Helpful Guide to Food Safety and Kitchen Clean-up - guest column

As most readers know, I normally don't post comments that contain links to commercial sites.  I get quite of lot of these, and in most cases, the writers are just trying to get clicks on their own sites.

However, occasionally a message comes along with useful information.   I received an invitation recently to publish a guide to food safety and kitchen clean-up.  This came from Cleaning Building Services New York.

A Guide to Food Safety and Kitchen Clean Up

An essential part of preparing a meal is making sure to use the proper food safety techniques. Without proper safety protocols your food can become contaminated and pass along foodborne illnesses to whomever eats or comes in contact with it. The Centers for Disease Control and Prevention (CDC) states that 48 million Americans become sick from foodborne illnesses each year. Of those 48 million people, 128,000 are so sick that they need to be hospitalized, and 3,000 people even die from the foodborne illness. To prevent foodborne illness from happening to you or your family, it is important to practice food safety protocols while handling, preparing, and storing all of your meals.

Cleaning Up the Kitchen

Keeping your kitchen clean is an important step in food safety. After each meal, it is important to clean and sanitize all surfaces where food was prepared or handled. All surfaces should be washed thoroughly with hot water and soap. For a deeper clean the surfaces can even be washed with a diluted chemical mixture of 1 tablespoon bleach and one gallon of water. All cooking appliances used when preparing the meal should also be washed thoroughly inside and out. An important step that most people tend to forget about is cleaning out your refrigerator. You should be going through your refrigerator once a week to discard any expired items to prevent growing bacteria. Vegetables and Fruits should also be rinsed under water before being consumed to get rid of any pesticide residue. You should always clean your hands thoroughly after touching any raw meats or fish as well, this will help prevent transporting harmful bacteria.

Know Your Temps

Foodborne Illness is caused by harmful bacteria, some of the most common being Escherichia coli, Salmonella, and Staphylococcus. This harmful bacteria can be consumed by eating undercooked foods and can be prevented by making sure all food is being cooked to their accurate internal temperatures. This can be done by using a kitchen thermometer. Checking the internal temperature is especially important when preparing foods like meats, fish, poultry, and eggs. Before preparing a new recipe, be sure to research what temperatures your ingredients should be kept at to avoid them being in a danger zone for the harmful bacteria.

Food Organization

When buying food at the grocery store, look for broken seals and damaged containers before putting them in the cart. Also, be sure to check expiration or sell by dates to only purchase fresh and safe to eat foods. When cashing out in the register line, be sure that your meat or fish is packaged separately to avoid juices spreading onto your other foods. Separation is key when storing your foods away at home as well. You should always store raw meat or seafood below any other foods in your refrigerator and place them in plastic bags to avoid contamination. If possible, use different cutting boards and other cooking utensils for meats or fish and veggies. If not, be sure to clean them thoroughly in between each use. Doing this will lessen the chances of leftover bacteria being transported from your raw meats or fish to your cut veggies and fruits.

Source: Cleaning Building Services

Other material from this source will appear on this blog from time to time.

Declaration:  Safe Food Blog does not endorse Cleaning Building Services, not does it have any pecuniary interest in the company.

I've been served some pretty awfull coffee in my time ...

Many people on Twitter are reporting that a pregnant woman in Alberta ordered a latte at a McDonald's but was served a cup containing cleaning fluid.

According to a report on CBC News, this was caused by the coffee machine still being connected to two cleaning solution supply lines, rather than the milk reservoir.  The cleaning chemical was a mixture of citric acid, phosphoric acid, methyl-trimethyl-3, and 2-butoxyethanol.  There is no doubt that ingestion of this material would be harmful.

It's not clear whether the cup contained hot liquid, though if the machine were set to deliver coffee, but connected to a cleaning chemical supply, it's likely that the cup did feel normal, and since it was a takeaway, it would have been fitted with a lid, so gave no indication that it didn't contain latte.

This potentially very dangerous incident gives a lesson:  if you are a pilot, a car driver, or the operator of a food processing machine, the principles are pretty much the same - the pre-start checks must always be conducted before any start and done properly.

Unwanted passenger on cruise liner

Recently, the cruise liner Voyager of the Seas was struck with what appears to have been a Norovirus outbreak.   'Norovirus' is not a unique organism; there are many different strains, so you can become infected several times during your life.   Norovirus causes diarrhoea and vomiting, which in turn result in contamination of surfaces and generation of aerosols.  If you get virus particles in your mouth, you are highly likely to contract the disease, which appears to have a very high hit rate in exposed people.  (Now do you understand why I never get invitations to be an after-dinner speaker?)

 The virus may be present in the intestines before the onset of symptoms, and may remain in faeces for more than two weeks after recovery.  During all of this time, the virus can be spread. The problem is compounded when a population is effectively captive, such as in hostels or on a cruise liner.  The virus lives for quite a long time on surfaces, so door knobs, bathroom surfaces, lift buttons, soiled bed linen and clothes can be sources of virus particles.  If someone throws up in the dining room, other diners are immediately at risk from the aerosol.  Obviously, if the ill person is working in the kitchens, this is even more serious, as all exposed food and utensils may become contaminated.

The cruise line might be criticised for not promptly informing passengers waiting to board in Sydney about the problem, but the necessary disinfection of a whole ship is a major undertaking, and it appears that the line has made strenuous efforts to protect new passengers from infection.

What can you do to protect yourself?  Rigorous hand washing with soap and hot water (sing Happy Birthday to yourself twice while washing, to ensure that you spend enough time working the soap into hands and under nails) particularly after visiting the toilet or changing baby's nappy and before eating or preparing food.  Do not prepare food for others if you have diarrhoea.  Use of alcohol hand sanitisers may be beneficial, but these are not a substitute for washing.

Wash raw fruits and vegetables before eating them and be sure to cook seafoods thoroughly - Norovirus can survive temperatures of around 60 C.

If you are caring for someone who has symptoms of vomiting and diarrhoea,  handle soiled clothing carefully to avoid generating aerosols; wear rubber or disposable plastic gloves.  Use strong bleach solution to disinfect surfaces in bathrooms etc.  

Odd spot:

In the case of chlorine solutions, more is not necessarily better.  If the solution is made from bleaching powder (sodium or potassium hypochlorite), the more powder we add, the more alkaline the solution becomes.  The active component in a solution of bleach is actually hypochlorous acid.  This acid is unstable and breaks down in alkaline solution.  At pH 10, almost no hypochlorous acid is present in the solution.  Thus, a solution of hypochlorite containing 1000 ppm has a pH of 11.0 - 12.00 and has no active hypochlorous acid, while a solution with only 25 ppm has a pH of 8.0 - 9.0 and so is actually more germicidal than the higher concentration.

Is vinegar just for fish and chips?

My sister in Australia recently sent me a link to the ABC website "Fact Buster".  The page was entitled "Does vinegar really kill household germs?"

See:  http://www.abc.net.au/health/talkinghealth/factbuster/stories/2012/02/02/3407024.htm

The article concluded that vinegar is an inexpensive, non-toxic, biodegradable antimicrobial, but that it is not as good as commercial cleaners.

Vinegar contains about 5% acetic acid.  The article said that this acid kills bacteria and viruses, and suggested that the effect was probably brought about by denaturing the proteins and fats.  If proteins are denatured (their shape and hence functionality changed) the bacteria may no longer be capable of growth.  I'm not sure that the rate of fat trans-esterification would be very high, but it might contribute to damage of the microorganisms.

The action of vinegar on bacteria is quite interesting.  Strong acids completely dissociate into ions.  For example, hydrochloric acid dissociates into hydrogen and chloride ions.  These particles carry a charge and cannot enter the bacterial cell through the cell membrane.
                                         

                            HCl  ⇒  H⁺  +  Cl^-

Weak acids, such as acetic, citric and ascorbic acids, don't fully dissociate; in solution, a significant proportion of the acid remains undissociated and therefore uncharged.  So for acetic acid:

                        CH₃COOH  ⇔  H⁺  + CH₃COO^-

This is where it gets interesting; the weak acid solution outside the cell has a moderately low pH, which keeps a proportion of the weak acid in the undissociated form (the equilibrium is driven to the left).  The uncharged molecule can pass through the cell membrane into the cell.  Here it encounters a higher pH (the interior of the cell is closer to neutral pH) and so the equilibrium is driven to the right and more hydrogen ions are produced.  These ions interfere with the cell proteins and hence cell metabolism, since many cell proteins are actually enzymes.  The cells are either slowed or prevented from growing.  A multipurpose cleaner favoured by my wife claims to "kill 99.9% of germs" ***.  The active ingredient is 3.2% citric acid.

However,  the Fact Buster authors also consulted an infectious diseases specialist, Professor Peter Collignon, at the Australian National University.  He made the point that concentration on disinfection is the wrong emphasis.  Thorough cleaning would practically remove the need for disinfection in many cases - remove the dirt and you remove practically all the bacteria.  Disinfectants may not penetrate a layer of dirt or the slime produced by a bacterial biofilm.  The film may actually neutralise the disinfectant by reacting with it.

The priority should therefore be to remove dirt and bacteria and only then apply a disinfectant if it is required.

***  This claim is ambiguous.  Does it mean that 99.9% of all known germs are killed by the product, or does it kill 99.9% of the organisms on the surface?  These are very different statements.  And never forget: 0.1% of a very large number may still be a large number!

Who ya gonna call - Ghost Busters?

The title is perhaps a bit over the top for a food safety blog, but there is a link!  Last week I spent a lot of time in my car and listened to many old tapes, including the theme song from Ghost Busters.  According to my stats over the past week, a popular search phrase has been "Polysaccharide slime". It seemed propitious to write a short article on bacterial slime.



Bacterial biofilms produce large amounts of polysaccharide.  Polysaccharides are chains of simple sugar molecules.  Some polysaccharides are tough and fibrous but others can be slimy.

Bacteria growing in suspension, the so-called planktonic phase, generally don't produce large amounts of slime.  However, for most bacteria, the normal mode of growth is as a biofilm - an aggregation of cells attached to and growing at a solid-liquid interface.  It has been estimated that when the cells settle on the surface, up to 30% of the genome is switched on or off;  the biofilm mode of growth is very different from the planktonic mode.

Among the changes is the production of large amounts of extracellular polymeric substance (EPS) much of which is polysaccharide.  The EPS glues the cells to the surface and protects them from materials such as detergents, sanitisers and antibiotics.  It also confers some advantages, such as immobilising extracellular enzymes.


In the food industry, we see EPS helping biofilms to remain in processing plant during cleaning, or bacteria spoiling foods such as meats by producing surface slime.  However, not all slime is involved in food spoilage - dextran, produced by Leuconostoc mesenteroides  and Streptococcus mutans and some other bacteria has laboratory and medical applications and may be used in construction of biosensors.

It's the pits - bacterial hideaways

Modern food processing is often carried out in stainless steel equipment - tanks, pipes, valves and conveyors are commonly made of various grades of stainless steel.  We tend to think of "stainless" as not suffering from corrosion.  To a large extent, this is true.  Stainless steel has a natural oxide coating that prevents water molecules from oxidising the iron.

However, stainless steel can still corrode where grain boundaries or embedded contaminants allow water to access the iron.  The contaminants might be grinding swarf from welding or repairs.  Stainless steels may therefore benefit from a process called passivation, in which the surface is cleaned with sodium hydroxide and then treated with nitric acid.  This restores the oxide film.

We use stainless steel in our laboratory experiments and routinely passivate with hot nitric acid.  One of my students used a bottle labelled "Concentrated nitric acid" from the chemistry laboratory to passivate some new samples.  Unfortunately, it appears that the contents were actually Aqua Regia, a mixture of nitric and hydrochloric acids.  (How often have I said that correct labelling is critical in food safety?).  

Chlorine ions are extremely electronegative and react strongly with certain compounds.  They can severely damage stainless steel.

The first photograph shows two coupons treated with the acid mixture.  It is obvious, even to the unaided eye, that the surface is pitted.  Chloride pitting tends to occur at right angles to the surface, so deep pits form rapidly.  Obviously, the use of aqua regia is a very extreme case of chloride attack, but even food materials containing sodium chloride will eventually attack stainless steel.  Even 316 stainless steel, which contains molybdenum that helps to stabilise the passive film, will corrode if exposed to high levels of chloride ion, or if the oxygen level is very low.  This is what may happen under a biofilm, where the bacteria use up the oxygen.  The area then becomes anodic and current flows, resulting in corrosion and the formation of a pit.

I took a couple of coupons to Dr. Jen Wilkinson who runs our Scanning Electron Microscope.  She took the following images, which show clearly the damage to the surface and the deep pits caused by the corrosion.  The second image below shows the interior of the pit.  Bacteria could easily enter the pit and would be very difficult to remove during cleaning.  If the bacteria form a biofilm, they will be protected by the extracellular polymeric substances (EPS) which glue them to the surface and may inactivate disinfectants.  The bacteria will be impossible to remove.

Black Humour

I have been a consultant to the food industry for the last 33 years and in that time, I've seen some things that would be funny if they were not so disturbing.

A few years ago, I was helping a food factory to gain control over the level of contamination in their products.  The company manufactured a very large number of product lines, some of which were essentially assemblies of cooked foods with fresh salad vegetables.  The levels of microbial contamination in finished goods were obviously not under control and sometimes spiked well above the Microbiological Reference Criteria for Foods. 

The company was doing regular wash down of the entire production facility, though their finished goods still showed irregular spikes of contamination.  I began doing regular checks of hygiene in the factory.  I asked them to change the way that the cleaning was conducted, so that there was no food exposed during the cleaning and that the equipment was cleaned top-down.  The product contamination continued.

On several occasions, I pointed out that they were cleaning the food contact surfaces well, but that the fabric of the factory was not being cleaned so well, particularly the floors.  Some of the mutterings went along the lines of "We don't process food on the floor".  Yes, of course, but wet floors allow growth of bacteria in food residues and generation of aerosols, which can settle onto food contact surfaces and in-process food.

The last straw came when I pulled up a floor drain and showed the manager the thick gray biofilm on the fitting.  This can't form overnight or during a shift - it had not been cleaned for at least a week.  The manager responded with "That's not our biofilm".  Being an erudite conversationalist, I said "Huh?".  "No", he replied, "the drains back up and that's how the biofilm gets there, but it's not ours".

Hands up all those who are surprised that this manager successfully managed the company into receivership.  Nobody?  Thought so.

The joy of cleaning (yeah, right)

I was recently interviewed for a forthcoming television programme dealing with mould in the bathroom. I decided to brush up on my knowledge of cleaning chemicals to try to avoid getting caught flat-footed by the interviewer. When you really get into it, the science behind modern cleaning technologies is quite fascinating and more complex than you might expect.

My research team specialises in the study of biofilms. These accumulations of microorganisms and their sticky products on surfaces are extremely hard to clean. Since I have mentioned biofilms in earlier posts, I thought that it might be time to examine them in more detail here.

Pasteur and Koch laid the foundations of modern microbiology by culturing bacteria on solid media in pure culture. This development enabled microbiologists to study individual strains of bacteria without the interference of other types and we have continued to use their techniques. However, it is now generally accepted that bacteria grow preferentially as biofilms – complex communities growing on a surface and surrounded by polysaccharide slime known as glycocalyx. Among other things, this glycocalyx gives the bacteria protection from cleaning agents. Failure to take account of this when formulating cleaners and disinfectants can result in incomplete removal of the film. This is particularly important when the surface is a piece of food processing equipment.

Go and have a look at your beautiful stainless steel kitchen sink or the shower tray. They look perfectly smooth and should be easy to clean. However, when we use a scanning electron microscope to see the surface on the same scale as bacteria, it is clear that the surface is anything but smooth (see first figure). Bacteria can get down into the troughs between the grain boundaries and it’s obvious that getting them out of there is going to be difficult. The difficulty of cleaning is made worse if the bacteria are left to grow long enough to form a proper biofilm. The bacteria produce a sticky mixture of polysaccharides, which glues them to the surface and attracts other bacteria and traps food particles (see image at right).

When we buy a cleaning product from the supermarket, we are buying a carefully formulated mixture of chemicals that has a number of functions: it must bring the chemicals into close contact with the biofilm; proteins, carbohydrates and fats must be solubilised or suspended so that they can be rinsed away; for domestic cleaning it is also desirable that the cleaning product should kill bacteria. (In industrial cleaning, a separate sanitiser is usually applied after cleaning).

To satisfy these requirements, most cleaning products contain a surfactant to break down the surface tension of water (to make it “wetter”) and an alkali to solubilise proteins and fats. Sometimes an acid is used to remove scale deposits. Industrial cleaners for food processing equipment often also contain hypochlorite, which releases hypochlorous acid and ultimately an oxygen radical, both of which are strong oxidising agents that can break down dirt. Because of the potential danger to consumers, domestic cleaning products are usually much less alkaline and generally weaker than industrial cleaners.

I am often asked whether there is an alternative to the “harsh chemicals” used in cleaning products. Well, there are so-called “green cleaners” derived from plant materials, but the principles behind the formulations are the same – combination of surfactant such as an alkyl polyglucoside from palm and coconut, with citric acid and a solvent, D-limonene, from citrus skins. I have heard of white vinegar being used to remove bathroom mould instead of the chlorine-based cleaners. However, even the proponents of such substitutions admit that a lot more effort is required to remove the mould and that it soon comes back. This is partly because vinegar has no surfactant properties.

Successful cleaning requires four things: the right concentration of cleaning product, suitable temperature, mechanical energy (“elbow grease”) and sufficient time for the chemicals to penetrate the dirt and destroy bacteria. The best way to ensure that cleaning is successful is to follow the instructions on the label – the manufacturer has formulated and tested the product to be used in a certain way.


If done correctly, cleaning will remove biofilms from stainless steel. The two images at left show a piece of stainless steel before and after cleaning. The bacteria were stained with a fluorescent dye and observed under UV light in a fluorescence microscope.











However, a successful cleaning operation is only a temporary fix and regular cleaning is essential to prevent biofilms from forming. Like death and taxes, it’s not much fun and there’s really no getting away from having to clean.




Credits for photographs provided by my research group:
First image by Steve Flint and Doug Hopcroft; Second image by Shanthi Parkar and Doug Hopcroft; Third and Fourth images by Shanthi Parkar.

(The description given above is still a simplification of cleaning technology. I have tried to capture just the essentials of the process and the cleaning products).