8 replies to this topic

[Conny T]

Before our daily cleaning and desinfiction we rinse our equipment and floor with hot water. Since we haven`t got enough hot water "from the tap" we heat approximately 1000 liters cold tapwater - this water are transmitted to a tank in productionarea (seperate piping) and from this tank our lab takes microbiological samples which have been too high according to our legal limits (valid for cold water - 20 cfu/g at 37 oC).
The water is heated to 65-70 oC - temp at use min 50 oC.

For getting the higher level of germs to a lowe level, I am thinking cleaning and desinficting piping and tank, then flushing piping over several times with hot water, final rinse with cold water - and applying a sign to ht tank "always open bottom -tap after rinsing". Then I, hopefully, can be sure that the tank will be emtied every day.

But I believe that our spec for hot water generally will be higher than for cold - and as all equipment is cleaned and desinfected with cold water afterwards, I mean that I can make a spec higher than 20 cfu/g for out hot water.


Please your opinion - and if you know any documantation applicable for my problem please link

[Charles.C]

Dear Conny,

Curious procedure to me but perhaps not to you.
The APC/20cfu @37degC is presumably the EC drinking water limit. Unlikely to change IMO.
The accuracy of measurement may be relevant depending on the actual numbers / yr procedure.
Maybe try the other incubation temperature allowed (22degC) since this increases the limit and may give a more accurate result (if you hv a low-temp incubator).

Some basic data might be helpful -

eg source of water = ?
water before heating has any residual Av. chlorine ?
(if so, would expect APC at 37degC to be approx zero assuming Cl2 residence time sufficient)
APC of water @37degC before heating = ?

APC of water @37degC after heating = ?
water after heating has any residual Av. chlorine ?

APC of water @37degC after exit from piping = ?
water after exit from piping has any residual Av. chlorine ?

An initial zero Av. Cl2 will obviously yield two more zeros.

Two obvious options are (a) initial cold water may be low APC but is still too high after touching the piping.
(b) the heating process and/or piping has simply unacceptably contaminated the water.

Normally even a low residual Cl2 level solves above-type problems. Maybe Denmark does not allow ?.

I daresay you hv thought of (a,b) already.

Rgds / Charles.C

[Conny T]

You`re right - it is a curious procedure and I would like much more like us to have plenty of tap-water (in DK tap-water is withour Cl2, from public watersupply - and all Danish water is drinkingwater quality) and the EC-limit goes for the control with water supplied to us from the public watersupply. Inside the plant the legal demands from the Hygiene-regulation is applied and it states that water for cleaning shall be of drinking water quality - but is rinsing part of cleaning..preparation or cleanup after production ?

I did not know anyone else who had same procedure as us regarding this water for rinsing I turned to the forum - and could not find any doc - except for projects from the Danish Environmental authorities but all about water- treatment- plants - some showing higher levels and some lower levels in hot water.

Never the less I would like to see "how low can we go" on the hot water and will start up with a little project with microbiological tests, cleaning and further tests.

[Charles.C]

Dear Conny,

Indeed Denmark appears to be almost unique in EC regarding anti-Chlorine.(Luxembourg also apparently ). I hope you never experience contaminated water supplies.

Difficult to make much further comment without any numbers.

If yr supply has (37degC) APC = 19cfu/g and output from tank = 100cfu/g, i guess (a,b) both possible defects.

If supply = 1cfu/g and output = 100cfu/g, presumably (b) is the suspect.

Most factories IMEX wash their floor, etc after production. Or perhaps you hv no time after a night shift (which would be unusual also ) ?

Must admit i hv never seen any investigation into the bacteriological area / temperature variables you mention. Confined to D@L presumably.

Rgds / Charles.C

[Conny T]

We do have a full cleaning every day (rinse, wash and desinfect) - my comment was on the matter how to answer to the authorities if they looked upon the matter. I do not think that it is a concerning matter as we always have our wash and desinfection after wards.

And my question only concerned the matter if anyone knew to documentation regarding microbiology in hot water - thankey for your help :-)

[Dr.Des]

It's my understanding that the specification of TVC@37 <20 and TVC@22 <100 only applies to water offered for sale in bottles or containers (Directive 98/83 EC).
Unless that is your product why do you have this spec set for your water? Is there legislation in DKenmark that imposes this spec on waters used for production also, or have you set it yourselves?

Leaving that aside, I would have thought that heating the water to 65-70C would reduce bacterial numbers (provided you hold it at that temperature for a few minutes), so your spec for hot water would than really need to be tighter than that for cold water.

[Charles.C]

Dear Des,

It's my understanding that the specification of TVC@37 <20 and TVC@22 <100 only applies to water offered for sale in bottles or containers (Directive 98/83 EC).

IMEX, the same standard is used by auditors to evaluate plant water supplies if a factory is exporting goods from outside EC to within EC. Within / within the EC, (although I guess you are in an excellent position to know )

Whether Demnark apply some other sanitising treatment to their water in lieu of the forbidden chlorination no idea also. If so, I am surprised that the problem existed for a clean system. Hence the concept of in-plant "sanitisation".

Rgds / Charles.C

[Conny T]

Our Danish Drinking Water Guidance says that water used in foodplants shall meet the requirements ( chemical, microbiological and physical) stated ind the Danish law. You can have a permit to use other water than drinkingwater if you do not have access to sufficient quantities of drinking water or if you for instance have your own well which do not meet the requirements.

And the problem would not excist if time-table was "tighter" (when the water is boiled - as we cannot heat the whole lot at one time - and the tank is not isolated) - and because of not isolated piping. All this means that the temperature is not 65-70 oC when used.

[Charles.C]

Dear Conny DK,

Appreciate yr patience in continuing this somewhat meandering although enjoyable (to me anyway) discussion.

Of course, the exact comments may depend on yr situation, like what you are processing, how, and for whom, eg local use / export.

You are undoubtedly correct that if only local usage is involved, then the local water regulations will also apply. If otherwise, then maybe otherwise (or not).

I presume the alternative water supplies, eg “well”, you mention in previous post hv less detailed (and demanding?) bacteriological requirements. I am rather surprised that variable specifications exist for water to be used for the same application although the general topic of what precise requirements for processing water are strictly necessary has been looked into before from a risk point of view, eg see the attachment below (2008).

 Water quality requirements in the Food Industry (ILSI, 2008).pdf   387.99KB   69 downloads
(Table 8, pg 27 is vaguely interesting)

I agree with Des’s comment that heating the water (already possessing low counts) to temperatures like you initially mention would logically further reduce the vegetative bacterial content. Boiling even more so of course. The existence of significant spore formers might be a bit more problematic depending on the times / temperatures involved but this is an unlikely scenario anyway I guess.

I think yr starting proposal is the best concept to initially check out. (And depending on the actual numbers of course). Should at least give you an idea of the source of the observed effects (assuming yr measurements are accurate enough to reliably detect the differences). Maybe there is something in yr pipe/tank layout which does not like hot water.

Rgds / Charles.C