Double-boiling an erlenmeyer flask's contents

With the recent thread(s) about people cracking their erlenmeyers on non-gas cooktops, I set-out to figure out what it would take the get to contents of an erlenmeyer flask to 212F.

In this little experiment, I already had 1 quart of wort made from a previous starter that failed to start. I decided bring this 1 quart to 212F to kills any yeast (or others...), and I figured (not sure if it's true) that dead + popped yeast cells would provide food for the new yeast.

I know that my tap water boils at 212F like most everyone (except for elevation, I know), and I also know that heat transfer between two very close temperatures is quite difficult. I decided to improve my chances by using plain old salt, which I gathered would increase the boiling temperature of water by a few degrees.

So I loaded up my flask with the 1qt of wort, I loaded a large sauce pan with some water, about 2-3 quarts (until the water level was about 1" above the flask's contents), and added about 1/2 cup of salt.

As an FYI, the foil remained on top of the flask at all times, except when taking a temperature measurement pre/during the boil, and remained on at ALL times post-boil.

I brought this to a boil, and the first thing I noticed was that the flask was dancing around from the steam being generated by the boil. I did some quick thinking and I grabbed two knives from the drawer, plunked them in the pan, and balanced the flask on top of them. It seemed to help a good bit.



I measured the boiling temperature of the water, and it was right around 216F (with the 1/2 cup of salt).

I also measured the temperature of the liquid inside the flask, and it was climbing gradually, eventually reaching about 200F where things were plateau'ing. I decided it needed more heat.

I added some additional salt, about 1/4 cup more, and this brought the boiling point of the water to about 218-220F. I continued this semi-vigorous boil of the water, eventually reaching a dead-on 212F in the flask, but it never reached a boil. This in itself wasn't a problem for me, as the wort had already been boiled and the hot break had been removed.

I held the temperature at 212F for 5 minutes, at which time I turned off the heat, and started cooling things. I filled my kitchen sink with about 2" of cold tap water, and put the sauce pan in the sink. This was an initial cooling down, and prevented any burns to the sink itself. (always a good idea to prevent scorching of sink or counter tops!).

After a couple minutes, I started a moderate trickle of water into the sauce pan, effectively reducing the temperature of the water in the pan gradually, to prevent thermal shock to the flask. I stirred the flask occasionally to do heat transfer.



I got to the point where the bottom was moderately warm (I'd say 90-100F) and the neck was hotter (about 140F may be?), so I carefully trickled tap water onto the neck to reduce that temperature too.

I did a final fill of the pan with tap water, added two large handfuls of ice, stirred that around, and let the flask cool down to where I knew I'd be OK to add yeast. I'm estimating that the contents were at about 75F. I let it sit on the counter for may be 10 minutes, to make sure that the inside temperature was even throughout the flask.

I added my stir bar which had been sitting in sanitizing solution, along with the tongs that were to be used to drop it in the flask.

The boiling salt water made a bit of a mess on the glass cooktop, but I was able to clean it easily once it had cooled down.



Overall

The heating time of the contents was about 25 minutes. Yeah, it's slow. The problem due to the small temperature difference between the boiling salt water, and the target temperature of 212F. That did not surprise me at all actually, it's very similar to a wort chiller when the 2 temperatures are close to each other.

The cooling time was about 15 minutes, not too bad really.

Bottom line

It's viable. It's not great, it's slow, but it works.

I actually considered using vegetable oil as the medium. It has a much higher boiling point, and would greatly improve the heat transfer. However, I got concerned that if I got the contents to a boil, and that there was a boil-over, that the liquid falling into hot oil could make for a dangerous mess, and even possibly flammable if the oil escaped the pan and fell on the cooktop.

If anyone has ideas about another *cheap* medium to replace the water, I'd be all ears.

M_C

Interesting experiment.

Being the rebel outlaw that I am I currently boil in a flask directly on the glass surface of our electric stove (which is very similar to the stove you have pictured here) and I haven't had any issues so far with the flask breaking. Though it does make me nervous when I do this so I always watch it very closely while it's boiling. I also have the temperature set to medium so it's just hot enough to maintain a slow, steady boil instead of cranking the heat to high.

I've considered boiling outdoors on a small gas burner intended for camping but I haven't tried this yet.

Seven said:

Interesting experiment.

Being the rebel outlaw that I am I currently boil in a flask directly on the glass surface of our electric stove (which is very similar to the stove you have pictured here) and I haven't had any issues so far with the flask breaking. Though it does make me nervous when I do this so I always watch it very closely while it's boiling. I also have the temperature set to medium so it's just hot enough to maintain a slow, steady boil instead of cranking the heat to high.

I've considered boiling outdoors on a small gas burner intended for camping but I haven't tried this yet.

Click to expand...

FYI, I use a cheap $9 hot plate with a DIY trivet to boil my starters in a 2 liter flask. I have found a setting that will reliably bring the starter to a gentle boil without boiling over. Hooked up to a timer, it's a set and forget method. I first dissolve the DME in hot water using a saucepan and transfer it to the flask. It's autopilot from that point on. Most of the time I just let it cool naturally. When in a hurry, I use a water batch, but that's a rarity these days.

Catt22 said:

FYI, I use a cheap $9 hot plate with a DIY trivet to boil my starters in a 2 liter flask. I have found a setting that will reliably bring the starter to a gentle boil without boiling over. Hooked up to a timer, it's a set and forget method. I first dissolve the DME in hot water using a saucepan and transfer it to the flask. It's autopilot from that point on. Most of the time I just let it cool naturally. When in a hurry, I use a water batch, but that's a rarity these days.

Click to expand...

Care to share your trivet design?

M_C

I used to use my microwave when I still boiled in the flask, I'd get I to boiling then set it 30% power to keep a slow simmer going

I have a glass cooktop and looking at it when the power is on I see that the element is a bit below the glass. I decided that the heat would be fairly even as opposed to sitting directly on a coil element. I turn on the heat to medium for a few minutes to let the flas warm up a little. When cooling it I put a pan in the sink with hot tap water then start adding cold water. I really have no fear that I am going to "shock" my flask..

I also use a drop of Fermcap-s and have no problems with boil over.

Misplaced_Canuck said:

Care to share your trivet design?

M_C

Click to expand...

The trivet is simply a grate that I salvaged from an old gas stove. I just place it over the electric coils to prevent direct contact with the electric coils. You can make a simple trivet from a wire coathanger or other heavy steel wire. A star shape is easy to make and works well. It need not be anything fancy, although I would like to make a wire one in the shape of "Hello Kitty" maybe!

Shockerengr said:

I used to use my microwave when I still boiled in the flask, I'd get I to boiling then set it 30% power to keep a slow simmer going

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I'm not sure that my microwave is tall enough to fit a 2L erlen... I'll have to look.

M_C

Misplaced_Canuck said:

I'm not sure that my microwave is tall enough to fit a 2L erlen... I'll have to look.

M_C

Click to expand...

It don't fit. DOH!

M_C