Hi I’m Tristan, this is Magic Maillard Maple,
and today we are thinking about the science behind bacon.
It’s Spring 2021, and with more than 24 million people having had their
first dose of vaccination, the country is slowly moving out of lockdown 3.
Now because the weather is picking up, we fancy taking some more of our long country walks, and
there is nothing I prefer in my packed lunch than the classic bacon lettuce and tomato sandwich.
Now, curing is perhaps one of the oldest food preservation methods known to man, although
strictly speaking, cattle slaughter would have been taking place more towards the end of Autumn
and people would be taking advantage of the cooling weather to help them store the meat
across the long cold winter. But, in the 21st century, meat is 24 hours a day,
7 days a week business, and in the UK about 85,000 tonnes of Pork was produced
just last month. So, if we want to put the B in our BLT, we’d better get started.
With pigs, sheep and cattle, there are a variety of different cuts that we can use,
each with their own tenderness and flavour. Today, we are going to make both streaky bacon,
which comes from pork belly, and back bacon, that is made from pork loin.
To do this, we need to combine our meat with a dry cure mix, comprising salt, sugar and number
one Prague power. This is a good recipe, but for safety reasons, if you are going to make this
yourself be sure to follow the instructions provided by the Prague powder manufacturer.
So how does the curing process increase the shelf life of pork? We have two main preservation
mechanisms – firstly by adding sodium chloride we will decrease the water activity of the meat.
Remember, microorganisms need water to be able to grow – and just by lowering the water
activity below 0.9 we will reduce the activity of several pathogenic bacteria, and below 0.6
we will see little microbial activity at all, although these organisms may still remain viable.
There are two traditional methods of curing meat – the oldest is the dry cure, where the meat is
placed in direct contact with salt mixture, and any resulting liquid is allowed to drain away.
The other is brining, where the meat is immersed is a solution of salt in water.
In both techniques, initially the fresh meat has a lower osmotic potential that the medium
surrounding it, and water and soluble proteins will flow out from the meat.
However, as salt diffuses into the muscle cells, and forms complexes with the remaining proteins,
the osmotic pressure within the meat can rise, and in the case of brining
we eventually see some liquid flowing back into the meat, plumping and tenderising it,
yet remaining unavailable for microbial activity. By swapping some of the salt for sugar,
and making a sweetcure, we can improve the palatability of the final product.
In our recipe we will use hybrid of these techniques.
We start by removing the skin from the pork belly, then we can
dry blend the cure mix. We then rub the mix deep into the surface of the pork……
and transfer the meat and remaining dry mix to a vacuum seal bag.
After vacuum sealing, we transfer to a refrigerator at 5 degrees Celsius for 7
days – turning the pack over every day. After this, we can see that the bacon has formed
its own saturated brine solution – we will wash off the residue then pat the bacon dry.
We also notice that the bacon has turned a deep red colour – this is
because of our second mode of preservation – sodium nitrite.
Saltpetre, known today as potassium nitrate, is an essential component of black powder.
This mixture revolutionised the worlds of warfare, industry and civil engineering,
but saltpetre was used in food preservation long before this most, explosive, application.
Fresh red meat gets it colouration from Oxymyoglobin – the myoglobin protein can store
oxygen as a ligand at its centre, thus providing a reserve of oxygen for the muscle tissue.
Oftentimes, when we see red meat sold in an airtight packet,
it has turned a deep purple colour. Here we have the deoxy form of myoglobin,
and this should turn bright red again on contact with the air. However, as meat ages
we form metmyoglobin, which has an unattractive grey-brown colour we associate with stale meat.
Saltpetre was originally added to meat to keep it a cheerful red colour – microorganisms in the
meat would convert potassium nitrate to potassium nitrite, which is eventually transformed in turn,
to nitric oxide, which combines with the myoglobin to form a deep red pigment
called nitrosomyoglobin. This coloration is very long lasting, and upon cooking
forms the pink pigment Nitrosohemochrome, which is characteristic of cooked ham and
bacon. It was eventually discovered that this preservative also inhibits the growth
of Clostridium botulinum – perhaps the most dangerous of all food pathogens.
Today, we add this material in the active nitrite form, most commonly as sodium nitrite.
We must be very careful in handling this material, and ensure we only add just enough to preserve the
food. According to food additive legislation at the time of recording, dry cured bacon can legally
contain a maximum of just 175 milligrams of sodium or potassium nitrite per kilo of final product.
This value relates to the most recent safety assessment of potassium and sodium nitrites
by the European Food Safety Authority,
which determined an acceptable daily intake of just 0.07 milligrams nitrite ion
per kilogram body weight. Incidents of acute sodium nitrite poisoning are thankfully rare,
and usually occur as a result of unintentional consumption of this material in its pure form.
However, nitrite can contribute to the formation of nitrosamines,
both as meat cooks, and in the gastrointestinal tract. As the consumption of pre-formed
nitrosamines is associated with an elevated risk of colorectal cancers, it is important
to ensure foods are formulated to allow consumers to remain at or below the calculated acceptable
daily intake level. The safety of all food preservatives are regularly re-assessed,
taking into account new data from toxicological and epidemiological studies. Importantly, ADI
applies to the chemical in question from all food and drink sources – and when usage limits are set,
the typical consumption level of different food categories are taken into account.
Now, practically speaking - weighing less than a gram of anything is difficult to
perform accurately and repeatably without a set of professionally calibrated laboratory grade scales.
As such, butchers and home curing enthusiasts can turn to Prague powder. This is a blend of salt
and a small amount of sodium nitrite – in our case 6.25% by weight.
By diluting this potent preservative with salt,
and dying the mixture bright pink to prevent misidentification,
we make this material much safer to handle during day-to-day food preparation.
So back to our bacon. After removing the salt, we need to place bacon back in the
fridge overnight to dry off. During this time, we will form a protein rich outer skin
called a pellicle – which is especially important if we wish to smoke the bacon later.
After this, I just need to slice it up,
pop it into a vacuum pouch, seal and store. As I plan to use this bacon later,
it should be fine to store in the freezer. However, what if I prefer smoked bacon?
At the end of this process, we can take the cured meat, and then ‘cold smoke’ it. Here
we can see a diagram of a smokehouse, where smoke from a wood fire is diverted into an
area containing the meat. The idea is not to cook the bacon, but to dry it out further,
add a smokey flavour, and most importantly add a protective antimicrobial coat. This process
further enhances the keeping qualities of the bacon, and is another example of ancient hurdle
technology - where several preservative concepts come together. Let’s see this in practice.
We start with a wood fire. Different woods imbue different flavours - apple, oak,
and beech are particular favorites. However, resinous woods such as pine should be avoided
as these make a bitter smoke. Wood is largely comprised of cellulose, hemicellulose and lignan.
Burning these will release a variety of caramelization and pyrolysis
products that are antimicrobial, as well as volatile phenolics that have
antioxidant properties – both aiding the long-term preservation of the meat.
As the fire burns hotter, we will also release polycyclic aromatic hydrocarbons – these are
carcinogenic compounds commonly released during the burning of organic matter. Again, there are
legal limits for the levels of PAHs in foods, and the production of these compounds can also be
decreased by good practice, such as restricting air to the fire to keep the temperature down.
So having seen the whole process, I’m sure some of you are inspired to make your very own tasty
bacon, however others might be less keen. How can we balance the idea that processed meat
isn’t always be the healthiest choice, versus the fact that we’ve been consuming foods like this
since at least the middle ages? In my opinion, part of the answer comes down to availability.
Up until quite recently in human history, plants played a much larger role in our daily diet,
and certainly there is plenty of evidence to suggest that reducing consumption of red meat
and processed meat can have benefits for human health, as well as the wider environment.
Nevertheless, ‘everything in moderation’ as they say – so we are going to take our packed lunch,
some healthy dog treats, and get out and go into the fresh air.
Happy spring everyone and see you next time!