General Sustainability/environmental Tea

Would you like plastic in that?

Straws with viscous liquid (milkshake) in them
Do you need that straw?

Plastic Free July starts in just a few days time. Each year this initiative encourages us to eliminate, or at least reduce, our use of single use plastic throughout the month of July. It is a great way to increase our awareness of our plastic use by attempting not to use any.

There are numerous reasons that we may want to reduce our plastic consumption. In addition to the problems of litter associated with plastic waste, there are problems for wildlife caused by ingesting our rubbish. Even if we dispose of it responsibly, plastic takes a long time to degrade. It is thought provoking to consider that the take-away cup that we discarded yesterday may still be lying in some landfill site years after we have forgotten about drinking that coffee. So what can be done about it and what are the specific issues for coffee drinkers?

air valve, plastic, environmental coffee packaging
Air valves and metallised plastic are common packaging materials for freshly roasted coffee, but can we avoid them?

One way to start to reduce our dependence on single use plastic is to understand how much we actually use on a day by day basis. Registering for a plastic free July is one way of doing this. As a result of attempting a Plastic Free July last year, I have found some plastic-free habits that have stuck with me all year. Loose leaf tea is one such improvement (teabags can also contain plastic). Although initially it seemed a bit of a pain to use a basket to brew the tea, as I kept with the habit I found it easy to compost the tea leaves after making a brew and the tea tastes better too. Things like shampoo bars and tooth ‘paste’ tablets (from Lush) have also been better and longer lasting than similar products packaged in plastic bottles.  Although some plastic habits are hard to break, living as plastic free as possible for one month did deepen my awareness of the plastic that I take for granted.

But perhaps living plastic free for a month is too daunting? An alternative challenge sadly emphasises just how linked coffee drinking can be to single-use plastic consumption. The Top 4 challenge asks you to eliminate, just for July, the target take-away items. Of these 4, at least 2 (and arguably 3) are linked to coffee drinking or cafés. The top 4 are plastic bags, bottles, take-away coffee cups and straws. Could you avoid these for just one month? Take the challenge.

blue tits, mint water, mint infusion, mint leaves in water
Enjoying a glass of water in a cafe can be better than running with a bottle of water anyway.

If you are ready to go plastic-free in your coffee habits, here’s a list of where we frequently encounter single-use plastic while drinking in cafés or even at home, together with suggestions of how to avoid the plastic where appropriate. Please let me know in the comments section below if you can think of further examples (and how you are avoiding them either in July or more permanently).

  • Disposable take-away coffee cups – get and use a re-usable one. You can find a helpful comparison of different types of re-usable coffee cups on Brian’s Coffee Spot.
  • Tea bags – yes they can contain plastic, see more information here. To avoid them, get hold of a metal tea basket, or even a tea pot and strainer and start investigating loose leaf tea.
  • Water bottles/soft drinks bottles – if in a café, why not enjoy the moment by staying with a glass of water rather than grabbing a bottle? If you are in a hurry though, a flask (such as klean-kanteen) is a great investment. In some parts of London (and perhaps elsewhere?) chilled tap water is available on tap for use in re-usable bottles
  • Air valves on your roasted coffee bag – do you really need these? The Nottingham based coffee roaster, Roasting House, did a taste test on freshly roasted coffee packaged with and without air valves, you can read their results here. If the coffee roaster that you normally purchase coffee from insists on using air-valves, why not write to them to request that they reconsider their packaging or try a more environmentally conscious roasting company to see how their coffee compares?
  • Coffee packaging – What type of material did the last bag of coffee that you purchased come in? Chances are it was metallised plastic, why not find a roaster with alternative packaging? Who knows, you may find another great coffee roaster to add to the ones that you buy from.
  • Straws – why would you use these anyway?
  • Milk bottles – Some companies still supply milk in glass bottles, otherwise you could consider non-dairy milks that can be home-made such as oat or almond. Some cafés also offer home-made non-dairy milks which would be a way of going plastic free while enjoying a latte in a café.
  • Cakes/sandwiches packaging – in larger chains these may come in packaging. However, if they are coming in packaging then they are not likely to be that fresh, find somewhere else with better cakes or sandwiches or make your own!
  • Spoons/cutlery
  • Packaging for sugar etc – ditching the sugar is supposed to be good for you anyway. If you cannot resist sweetening your coffee, try to find a sugar that is packaged in paper rather than plastic.
  • Washing up liquid – switching to a re-fillable washing up liquid reduces (but does not eliminate entirely) plastic waste.

Good luck if you take the challenge. There are still a few days left to plan how you can reduce the plastic in your life before the start of Plastic Free July 2017. Please do let me know how your attempts to be plastic free go and whether you find, as I did last year, that you enjoy your tea (or even coffee) more when you do so.



Allergy friendly cafe with good nut knowledge Coffee review Home experiments Observations Science history

Bend it like sugar at Muni, Fulham Road

Muni Coffee, near Chelsea and Westminster hospital
Muni Coffee on Fulham Road

The area around Fulham Road and Chelsea & Westminster hospital is one that has long been fairly empty of speciality coffee establishments. Then, in June this year, Muni opened up on Fulham Road (just over 200 m from the main entrance of the hospital, in case you are visiting and looking for a good café nearby). Muni’s website emphasises its social mission, knowing the farmers they trade with by name and introducing Filipino coffee to the UK. Inside, there are plenty of tables (with more outside if you are visiting in warmer times). There is a menu on the wall behind the counter to your right as you enter, but I missed the listing of the Pandan iced tea (which would have been very interesting to try) as I was obviously not paying enough attention and instead opted for my default trying-a-new-cafe coffee, a black Americano.

My sometimes companion in these reviews had a soya hot chocolate while I was very confident to enjoy one of the (lovely) salted caramel brownies because Muni lists all the ingredients for all of their cakes on a tablet device at the counter and so I was encouraged to double-check the ingredients list to see that there was nothing vaguely nut-related in it. A very good feature and this cafe definitely gets a tick in the “cafes with good nut knowledge” category on the right (as well as the new allergy-friendly category). As mentioned, the coffee is imported directly from the farmers in the Philippines, and roasted by Muni in North London. The black Americano I tried was fruity and flavoursome, while the beans I purchased and prepared later using a V60 produced a sweet and floral brew, perhaps with blueberry notes (but with no tasting notes on the packet, I’d be interested to see if others agree with me on this, please let me know in the comments section below).

coffee cake Muni
Coffee and nut-free salted caramel brownie at Muni

On the ceiling, wooden beams had cracked and aged creating a lovely aesthetic and taking me on a thought trail that involved aeroplane engines and heat process treatments. But then I noticed something else. As it was getting dark, the cars passing by on the busy Fulham Road were mostly using their headlights and this meant that, every so often, the edges of the windows around the door changed these headlights into a spectrum of colour. Flashes of blue, red and green as each car passed. It reminded me of Newton’s experiments in which he used a prism to first separate sunlight into its various colours before recombining it with another prism into white light. An effect that led me to think about an instrument that has been advertised as a tool to creating better coffee: the coffee refractometer.

Some of the same physics links Newton’s prism with the coffee refractometer. Perhaps you remember “Snell’s law” from school. The equation describes how much deviation light experiences as it passes from one medium (air) to another medium (glass or coffee). Light travels at different speeds through different media and the refractive index can be thought of as an indicator of the degree to which each medium slows down the light.

the door at Muni
The window at the side of the door at Muni. Rainbows of colour were produced by the headlights of cars as they went by.

For the prism, the important detail is that light is composed of many colours (which means in this context, many wavelengths) and not all wavelengths are slowed to the same degree. This means that the refractive index of the glass prism is slightly different for red light than it is for blue. Consequently, the spectrum opens up as the white light travels through the prism.

For the coffee refractometer, the important point is slightly different. Water containing dissolved solids has a slightly different refractive index than pure water. Measuring the deviation of a light beam through a drop of coffee therefore gives an idea of the concentration of “total dissolved solids” and so a guide to the extraction of coffee from the grind that you have achieved. The difference in refractive index is however quite small, if the measurements here can be relied upon, while water has a refractive index of 1.333 (at 20ºC), a well extracted coffee showed a refractive index of 1.335. We can calculate how much difference this makes to the angle that the light is deflected: Assuming light enters the drop at an angle of 30º, the angle that light is refracted in water is 22.03º, while in the coffee it is 22.00º. A small effect that would be quite difficult to measure unless you had a refractometer.

However, there is an ingredient in some people’s coffee that bends light enormously: sugar (though I do hope that no one reading this uses it in the quantities needed for the experiment below). The refractive index of water is very dependent on the total concentration of dissolved sugar it contains. Therefore you can do a really cool experiment in which a sugar solution (which has more concentrated sugar at the bottom than the top) can be seen to bend the path of a laser beam. All the equipment can be easily found at home (or purchased for not too much from hardware/office equipment shops). Let me know if you try the experiment how you get along (and if you decide to try using a refractometer to enhance your coffee brewing experience). The video was shared on youtube by the Amateur Astronomical Spectroscopy group (CAOS).

Muni coffee is at 166 Fulham Road, SW10 9PR. Just around the corner on Drayton Gardens, is the blue plaque for Rosalind Franklin who used to live at an address there.


General Science history

A link between high blood pressure and drinking cold brew through a straw

Straws with viscous liquid (milkshake) in them
Drinking milkshake through a straw or two.

How do you drink your cold-brew? How about iced-coffee or iced-tea? Would you drink it through a straw? Maybe a smoothie or a milkshake would be ok. Perhaps you’ve noticed that you need a large straw to drink that milkshake while a small straw works for ‘thinner’ drinks. But what is the connection between this and the measurement of your blood pressure? It is not that drinking coffee gives you high blood pressure or the reverse. That question can be left for discussion on other websites. No, the question is, can drinking a milkshake through a straw give you an insight into the problems of high blood pressure caused by the build up of cholesterol?

If you are currently in a café, why not try an experiment. Get two straws and try drinking a cold drink using both of them together. It’s tricky but it is do-able, you can drink your drink. Now place one straw such that it is ‘sucking’ on the air outside the glass with the other straw still in the drink. Without cheating you can no longer ‘suck’ up that cold brew. Plugging either end of the ‘free to air’ straw enables you once again to drink your coffee. This experiment demonstrates that you are not really ‘sucking’ the liquid through the straw, rather you are generating a pressure difference between the top of the straw (a lower pressure in your mouth) and atmospheric pressure (higher pressure, around the drink) that pushes the liquid through the straw. Attempting to drink through two straws when one is open to the atmosphere cancels out that pressure difference.

2 straws
The straw on the left has a diameter of 3mm, on the right, 6mm.

Now another experiment. How do straws of different diameters affect the amount of liquid you can ‘pull’ through the straw? Try it. I have two straws in this picture, the smaller one has a diameter of 3mm, the larger one a diameter of 6mm. It takes a lot longer to drink a quantity of liquid through the smaller straw than it does the larger straw (assuming that you are drinking the same drink with each straw). For example, I drank 200ml of water in 10-12 sec with the larger straw but 26 sec with the smaller straw.

Back in the early nineteenth century two people were each investigating how liquid flowed through narrow tubes. Jean Leonard Marie Poiseuille (1797-1869) was investigating tubes of diameter 0.013-0.65mm in order to understand the flow of blood through capillaries in the body. Gotthilf Heinrich Ludwig Hagen (1797-1884) was investigating tubes between 2.3-6mm diameter (the same as the straws in the picture). Although they came to their conclusions independently, their work now forms the basis of parts of our understanding of the circulation of blood in the body†. What is now known as the Hagen-Poiseuille law states that the flow of liquid through the straw (or blood vessel) is proportional to the pressure difference between the two ends of the straw (how much you ‘suck’ so to speak) and the radius of the straw raised to the fourth power*. That is, it is the radius x radius x radius x radius. Doubling the radius of the straw results in a 2x2x2x2 (= 16) increase in flow rate.

Experimenting with the two straws does not give you quite the 16x difference that you may expect from this law perhaps partly because the flow into the straw is turbulent. If you maintained a uniform flow through the straws, you should find that the difference in flow rate between the two straws would be closer to 16x.

straw, water, glass, refraction
A straw in water, another physics-phenomenon that is worth contemplating for a while.

Of course, what applies to straws applies equally well to arteries or even the alveoli in your lungs. If your arteries get clogged by too much cholesterol, the reduction in the diameter of the artery leads to a reduced flow of the blood. A decrease in the diameter of an artery by just twenty percent more than halves the flow rate of blood through it (thereby increasing the blood pressure required to maintain ‘normal’ flow rate). Similarly the constriction of the alveoli in the lungs of asthmatics reduces the flow rate of air through the lungs in an asthma attack.

So it is not quite the fact that drinking cold-brew through a thin straw can give you high blood pressure. It is rather that thinking about how liquid moves through straws can help you to think about what is going on in your body. Those arteries of yours may be worth thinking about as you sip your cold brew this summer, whether or not you do so through a straw.


*The Hagen-Poiseuille law states that the flow rate F = ΔP.(r²)²/(8ηl) where ΔP is the pressure difference, r the radius of the straw, η is the viscosity of the liquid and l the length of the straw (or artery). Perhaps you can see why you will need a larger diameter straw to drink a milkshake.

†Blood Pressure Measurement, An Illustrated History by NH. Naqvi and MD Blaufox, Parthenon Publishing (1998)