Subject: Re: RE-freezing spaghetti sauce

From: [email-masked] (J Ralph Blanchfield)
Date: Tue, 19 Mar 1996 19:32:04 GMT

On 18 Mar 96 22:28:29 GMT, [email-masked] (Laurie Kennedy)
wrote:

>
>You will be fairly (but not absolutely) safe.  The problem bacteria fall into 
>two classes, Salmonella and Clostridia.  The former are killed by boiling but 
>the toxin they produce is not inactivated, so once the bacteria have grown the 
>food can't be made fit to eat.  Clostridia spores (their 'hibernating' form) 
>survive boiling but the toxin (VERY dangerous) does not.

Sorry, Laurie, but this paragraph is confused.  Salmonellae do _not_
produce toxin (whether heat resistant or otherwise). They cause food
poisoning by being themselves infective. Moreover, food  contaminated
with salmonellae  _can_  be made fit to eat. For example virtually all
chickens are thus contaminated, and can be made fit to eat by cooking
thoroughly.  Neither clostridium botulinum micro-organisms nor their
exo-toxins are easily destroyed by ordinary boiling. 

One danger is that repeated heating and cooling may well cause
clostridial spores to germinate and the bacteria can start producing
exo-toxin, which may then not be destroyed by mere reheating.
>
>Fortunately both groups of bacteria don't much like acid conditions, so if 
>your sauce had as much tomato as it should (!) the odds are in your favour.  
>If the sauce has been either very hot (60C+), frozen, or thawed but still 
>cold, and never warm for any period of time I'd happily use it again.  Danger 
>signs when reheating the sauce: any odd smell, particularly sweetish-sickly, 
>and any 'fizzing' or gas production.

Some tomatoes are on the borderline of safe pH regarding clostridia,
and instances of clostridial food poisoning have occurred in tomato
products.  Dependent on the other ingredients of the spaghetti sauce,
the pH may be above the safety margin for clostridia and some
salmonellae.
>
>All of that said I'd have to agree with the above quoted comment; balance the 
>potential loss against the very small risk of lots of unhappy people.  Not 
>knowing the food's precise history or your food-handling facilities, care etc, 
>I'd have to say use it yourself, but not for paying customers.  If it's not 
>infected it should keep for many weeks.
>
>Laurie Kennedy

That's a very big "if"

Dump it.

Regards to all

Ralph
******************************************************************
J Ralph Blanchfield
Food Science, Food Technology & Food Law Consultant
Chair, IFST Member Relations & Services Committee
Web Editor, Institute of Food Science & Technology
IFST Web address: http://www.easynet.co.uk/ifst/ 
******************************************************************

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From: [email-masked] (Malcolm Hills)
Date: Thu, 21 Mar 1996 18:55:16 GMT

george erdosh <[email-masked]> wrote:

>As long as the sauce hasn't been standing at room temperature for too 
>long, it should be perfectly safe to refreeze, thaw again, and refreeze 
>even several times. It is the growth of microorganism that is a concern 
>but in a tomato sauce with acid conditions chances are not great that 
>bacteria can survive in any significatn number. Besides, you will be 
>reheating the sauce anyway making it sterile.

I have watched this small thread with interest.

My opinions coincide with those of Mike Leblanc, whom I know is an
Environmental Health Professional, like myself, What I am interested
is however is what is the background of the other posters

ie George, Laurie and KCB

By the why Mike can you repost your home page address, thanks
===========================
Malcolm Hills MCIEH
[email-masked]
===========================

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From: [email-masked] (Laurie Kennedy)
Date: 18 Mar 96 22:28:29 GMT

In article <[email-masked]>, [email-masked] (KCB) wrote:
>[email-masked] (KVacek) wrote:
>
>>What is the reason for the warnings about not re-freezing once-frozen
>>food?
>>Is this a food safety issue, or one of quality? 
>It is a food safety issue. Bacteria grow as the food is kept luke
>warm. These bacteria can come from heat-resiliant spores, or from
>recontamination (the air or general handling or pots that are not
>properly clean) During cooking you may kill most of these bacteria.
>The danger is still present though as some of these bacteria produce
>toxins which are more heat stable than the bacteria and these toxins
>survive the cooking.
>
>>Specifically, I ran a spaghetti dinner for the Lodge on 1/20/96 and had
>>about 6 gallons of sauce left over, which I froze.  Yesterday I thawed it,
>>added a bit of this and that, and served it to about 50 more people. 
>>Afterward, without thinking, I bagged and froze the remaining 1-1/2
>>gallons.
>
>>Now I wonder what to do? 
>I would not use it again catering for such a lorge group of people, as
>if there is a problem, you will have lots of unhappy people. It may be
>safe enough for your own eating, but just cook it up very well first,
>just in case, and use it up ASAP.
>>-Immediately thaw it & give away for use ASAP?
>>-Save it to be used in a week or two?
>>-Dump it?

Laurie Kennedy

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From: [email-masked] (J Ralph Blanchfield)
Date: Fri, 22 Mar 1996 10:36:30 GMT

On Tue, 19 Mar 1996 19:32:04 GMT, [email-masked] (J Ralph

>exo-toxin, which may then not be destroyed by mere reheating.
-- snip --

I am grateful to Laurie Kennedy for his e-mail message in which he has
rightly questioned my statement that the exo-toxins are not easily
destroyed by ordinary boiling.

I should not have used the word "boiling"in relation to the toxins.
Plus inevitably we always have to (over?)simplify in postings.

Botulinum toxins are inactivated by heating at 80 deg C for 10 minutes
[Pierson and Reddy (1988) Food Technology, 42(4), 196-198]. Even
ignoring the protective effect of other components in a real food
system as compared with pure toxins, the "free" toxins would be
inactivated by "boiling" for a few minutes.

However, while most of the toxins are produced by the vegetative
cells, small amounts may be present in the spores, which will have the
same heat resistance as the spores [Fernandez et al (1969), J Gen
Microbiol, 56, 15].

What concerned me was the prospect of repeated heat -- freeze - thaw
-reheat cycles of relatively large volumes of material,  involving
reheating to Laurie's suggested "60C+". Hence my statement that they
would not be destroyed by "mere reheating".

No doubt my concern depended on assuming a combination of "worst
cases". But with Cl. botulinum, one has to base hazard analysis and
action on assuming, and legislating against, the worst case scenario.

Regards

Ralph

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From: [email-masked] (Jan Verhoeven)
Date: Sat, 23 Mar 1996 07:02:47 GMT

>>On 18 Mar 96 22:28:29 GMT, [email-masked] (Laurie Kennedy)
snip

>Botulinum toxins are inactivated by heating at 80 deg C for 10 minutes
snip

snip
--------------------------
Avoid re-contamination (workers-hands) as S. aureus produces
entero-toxin which is heat-stable for a long time at  100 degC.

Regards
Jan Verhoeven