WEISENBERG EFFECT- PROBLEMS OF STIRRING BIOPOLYMERS IN FERMENTORS

It is the purpose in any engineering design of a fermenter to achieve uniform and homogenous mixing. This objective is to ensire that the content of the fermenter is homogenous and good mass transfers occur between the microorganisms and the surrounding environment.
Frequently though this objective is always kept in mind, the weakest link in the process is the failure to understand the rheological properties of each fermentation broth and the provision of unsuitable stirrers or mixers to achieve this end.
Complications arise due to the fact that most if not all fermentation broth are non newtonian and show very complex properties spatially or even temporally during the fermentation run. Just providing any standard stirrer is not the proper solution to this problem. Each fermentation process have its own unique problems and conditions and almost require its own specific stirrer and mixing regime.
One good example often faced in fermentation industries is the problems of mixing viscous broth. This is often encountered in food fermentation such as yogurt fermentation or fermentation of biopolymers or those involving use of sticky sugar substrates.
In theory we expect any mixing of fermentation broth would result in homogenous conditions, improved mass transfers. In viscous broth we expect the effect of stirring would be to stretch and thin out the broth to improve mass transfers
The problem is during the fermentation mixing or stirring there is the tendency for the broth to creep up the stirrer shaft, instead of being dispersed throughout the fermenter. This effect is called the Weisenberg Effect
The Weisenberg effect refers to a common phenomenon when a spinning rod is placed in a solution containg liquid polymers. This will result in the entanglement of liquid polymers to the spinning rod or shaft leaving the free ends of the polymers in the solution. Tensional forces acting on both ends of the biopolymers will try to reduce the distance between the two ends resulting in the polymers to move along the shaft.
Given time a mass of biopolymers will be cumulated at the end of the spinning shaft of the stirrer.
IMPACT OF WEISSENBERG
1 Extra load at tip of moving shaft will generate extra torque and if the shaft of stirrer is long will throw out the shaft out of its normal oscilation
1 Inefficient mixing as the impellers will be covered by the cumulated biopolymers
3 Entrapment of biomass that will not contribute to fermentation product
4 more downstream problems and loss of time in cleaning the stirrer system

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MAKING YOGURT- PLAYING WITH VISCOSITY

Almost everyone knows how to make yogurt. Yogurt is after all a simple fermentation process using milk as the substrate. The microorganisms involved in the process are . S.Thermophilus, L.Actobacillus Acidophilus and B. Bifidum.
In the process the milk sugar or lactose is converted into lactic acid and other fermentation products such as carbon dioxide, acetic acid, diacetyl and acetaldehyde which contribute to yogurt's characteristic taste and aroma.
It does not take a food scientist to make a simple yogurt. A hobbyist who is willing to ‘experiment’ with ingredients and conditions, and after passing through trial and errors will ultimately be an expert in making his own unique yogurt. p(Though others might not like his product)
However, if you are trully interested in making the perfect or standard yogurt that is marketable you do need to really understand the processes ivolved in making high quality yogurt.
Of course, the preference for a particular type of yogurt depends on the individual. But you need to produce a yogurt product of the highest quality, consistency.
A good yogurt is characterised by its flavour, aroma, appearance and texture. The texture of the yogurt itself is important. Many yogurt are designed to help create or maintain a thick texture.
TEXTURE OF YOGURT
Most people would like to imagine yogurt as viscous but soft enough to flow.The texture of yogurt is measured in terms of its flowability or viscosity.
The manufacture of yogurt itself in reality is complex as the rheology of yogurt fermentation changes with time and stage of process . This would not be a critical issue for home made yogurt involving small volume production
In controlling the viscosity of the yogurt would involve various stages of manipulations such as:
1 The milk used for making yogurt must be standardized and should contain at least 3.3% fat and 12 - 18% Milk Solids
2 Homogenisation should be used to increae the product viscosity
3 Pasteurisation at 98 degrees Centigrade for 3 minutes will help in the coagulation
4 Filtration should be used to removed pockets of whey in the broth
5 Cooling should be carried out in a controlled manner to maintain the integrity of the yogurt viscosity
6 Transfers of yogurt should be carefully carried out by pumping and mixing properly to maintain its viscosity




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MILK FERMENTATION- PASTEURISATION AND STERILISATION

Milk represents one of the most common source of nutrients used widely in all countries and human cultures. There are many kinds of milk available depending on the type of animals used to produce the milk. However, dairy milk or cow milk represents the most popular type of milk used by man.
Milk is so nutritious that not only its ideal for human nutritional requirements but also for the calves for which nature intended it to be in the first place.
It is a sad and tragic fact that lactating cows are the ones used to produce milk which we need in volumous amounts. To do so, these cows are needed to be fertilized, and only after they give birth to calves would milk be produced. Since the cows are meant to be producing milk, I often wonder what happens to the young calves produced once the dairy cows start lactating. Will they be allowed to grow into maturity or will they be slaughtered young ending up as veals?
My apologies for the temporal distraction from the topic…. Just cannot help it!
BACTERIA LOVE MILK TOO!
Milk being nutritious will also proves to be irresistable to the bacteria. Milk is rich with proteins and various vitamins and growth factors is too good a deal to be rejected by the bacteria. Bacteria especially those that are nutritionally fastidious will grow well in milk.
This nutritional attraction for the bacteria will have serious implications for the humans that drink the milk. Not only will the humans have to compete for the milk with the bacteria but the bacteria will result in the spoilage of the milk itself by its biochemical activities. The bacteria itself will be a source of microbial pathogens and diseases.
CONSEQUENCE OF MILK MICROBIAL CONTAMINATION
One of the consequence of microbial contamination and spoilage of milk will be short shelf life of the milk.Attempts were made to solve the above problem not only due to health but economic consequences.
One of the most common ways to reduce microbial contamination of milk is either by killing or removing the microorganisms in the milk.
There are several methods to achieve this but each method will have its own advantages and limitations.
The use of heat or high temperature is commonly used in pasteurisation or sterilisation of milk.
PASTEURISATION
One of the earliest method used in industries to solve the problem is by the process of pasteuerisation. This process is named after the famous microbiologist Louis Pasteur.
In the pasteurisation process the milk is subjected to a high temperature for a period of time which will allow the killing of some of the microbes without really damaging the quality of the milk
In the Pasteurisation process the presence of microbes is reduced…. (REDUCED) and not completely sterilized! The effect of pasteurisation process will be making the milk safer and prolonged the shelf life of the milk. This is of important consequence to the milk industries as more milk can be distributed wider and more profit
It should be noted the concept of pasteurisation is relevant more in the past when refrigeration is not a common household item.
In pasteurisation we see the reduction of the microbes occurred as the consequence of heat being applied. The MAIN OBJECTIVE in pasteurisation is the reduction or destruction of the microbes in the milk.
Pasteurisation is never seen as what EFFECT the process has on the nature and composition of the milk itself and its nutritional value of the natural milk itself
Milk being dominantly protein and amino acids with vitamins and growth factors are affected by heat. Pateurisation will alter the values of the milk itself.
Heating to this temperature, but no higher, does not change the proteins in the milk or the yoghurt so the taste is not really affected.
MILK STERILISATION
The most popular alternative to milk pasteurisation now is using the ultra heat treatment. In UHT the milk is heated to at least 135°C for at least one second. UHT destroys all bacteria in the milk and makes it last much longer than ordinary pasteurised milk. How ever using UHT does cause changes to the taste of the treated milk due to the denaturing of some of the protein components in the milk.





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CHOOSING THE RIGHT STIRRER

One of the most fundamental requirements in any type of fermentor is the provision of a device or mechanism to mix the contents of the fermentor. Good mixing will result in homogenous conditions of the fermentation broth which will help improve good mass transfer leading to an efficient fermentation process.
It is therefore not surprising to see in fermentors the provision of a stirrer or some sort of mixing device to execute this important function. Good mixing is not only restricted in liquid fermentation but also in solid substrate fermentation such as cocoa fermentation and even composting.
Many of us are so ingrained by the ‘brainwashing’ of fermentation literature that a standard fermentor is and always must be accompanied by a standard mixing device such as the motor, shaft and impeller combination. To this influence we are also brainwashed that Rushton turbine is the ‘best’ impeller system. Due to this also we dare not think ‘outside the box’ and are happily satisfied with the standard Rushton turbine despite the fact that the kind of fermentation we are using is not the same as those reported for the standard stirrer. Part of the blame for this ignorance is to be blamed on the users for failing to understand themselves the kind of fermentation they are carrying out, their limitations and failing to appreciate the rheology of their own broth.
The only exceptions to this poor thinking which I observed are those involved in disposable bag reactors and those dealing with the cultivation of plant and mammalian cells. In plant cell cultivation the mixing is brought about by the circulation of the fine air bubbles. In the disposable bag fermentation they use gentle waves which help in the mixing of the fermentation broth.
In the market there are various types of stirrers, shafts and impellers. You must be able to choose the right combination for your purpose.
In this aspects it is important that we need to know :
1 What sort of fermentation are we carrying out?
2 What is the size and geometry of the fermentor
3 The rheology of the fermentation broth
4 The kind of flow we expect for the fermentation
It is only after we have considered the above we custom fit the stirring configurations.
The type of flow generated by the stirrer is important. It is easy to get laminar flow or even non laminar flow for Newtonian rheology. Things do becomes complex if the fermentation broth which we are dealing are of the Non Newtonian type. In certain cases, the types of Non Newtonian transformations become even more complex.

The choice of the proper stirrer will have to be seen from:
1 The shaft component
2 The blades or the impellers
If we are dealing with viscous fermentation broth it is advisable we use shafts with bigger diameter. The length of the shaft too is critical to the efficiency of the shaft
The choice of the type of blades will determine if the flow produced will be radial or axial. Propeller stirrer shaft will produce axial flows. Which will result the flow moving away from the shaft? The inclination or direction in change of rotation will have impact on the direction of the flow
In cases where the blades are arranged on the disc will have flow attributes which will show strong shearing properties. The flow will be radial and directed outwards. Such flow will generate strong axial suction ia top and bottom axis
Impeller stirrer shaft will provide strong radial flows .
There are the so called anchor design stirrers with the shaft fitting in the centre of a “U” shape structure. This effective in generating tangential flows but poor axial forces or movement of the fermentation broth
There are also hybrid stirrers where both type of propeller blades and impeller blades share the same shaft. Usually the propeller blade is located at the top to induce downward flow to the blades with radial flows
It is important therefore in decoding the choice of stirrers the user must understand the rheology and viscosity of their fermentation broth before rushing like a fool to carry out just any fermentation using the ‘standard stirrer’ The best part of these fermentation studies not only they will not be able to determine the optimal fermentation conditions for their fermentation study but they have faith in “ stupid data’ their studies generated.
I just love the way the fools rushed in where angels fear to tread.. Read more!

RELEVANCE OF REYNOLD’S NUMBER IN FERMENTATION TECHNOLOGY

I personally think that there is too much of irrelevant engineering in fermentation technology. The obsession with mathematical equations, models by engineers into fermentation technology just add further to the mysticism of fermentation. It only helps in making the subject of fermentation technology so esoteric and beyond the reach and understanding of most people including the engineers themselves. After all, the abuse of irrelevant engineering and mathematics only serve in trying to make “sense” out of “non sense”. The logic is simple enough. How can you ever claim to control and optimize the fermentation process if you have very little understanding of the variability of the process?
Yes! Such mathematical and engineering studies and experiments will still data or rather “erroneous data” which one can still try to make some sense out of it. The end product will yield wrong and erroneous conclusions. At this point I am not saying that all the engineering or mathematical input are useless or irrelevant.
The trouble is there is a persistent and irritating trend by chemical engineers and biochemical engineers trying to justify their intrusion into the field of fermentation technology and not vice versa! Good examples are the adoption of unit processes in downstream processing. In a feeble bid trying to improve the engineering or mathematical input into fermentation technology they even try to apply Monod’s equation, Lineweaver Burke into the fermentation modeling! How relevant or significant input these contributions are is another question.
We are thankful for the engineers in helping build or design the fermentors we have on the market now. But looking with perspective over time we see there is no real significant development or advancement in the design and structure of fermentors from the days of Fleming industrial production of penicillin. What we are having now are in fact “living fossils” of the old antiquated fermentors. Nothing much has really changed!
Let us look at the application and relevance of Reynold’s Number to fermentation technology.
Historically, the exposition of Reynold’s Number is the keystone to fluid mechanics. It is more and observation on the nature of fluid flow which includes air and liquid such as observed in wind tunnel, aerodynamics and in trying to explain the transformation of simple laminar flow to complex flow turbulence
The application of Reynolds number might be of relevance in aerodynamics of flight where it is necessary to understand the behavior of objects exposed to high speed wind velocity and turbulence. But I cannot really see the relevance of Reynolds Number at the level of fermentor where we are really dealing at low rpm. In fact, laminar flow is not really sought after in fermentor as turbulence is needed to improve the various mass transfer processes during fermentation
To complicate things further the behavior of the fermentation broth is complex in terms of its phases and changes that occur as a function of time. The rheology of the fermentation broth is complex and almost no two fermentation broth are the same. In fact there are so many variables involve which will influence the Reynolds number such as size, geometry, broth type, media composition and even the composition of microorganisms used in the fermentation process
There for do we really need to apply Reynolds Number in the study of fermentation process or is it just a vestigial reminder left by the engineers for us just like the mysterious smile of the sphinx?

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Ave Atque Vale there's a time and place for everything. The place is here. I just need to find the right time.

(THE FOLLOWING ARTICLE WAS TAKEN FROM THE ABOVE BLOG WITHOUT PERMISSION)
Something to ponder....


Sunday, September 5, 2010
I am...
I am a Malaysian.

With that notion firmly entrenched, I bear witness that my country is now 53 years old. It was an age ripened from the valiant efforts of yesteryears’ soldiers who fought for our country’s independence from both internal forces and foreign masters. Though many lost their lives (and are now remembered in memorials such as God’s Little Acre in Batu Gajah or honoured during Warriors Day), the nation was really one in uniting against the perils of communist and rejoicing together when the Union Jack was lowered many years ago. The Malayans simply lived together as religious and racial differences were assimilated to celebrate independence.

Now, Malaysia is an independent nation and unfortunately, the same ‘independence’ has lost its value. While we no longer have to survive communism or colonialism, we are struggling against new evils that were never there. There is a worrying trend of rising racism and religious intolerance between the different races in Malaysia, no doubt fuelled by unscrupulous parties out to serve their own causes. At the same time, we have leaders who preached about ‘Vision 2020’, ‘Malaysia Boleh’, ‘Cemerlang, Gemilang, Terbilang’ and the latest to join the bandwagon is to point one finger upward and utter ‘One Malaysia’.

I am perturbed by how we’re defined by what our leaders label us to be. Far more amusing is that we allow these linguists, the opportunities to ‘reinvent’ Malaysia time and time again when everybody knows the main problem remains unsolved.

Vision 2020 is fast approaching and Malaysia is nowhere near the intended aim of becoming a first world developed nation. Well, if having the KLIA and hosting the Sepang Grand Prix once a year are the cornerstones of a developed nation, then hooray for us. And perhaps Vision 2010 was also dreamt for moments when we burst with pride that our local universities managed to be in the top 200 universities in the world ranking, one that befits our country’s aim of becoming the region’s top education hub. After all, it’s definitely none of our business that neighbouring countries’ universities are mostly ranked in the top 50! Our consolation (and we’re great at finding excuses) could be in the well known story of the hare and tortoise where the tortoise will eventually win. The problem is, we were actually the hare back in those days when our premier university was racing together with NUS, side-by-side.

What the education system in Malaysia today is, at best, one of a handicapped tortoise. We’re handicapped in every sense of the word, from graduates who can’t string a perfect sentence in English to educators who treat teaching with much passion as a toothache. But don’t let that dampen our spirits as we have thousands of graduates jamming the job market! Seriously, Malaysians are really lucky because we must be the only country where students are treated as the shuttlecock in changing the medium of instruction from English to Bahasa at one’s whim and fancy. And because what could be the next smart move to abolish national examinations in place of ‘assessments’, everyone will probably be assessed as smart because now, everybody gets to enter university. If you’re unable to enter one of the many local universities (I think at last count, there was 17), one can always go to the countless private universities mushrooming in every nook and cranny. It’s your choice whether you want to opt for an internationally branded private university or an education institution located on the first floor of a shop lot. If you’re undecided in pursuing which course to take, there is no need to seek out professional advice. Just read the stacks of brochures hurled at our doorsteps promoting quality education for all (but please excuse their glaring grammatical errors and suspicious contact numbers). Finally, Vision 2020 is also envisaged for the nation’s youngsters to grow up as borrowers (and eventual defaulters) as education loans are readily and easily available. It is indeed a bargain to borrow thousands of Ringgit for a degree that could be, in most cases, not even worth the paper they’re printed on.

Further, who could blame us for reveling in Malaysia Boleh when we won a handful of medals back in the 1998’s Commonwealth Games? We were the proud hosts, eager to show that Malaysia is able to stand in the eyes of the world. Okay, so we hosted but what were the costs involved again? I do not believe the accounts have been tabled for the citizens to see just how much the nation has spent for vanity’s sake. And yes, Thomas Cup belonged to us back in 1992. That was the Malaysia Boleh moment that saw every Malaysian kid picking up the racquet and shuttlecock in their bid to be the next Sidek brothers. But it is now 2010 and 5 successive campaigns have passed without the Cup in our possession.
Malaysia Boleh could probably be the explanation why the old Subang International Airport (an important building in our country’s history) was demolished to build, and this was a shocking surprise, another airport! Well, it’s now named as some sort of Sky Park but hey, Malaysia Boleh spend okay. Other governments think thrice and scrimp to get money but let us show you the way. Boleh demolish, boleh build, vice-versa. Either way, money will line certain already well-lined pockets.

Then there’s Cemerlang, Gemilang, Terbilang. Honestly, I do not even know the meaning of those words. Perhaps it is ‘cemerlang’ that it only took our fifth prime minister a few years in office before retiring. One should really consider the previous prime minister’s tenure (and my God, he could almost rival the reign of Soeharto or if he’s a royal, the revered King Bhumibol of Thailand or English Queen Victoria). Well, most of us viewed the fourth prime minister’s reign as a regime anyway. It could also be ‘gemilang’ that government officers were directed to wear ‘batik’ every 1st and 15th of the month. I may not be fashionably inclined but who will actually do serious work when one is dressed up for a reception? I am lost for words in considering ‘terbilang’. I’m taking a shot here but has it got anything to do with the number of shrimps hurled to court for allegations of graft and corruption? Or maybe it refers to the lobsters tiding their sunset years with huge mounts of cash in Swiss banks, happy in the thought that lady justice will not be catching up on them anytime soon.

Finally, the ideals of ‘1 Malaysia’. I would be driving on highways and I’m forced to read huge billboards stating ‘1 Impian, 1 Harapan, 1 Malaysia’. The thing that struck my curiosity is this. Why the need to brand ourselves as 1 Malaysia? My grandparents and parents experienced a life made complete with their friends of different races. Sure, they worshipped different gods but they were united in friendship that transcended the influences of masjid, church or temple. They had no need to use separate tables, hang out in racially defined groups or view each other in a hateful manner. There were no assaults just because the other person belongs to a different race. Most importantly, there was never the despicable need to shout at someone to ‘balik Tongsan, China, India’ or wherever that our ancestors came from. And yet, those are the very things happening now under ‘1 Malaysia’. Isn’t it ironic and downright absurd to claim 1 Malaysia when racial intolerance has permeated into the social fabric of the Malaysian society?

I am deeply disgusted that a school principal uttered derogatory remarks about our friends of the Chinese heritage. I am more appalled that one race is seen to be protected more than the rest when it should be that all must be protected under the flag. I am saddened that May 13 happened (though there exists an irritating doubt that what I learnt from the history books are formulated truths) but enough is enough. It is time that we need to exist as Malaysians without any labels. By strict definition, I consider myself a Malay-Chinese Malaysian (given my mixed heritage) but I will not, at any time support racial extremists who see Malaysia as part of their God-given land. Nor will I condone any calls asking my Chinese and Indian friends to return elsewhere for I would need to go with them as well.

We are all here on borrowed time and the land where ‘tumpahnya darahku’ belongs either to all of us or none at all. Happy 53rd Merdeka and a wish for the upcoming 1st Malaysia Day.
Written by Raja Syarafina RS at 10:47 PM 0 hand prints to be shared
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MY APOLOGIES TO READERS

I am very sorry for not being able to continue writing fermentation technology articles for some period of time as I am currently too busy with some projects
Will continue once the hectic phase is gone. My apologies again
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