Bacteria in curing

[Vernon Smith]

Come on all you microbiologists and answer some simple questions for the benefit of a mere mortal. I acknowledge that undesirable bacteria must be inhibited and desirable bacteria must be encouraged during the curing process of bacon, ham, etc especially when KNO3 or NaNO3 is present. Some of the desirable varieties will convert NitrATE into NitrITE and then to NO'X' that preserves the meat. Many years ago as an undergraduate I learned in organic chemistry that a 10 deg C rise in temperature doubles the rate of an organic reaction, including metabolism. The type of bacteria under discussion here all metabolise at about the same rate at a given temperature. Why then do all the curing instructions stipulate that curing should take place under refrigeration at 4 deg C? At this low temperature 99% of bacterial metabolism ceases so not only will the undesirables be inhibited but the desirables working on the KNO3 will too. My grandfather kept a brine tub in his butchers shop and I don't recall it being refrigerated. I dry cure bacon with 3% KNO3 in the cure at 8 deg C and it works well because the bacteria are all working albeit at a low level. I therefore assume the desirables are doing their job on the KNO3 and preserving the meat before the undesirables get a chance to get in on the act. Any feedback, theoretical or practical, will be gratefully received.
Regards,
Vernon Smith

[saucisson]

The type of bacteria under discussion here all metabolise at about the same rate at a given temperature. Regards,
Vernon Smith

Not necessarily Vernon.

Bacteria grow in many environments from arctic oceans to hot springs, so the optimum growth temperatures do in fact vary considerably. To refresh your memory, without intending any offence

There are three main classes:

Psychrophilic = Cold loving; optimum growth at 0 - 20C
Mesophilic = middle living; optimum growth at 30 - 37 C
Thermophilic = heat loving; optimum growth at 50 - 60 C

Clostridium is a mesophile and its optimum temperature for the variety(s) found in meat is 35-40 degrees C.

The nitrate converting ones are most likely originally soil based and probaly have a much lower optimum temperature, and can still operate in a fridge. (This last bit is speculation!)

Edit:
lactic acid bacteria, which included types often used as starter cultures for meat fermentation, were effective at inhibiting Listeria monocytogenes. Growing even at temperatures as low as 39 degrees F (3.8 degrees C), which is the optimal temperature for refrigerated foods.


Hope this makes sense!

Dave

[Oddley]

Right let's see if I can get my thoughts in order here.

The high concentrations of salt in a brine eg: somewhere over 10% will inhibit most bacteria including botulism (Read on the FDA site) there are a few that are salt resistant. Most bacteria are not anaerobic so need oxygen to survive. So with these two levels of safety a little higher temp won't do any harm IMHO I'm talking about a few degrees here as bacteria can live with very little oxygen so a little bubble near the surface of the meat would be enough, Too high a temp and the bacteria propagate at an enormous rate.

The main culprit for the conversion of nitrate seems to be micrococcaceae. Whose optimal temp seems to be between 25-30 oC. but will I believe grow down to 10 oC.

The low temp is another safety level and the more safety levels the better as far as I'm concerned.

So at the end of the day the choice is your's

EDIT: BTW I have some ham in a saltpetre brine cure atm at about 4 oC (Nearly run out of cure #1). If it fails I'll know if the temp is too low.

[Lee]

The "nasty" bacteria will tend to grow much faster than "nice" bacteria at higher temperatures, so would rapidly overwhelm any of the "nice" bacteria if meat was left at elevated temperatures.
Clostridium botulinum (which is a soil bacteria incidently) will only cause problem in anearobic environments, which is why it's a safety problem in canned goods, as well as our beloved cured meats, and why the nitrates/nitrites are in there to stop the buggers sporulating and doing us damage.
I think....

[Lee]

The "nasty" bacteria will tend to grow much faster than "nice" bacteria at higher temperatures, so would rapidly overwhelm any of the "nice" bacteria if meat was left at elevated temperatures.
Clostridium botulinum (which is a soil bacteria incidently) will only cause problem in anearobic environments, which is why it's a safety problem in canned goods, as well as our beloved cured meats, and why the nitrates/nitrites are in there to stop the buggers sporulating and doing us damage.
I think....

[Vernon Smith]

We seem to have at least three microbiologists in the camp. Gotcha! You are all doing nicely and no offence Saucisson, we're all playing for the same team:wink:. I've only written two PhD theses and there seems another in the offing here . But no, I'll leave it to you Dave it seems more up your street than mine. Thanks for your input, yours too Oddley and Lee.

As I see it, NO3 converters tent to be psychrophyllic and clostridium is an anaerobic mesophite so curing at 8 deg C should not cause problems and I have had none. No botulism poisoning from my bacon or sausages yet!!! I note that salami are incubated at around 30 deg to kick start the lactobacilli before the drying stage that takes place at around 8 deg. My good ol' 8 deg therefore seems to be the panacea for small goods and bacon curing.

Oddley says that 10% brine solution inhibits most bacteria but I am confused by this definition. I use Paul Kribs recipe that uses 1 kg salt and 1 kg brown sugar in 6 ltrs of water (16.66% salt). I add 3% KNO3. Is this what you mean or do you mean 10% salt must be taken up by the ham? My 6.5 kg ham that I put into cure today would therefore have to absorb 650g salt to be safe. Remember I intend cold smoking at 25-30 deg when curing is finished. Sorry if I am being dim!
If your'e feeling brave Oddley why not raise your current ham curing temperature to 8 deg? Dave says NO3 converters are psychrophyllic and clostridium is a mesophyte. The temperature gap is large so you should be safe enough.

By the way, I think the definition "anaerobic" also needs clarification. Lee correctly points out that clostridium botulinum is anaerobic. Cold water in fact contains more dissolved oxygen than the atmosphere (fish breathe too) but most is expelled by boiling. It therefore seems to me that boiling the brine and expelling the oxygen is counterproductive because it creates near anaerobic conditions that clostridium needs.
What pearls can you offer now, my gurus?
Best regards,
Vernon

[saucisson]

Hi all,
The more input we have the better! I'm certainly no expert though my backgound is biochemical/medical science.

Dave says NO3 converters are psychrophyllic and clostridium is a mesophyte. The temperature gap is large so you should be safe enough.

I speculated that this is the case, and am still searching for any proof. It may turn out they are mesophytes too.

In the mean time here are a few pearls I have dug up:

1)Salmonellae do not grow at temperatures below 5.2 �C (41 �F), though hopefully this is of more concern to chicken curers.

2)Staphylococcus aureus has been shown to grow at temperatures as low as 7 �C (45 �F), but the lower limit for enterotoxin production has been shown to be 10 �C (50 �F)

3)There are very few true psychrophilic organisms of consequence to foods. Psychrotrophs such as L. monocytogenes and C. botulinum type E are capable of growing at low temperatures (minimum of - 0.4 �C [31 �F] and 3.3 �C [38 �F], respectively, to 5 �C [41 �F]), but have a higher growth optimum range (37 �C [99 �F] and 30 �C [86 �F], respectively) than true psychrophiles.


So it doesn't matter what their optimum growth temperature is, what concerns us curers is their minimum growth temp. C. botulinum types A and B, the ones found in meat, we now know are mesophytes and grow best at 35-40 degrees, however they do not grow below 10-12 degrees C, so we are safe there.

I'll continue to dig, unless anyone begs me to stop

Dave

[Wohoki]

I'd beg you to keep going. Good work Dave.

I might end up poisoning myself, but it won't be through ignorance

[Oddley]

Vernon Smith, What I meant by 10% was >10% of the brine weight. It is actually good practice to have around 15% salt of the brine.

If I could raise the temp a bit I would, atm moment it's a choice of 4 oC or 20 oC.

I didn't know Paul Kribs had posted a brine recipe, I'd love to have a look at it can anybody point me towards it. I thought he used ready made mixes. Well good for him. I like to see new brine recipes.

[Oddley]

Vernon I'm now confused.

I use Paul Kribs recipe that uses 1 kg salt and 1 kg brown sugar in 6 ltrs of water (16.66% salt). I add 3% KNO3.

I have analysed the recipe you gave and the results are:

1 kg salt (12.1249 %)
1 kg brown sugar (12.1249 %)
6 ltrs of water (72.7493 %)
247.5 gm KNO3 (3.0009 %) (Ingoing 3001 mg/kg)

Total Brine Weight 8247.5 gm

As you can see you said the brine contained 16.66% I have worked it out too 12.1249 %. You say you have added 3% KNO3 (Potassium Nitrate). I have calculated it as 3001 mg/kg.

This is far too much, when the usual amount for a non air dried meat is 500 mg/kg. This is bordering on dangerous.

[Lee]

Can I throw pH into the mix as well!
At a low pH (~4.0), Cl. Botulinum won't grow, which is why commercial food and be pasturised when it's acidic, but needs to be sterilized when it's higher than pH 4.5 (one reason why shop bought tomato sauces tend to taste better than creamy ones, they havn't been nuked in a retort).
It's not actually the Cl Botulinum growing that causes the problem, it's the spores germinating (which need anaerobic conditions, by which I mean a complete absence of oxygen, not just a lower amount than usual, as with your boiled water example).
Hope somebody finds that interesting, I'm a microbiologist you see, so I have no real friends and never get invited to parties

[saucisson]

Hi Lee,

If you're a microbiologist I hope you can check what I'm writing is correct. It's vitally important we don't draw any wrong conclusions here.

Oddley correctly narrowed our nitrate convertor down to micrococcus. The one we want is micrococcus aurantiacus. Now as far as I can work out these are mesophiles and grow best at warm temperatures. The fact that recommended curing temperatures are generally quoted as from 2-5 degrees C suggests that they are also what are known as psychrotrophic, that is they don't prefer cold temperatures but can tolerate them. I think a critical question here is are they actually growing at these low temperatures or just surviving and doing the nitrate conversion we want that helps wipes out any Clostridium. Micrococcus are often mentioned in terms of food spoilage so it's entirely possible that if they grow too much they will spoil the meat all by themselves.

Anyone have a copy of Allen A Kraft's book 'Psychrotrophic Bacteria in Foods' lurking amongst their cookbooks? Lee?

My tentative conclusion is that in an ideal world you cure at under 5 degrees C but that so long as you stay under 10 degrees C the major nasties are too cold. The only caveat is that Enterotoxigenic Escherichia coli can grow down to 7 degrees C.

Dave

[Oddley]

Lee I'm very interested. While I have you cornered at this party I would like to ask you a question. But first I got this from a Swiss commercial Website. The page is sadly down now.

Saltpetre (as sodium or potassium nitrate) or nitrite curing salt (i.e. a homogeneous mixture of table salt and a maximum of 0.6% sodium or potassium nitrite) are used as curing substances. These are broken down in several steps to nitrogen oxide , which is bound to the muscle pigment myoglobi n (either to reduced myoglobin or to metmyoglobin). Legally prescribed limits for the nitrate or nitrite content refer mainly to the residual content in the product (cf. Additives Ordinance, Annex 7, point D.8.2).

Compared with nitrite, the addition of nitrate should result in a somewhat darker meat colour, a more intense flavour and more uniform colour throughout larger pieces of meat.

Nitrate is primarily used for curing longer-aged raw sausages and raw cured products. It is converted to nitrite by bac terial nitrate reduction (originating from micrococcaceae) with fairly high pH-values and then transformed through acid-dependent processes to nitrogen oxide and nitrate. Bacterial conversion itself is a tricky phase during curing and if excessive amounts are added or production conditions are less than optimal, this can lead to greatly increased nitrate levels in the end product due to insufficient development of the bacteria which create nitrate reduction. Care should also be taken that the first phase of the curing of longer-aged raw sausages and raw cured products is to a very high standard especially due to the high water activity values (a w ) and pH-values in the raw materials. Conversely, n itrate has the effect of delaying the bacterial reduction to nitrite when the correct environmental conditions are maintained so that higher nitrite concentrations in all phases of production can be prevented. This may be important mainly in connection with the recently noted prooxidative effect of the nitrite in that this seems to allow fat oxidation to speed up.

http://www.alp.admin.ch/

As you can see the bacteria they think is responsible for converting Nitrate to Nitrite is micrococcaceae.

My question is "if we have anaerobic conditions plus 15% of brine salt how can micrococcaceae survive long enough to convert Nitrate to Nitrite."

I've been thinking about this for quite a while.

[Lee]

Hmm, I would think that at low temperatures (fridge) the micrococci your talking about would be surviving, but not actively metabolising (which is what you want). However there are going to be bacteria (possibly including these micrococci) that are metabolising to a greater or lesser extent (or meat would never go off in the fridge), and it could be these others that are respeonsible for the conversion. I don't think the nitrogen cycle relies soley on micrococci???
I guess that slow steady metabolism is what you want in a curing process
So chilling the meat works. In non fridge dry curing (salami), the brakes are put on by the lowering water activity (I'm hypothesising now) to the same effect

[Oddley]

But are these bacteria salt tolerant to 15%. It just don't make sense. Sorry to keep on at you Lee but you shouldn't have admitted being a microbiologist...