baking bottles

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baking bottles

Postby ilovebeer » Fri Nov 22, 2002 7:10 am

I want to save some time and heat sterilize my bottles in the oven. I have a chart of various temp/time combinations that range from 250F/12hrs to 340F/1hr. What experiences have others had using this technique - what temperature and time combinations have you used, and have you had any problems with bottles breaking? thanks
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Bakin' & other sanitization/sterilization experiments....

Postby Mesa Maltworks » Fri Nov 22, 2002 11:06 am

Just for kicks one time at my lab I evaluated various heat and chemical methods to sterilize or sanitize bottles. I tried the dishwasher method with and without heated drying, oven methods and steam sterilization as well as a host of chemical agents. I assessed the results by swabbing the bottles and plating the samples on wort agar in petri dishes to see if anything would grow. To make sure the results were valid, I repeated each method twice. I also did the same thing with chlorine bleach, chlorine dioxide, peracetic acid and idophor.

Results of the heating techniques:

Baking bottles at 350 deg. F for 2 hours made most of the bottles sterile, but not all of them. I theorized that this was because of uneven heating and convection. I repeated this experiment but added a large shallow pan of hot water on the lowest rack. That change rendered all the bottles sterile. But... every time you do this to bottles they become weaker and are more likely to shatter upon re-use.

Dishwasher methods do not work well at all regardless of techniques. The reason is that the heat duration is not long enough, the water does not come in contact with all of the bottle surfaces and dishwashers have blind spots in them which grow heat resistant bacteria that will infect the bottles. I got bacterial growth on every sample plate I prepared from bottles processed this way.

Steam sterilization (autoclaving) in a pressure cooker for 15 minutes always works perfectly. The disadvantages are that you can't fit many bottles in them and you weaken the bottles.

Bleach works well but take long contact times for maximum effect. The use of bleach can cause off flavors in beer so I avoid it. I was able to grow bacteria from about 7~8 % of the bottles I sampled.

Chlorine dioxide is an excellent sanitizer. The required concentration is very low, it is no rinse, will not cause chloramine related flavors and only takes between 1~2 minutes to be effective. Unlike bleach, chlorine dioxide is stable if stored in a sealed container for about 2 weeks. Therefore it can be used to store equipment and bottles in a sanitized state. Chlorine dioxide will not damage stainless steel unlike bleach. This is my sanitizer of choice. I was unable to get bacterial growth from any of the bottles I sampled.

Peracetic acid works just as well as chlorine dioxide but is much more expensive to use. It also can leave a residual smell like vinegar. In a professional setting, I feel that this is a good choice because it's use can be managed properly but at home I wouldn't recommend it.

Idophor yields very good results quickly, is no rinse and is used at low concentrations. The contact time required is between 5 and 8 minutes. The key to idophor use is to keep the solution temperature at 80 degrees or below. The only disadvantages I can think of are that it can stain equipment and clothes and it has very poor storage stability in solution. I got bacterial growth from about 2% of the bottles I sampled.

In summary, I feel that rinsing bottles immediately after use, covering the neck with foil until the need to use them again coupled with the use of idophor or chlorine dioxide offers the most time efficient, cost effective and reliable method. Heating the bottles and waiting for them to cool will take longer than the above method and will weaken the glass. If the bottles are not absolutely clean you also will end up baking contaminants onto the glass and you may be unable to remove them later. Take the cues from the pros here... almost all of the world's breweries use chemical sanitizers prior to filling them and have very few problems. The only stage heat is used in packaging is to pasturize.
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chlorine dioxide

Postby jayhawk » Fri Nov 22, 2002 2:19 pm

Mesa, what form does chlorine dioxide (ClO2?)come in, powerdered or aqueous? For the storage time you stated, I assume you are referring to aqueous. Also, do you have any experience with potassium metabisulphite (phate)? I can't remember the proper sulphate/ite ending. Apparently this is a sanitizer that is reusable/storable, but is it effective?
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ClO2...

Postby Mesa Maltworks » Sat Nov 23, 2002 10:46 am

Chlorine dioxide is actually a gas... but some chemical companies (Loeffler & Five Star) have managed to stabilize it in water. Five Star sells it under the brand name Starxene, Loeffler sell it simply as chlorine dioxide. You can also generate it yourself. A company called Selective Micro sells a dry form in a pouch with a micro reactor suspension to which water is added. The suggested concentration for sanitization with ClO2 is really low... .5 ~ 1 ppm ! 1 pouch generates 100 litres at .5 ppm or 50 litres at 1 ppm.

In regards to the storage question... yes aqueous. A cool feature of ClO2 is that in a closed environment, the equipment in storage doesn't even have to be in contact with the liquid to be sanitized so it is highly fail safe as long as the equipment was pre-cleaned properly and the concentration is appropriate.

Now... potassium metabisulphite. Effective after extended contact time, but can lead to sulfury off flavors if used as no-rinse. I would avoid it because there are much better alternatives. It's storability is limited to around 3 days once in solution as it will come out of suspension and sink to the bottom of the vessel in a chalky layer. It also is rendered useless as a sanitizer beyond that duration due to oxidation.

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Thanks Mesa

Postby jayhawk » Sun Nov 24, 2002 8:38 pm

Thanks for the reply Mesa. I think I will save for the CLO2 for when I start my micro :) My system right now is working fine. Cheers.
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re: bakin'

Postby ilovebeer » Mon Nov 25, 2002 8:39 am

Thanks for the detailed and informative reply! I picked up some iodophor on the weekend and went with that. I had been using bleach with rinsing for most of my sanitizing, but rinsing bottles was a real pain. The stability problems I hear about iodophor in sol'n - what kind of time frame are we talking here, hours, weeks?

I wonder if there are beer bottles that withstand the heating better than the standard long-neck brown? Or is heat resistant glass like pyrex just too expensive for breweries to use?
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