Stir plate - throwing bar

I've successfully used a pickle jar on my homebuilt stir plate and that has a slightly concave bottom. I find if my stir bar is being thrown to turn down the speed of the stir plate; how fast you can run it also depends on starter size but YMMV

 

Ones with a dimpled bottom are usually not good to use, Just need a flat surface for the stir bar to rotate. MY homemade stir plate started throwing my stir bar once I bought a 2000 ml flask. Working on building a new one, but I have had good turnout without a stir plate. Hope everything works out man, No experience with marketed stir plates

 

Slow it down.

 

Go on Ebay and get a stir plate from a reputable scientific company. All of the homebrew stir plates are garbage compared to a good commercial one. Have no problem stirring 8 L of broth at work on 20 year old Thermo (IIRC) stir plate.

 

I've used many stir plates on many different containers (in the lab.) You're right - the problem is the shape of the bottom, and the only way to fix it is to increase the # of magnets on your fan or just get a new container.

Or, you can try a real stir plate for $36:

http://www.alkaliscientific.com/en/...stirrer.html?gclid=CIPrzLqI9LMCFad_Qgod7EQAMQ

 

Mine gets thrown every now and then as well. I have to make sure that the stir magnet is first centered (use another magnet to do this) and start at a slow speed. My flask is not completely flat either.

 

Why stir broth?

 

I would think an egg shaped stir bar might work better in the case of a non-flat flask.

 

I use solid bacterial growth medium to make broth, but it requires some stirring before it goes into solution, and further stirring before it clears. If you autoclave some types of bacterial growth media (one type I use; overnight express auto-induction media that has several different carbon sources for expression of genes behind specific genetic elements) without dissolving first, it can scorch and change the chemical composition of the media, screwing up your protein expression work.

 

This is Tom H of www.stir-plate.com. We designed & manufacture the SP-3000 and Black MAXX stir plates as well as the SP-2000 stir plates. While barfdiggs is correct - most good commercial stir plates are great products, the cheap commercial stir plates are junk. The stir plates we manufacture aren't near as good as one of the good commercial stir plates, but you don't pay $300+ for one of our products. Instead, we focus on delivering value for your money.

This post did not start out being a plug for our products but I guess it turned out that way. If you get serious about one of our stir plates and stick with 2 liters I'd suggest the SP-3000 and not the Black MAXX. The Black MAXX is intended for up to 5 gallons and it's over-kill for a 2 liter flask. Black MAXX works great for 5 liters. Either stir plate will work with flat bottom or dome bottom flasks.

 

My stir plate 3000 works perfectly. I've used it for starters ranging from 1.5L to 3L so far and have nothing but positive things to say about it.

 

I think you're better off doing what you're doing (releasing the CO2). Too much CO2 inhibits yeast activity.

 

It's actually $210 bucks, not $36.

 

Yikes, my bad. Time to check eBay and craigslist! Forgot how expensive those little bastards are - around here you can get used lab equipment for pretty cheap (due to all the failed startups).

I have access to stirrers, but I don't use one. I've never had a problem just swirling the flask.

 

I don't doubt that a commercial stir plate would be better (longer lasting, probably), but I have used this one ($45) for a couple of years now, and it rocks for starters up to 2 liters...

http://www.stirstarters.com/

It never throws the bar, but my flasks are flat bottomed. I was kind of surprised to hear that there are erlenmyer flasks that aren't.

 

I use the same unit for smaller starters and love it.