- For almost a century, it was accepted that
the holes in Swiss cheese came from carbon dioxide,
produced by the fermentation bacteria
that convert milk to cheese,
and that just sort of... happened automatically.
That's written in countless articles.
It's what's all over the internet, and it's almost true.
About 30 years ago, Swiss cheese makers started to notice that
the holes, the technical term is eyes,
were getting smaller and less frequent,
and scientists wanted to work out why.
Specifically, the scientists here at Agroscope,
a Swiss government-backed agricultural research facility,
where, for science, they have a lot of samples of cheese,
and, more importantly, samples of the bacteria that make it.
- It's skim milk, and about one to five billion cells of
lactic acid bacteria per milliliter.
They have a shelf life of about 10 to 14 days,
so all year round, every week,
the cultures are freshly made and sent to our customers.
We are a research station.
We have our collection of strains,
but we are also a producer for these cultures.
We have the genomes of almost all the bacteria
that we have in the collection here,
and we know what parts of the genome
are responsible for some effects on the cheese.
- From the beginning of the 20th century,
microbiologists went to the different dairies
all over Switzerland
and took the cheese and different products,
like whey or the natural whey cultures,
and isolated bacteria from there.
At that time, each cheese dairy
had its own culture to produce its own cheese,
and each one of these cultures was the result of
decades or centuries of evolution, of selection.
Many of these dairies had to close down
or they switched to the commercial starter cultures,
and these bacteria that made up the cultures
would have disappeared if they hadn't been collected.
So, the collection still expands.
We have around 15,000 isolates.
All of the strains of our collection
are frozen at -80°, and for the most important ones,
we also freeze-dry them.
Each strain that we store here has a backup on another site.
- So, each cheese has its own unique bacterial culture
stored in the archive back there
and regularly produced in these bioreactors.
The difference between Emmental and Gruyère
is partly to do with technique,
but it's also the bacteria that make it,
and those bacteria are valuable.
- All the bacteria that we have here in the collection
are owned by the Swiss dairy industry
to have a competitive advantage.
Our bacteria are not better than other bacteria,
but they're very regional, very special.
- Some of the cheese types are legally protected,
and to do that, they have to use some special bacteria.
We call them marker bacteria,
because they bear a very specific sequence of DNA
that we are able to detect
in the cheese during the production,
but also at the end of the ripening,
and by detecting this small piece of DNA,
we are able to say, "Okay, this is the right cheese."
- It turns out that cheese fraud is a thing.
There's a market for fake, cheap Swiss cheese,
and in everyday English, particularly in North America,
there's also no distinction between Swiss-type cheese
and the specific Swiss cheeses
that are made here near the Alps, the ones that have
legal protected status marked on the packaging.
So, Swiss dairies can work with the researchers here,
they can order the bacterial cultures, or just get advice,
but it is strictly just for the industry in Switzerland.
There are trade secrets here that are guarded carefully,
and which I was not allowed to even see, let alone film.
- We regularly develop new cultures
together with the cheese industry,
but because you have always to wait
the ripening time for the cheeses,
it takes always several years to develop a new culture.
- So, a few years ago,
the team here had to answer the question,
why aren't there holes in the cheese anymore?
- We produce here the cheese,
but then they go down to the cellar.
Most of the cheeses have to age
between 3 months and 12 months.
At several time points, we take samples
to analyze them in the laboratory.
For the analysis of the holes,
we use X-ray and we use also computer tomography,
so then we really can count the holes,
but we also see the distribution in the cheese.
- The bacteria that are responsible for making these holes
produce propionate, acetate, and carbon dioxide,
and this carbon dioxide is produced in the cheese
and aggregates all around impurities.
The more the bacterium produces this carbon dioxide,
it accumulates and builds these holes.
These impurities capture the carbon dioxide
and then a bubble forms and grows.
- They found that the milk was too clean,
so we didn't have any dust in it,
and this was because we had closed milking systems
so the dust could not get into the milk.
- Everything improved the last decade.
So, the milking process is hermetically closed now,
and in former times, in the barn,
you had always this hay dust everywhere,
and it came also into the milk.
- We tried different particles to put into the milk
to see if the holes are growing again.
Hay powder is the best one, and we really could see that
the hole formation was dependent on
the concentration of the hay powder we put in it.
It's only one milligram per thousand liters.
- Modern food safety standards mean that
milk is far cleaner now than it ever was in the past,
without the tiny... well, these days, it's "imperfections".
In the past, it would have been contaminants,
but, without those, if the milk is perfectly clean,
the holes just don't form,
and while those holes don't really affect the taste,
they certainly affect
whether Swiss cheese looks like Swiss cheese.