause that taste.