30 April, 2012

h2o: pt. 2

Almost a year since water part 1....been busy!  But, I've learned a ton as well.  Here is part 2:

Ok. So now that we know a thing or two about what is in our water aside from 2 hydrogen atoms and 1 oxygen atom, we can move on to figuring out what to do about it. We also know why we need to do something about it...but lets review that one for a sec:

**Most importantly #1...TDS levels will affect how the coffee tastes. The higher the TDS level the less 'aggressive' the water is.  Very aggressive water (low TDS) will extract a lot (more than we want?) from the coffee and higher TDS water will tend to extract less effectively.  Also, aside from minerals, there are other compounds dissolved in water that have flavor. You want to taste the coffee, not these compounds.

#2...It will affect how your equipment runs (or doesn't run!). When heated, the dissolved minerals in the water will turn from a liquid, back into a solid. This can affect how quickly or efficiently the water can flow through the machine. It will begin to effect the quality of your extraction before you even have a breakdown. It is akin to a person having a heart attack...flow is restricted and eventually stopped. Manufacturers spend a lot of time and engineering brain-power figuring out the desired flow rates so that the machine performs to specifications. For example, Synesso knows that water flows through the pre-heater at a certain rate and hits the coffee boilers at a specific range of temperature based on this knowledge. Baristas and technicians are swapping out gicleurs (flow restrictors) in .1mm increments to slow down or speed up flowrates and meter out pressure increases...mineral build up in the right (or wrong) place will do the same thing. What you end up with is unpredictable performance and eventually no performance.  Then, no coffee.  

Here is a picture of a water level probe with some minor build up...if left uncleaned eventually it will fail to signal the auto-fill system that the boiler is full of water.  Boiler overfills, you can't steam milk.

#3...Remember how we talked about coffee being a solvent? Very low TDS water (aggressive) is a 'stronger' solvent. So, low TDS water will actually break down and remove compounds from your equipment. Boilers are welded components in your coffee machine(s), usually made out of stainless steel or copper. Aggressive water will start to pit or damage these boilers and eventually make a small pin hole that will develop into a full blown leak after awhile. You don't want to have to replace your boiler...trust me. Spend that money on sourcing better equipment and better coffee.  Here is another example:

In a Fetco Coffee Brewer (not the ECO series) the hot water tap receives water supply via a pick up        tube that has an outlet at the bottom portion of the water tank.  There are brass fittings that construct the elbow on the interior of the brewer.  The thing about a coffee brewer boiler is that it isn't a constant water temp from bottom to top.  The water temperature nearer the heating element flange and tip of the thermal probe is at the set point (+/- 200F) but the water at the bottom of the tank is nearer to about 90F depending on your incoming water supply temperature.  If the water supply to the hot water spout is coming from the bottom of the tank then your hot water won't be so hot.  In the picture you can see the erosion of the brass elbow fitting. 

The water supply (in this case around 50TDS) wore a hole in the bottom of the fitting (pic. 3) and eventually the entire elbow and pick up tube assembly fell apart.  Symptom: Water temp for coffee is fine, hot water spout cold.  This was all due to the aggressive nature of the water.  On top of that, Fetco located the water supply to the tank just beneath this elbow fitting so the velocity of the cold water hitting the bottom of the fitting probably didn't help but, to be fair, this breakdown was probably a year or two in the making.     

**Writer's bias:  I tend to use examples from manufacturers that, in my opinion, design equipment that does a great job even when/if you don't have the perfect water.  Certainly, manufacturers can sit comfortably on the claim that you, the user, should be doing right by your water to uphold the specs and claims of any manufacturer and the associated warranty but with that said, some manufacturers do better than others when it comes to designing a piece of equipment that is somewhat 'resistant' or 'tolerant' of bad water.

Now that we have reviewed the WHY, lets talk about the HOW...

What Do We Do Now?

There are many, many, many ways water is treated to keep it nice. I'm not a scientist so I'll generalize by saying there are two ways to treat water. Take stuff out or put stuff in, or a combination of both...with the end goal being a water chemistry that will play nice with your coffee and not deposit solidified minerals inside your equipment.

If I had a shop with any kind of water using equipment I would use a pre-filter as my first line of defense. A pre-filter is usually a bowl-style filter where the water is forced through a tightly wound coil or solid core fiber material to remove particulates larger than around 5-25 microns.  This will do nothing for dissolved compounds, but when you remove particulates from your water you will save more expensive filtration down the line from getting clogged up.  This is especially important in areas where there are alot of old city pipes or construction projects going on.           

Using carbon to filter water is probably the oldest form of filtration and may have origins in Egyptian engineering and certainly hundreds of years with documented active use starting in the mid-19th century. It is effective at removing compounds that effect the taste and odor of water. This happens through a cool scientific process called adsorption. Not to be confused with aBsorption, aDsorption is a chemical process by which some of these dissolved substances have the tendency to 'stick' or adhere to the carbon molecules. This helps a lot with the various dissolved substances in water that effect the taste and odor of the water, but does little for the hardness (or mineral content) of water. It is important to understand that the carbon does not deposit anything in the water to help, it only removes to help with water chemistry.  Like many things, I wish I could travel back in time to see how this was discovered because its origins really baffle me.

Ion Exchange: Softener
Ion Exchange is probably the most commonly used form of water filtration.  There are many point of use and cartridge style filters that apply a science of ion exchange to take care of water problems.  To best understand the concept of adding something to your water to chemically change it and avoid mineral problems we can look to a water softener as a fine example. In Madison, WI everyone has a water softener in their basement. Most probably don't understand the science of it, but know that if the salt isn't added their soap doesn't work very well, Packer-branded pint glasses look cloudy, and the hot water heater will eventually breakdown. The basics process of softening science is this: trade something for the minerals. Put something into the water to get the mineral out of the water. This process is called Ion Exchange and is applied both in softener systems and cartridge style filters at the point of use. Here is how it works:

In an atom or molecule (the things that make up every substance we know) there are electrons and protons...high-school stuff right? An ion is an atom where there aren't an equal number of these electrons and protons. This gives the ion an inherent positive or negative charge. In water,  the minerals carry a positive charge. Well, these positive charged ions want to bond with their antithesis, a negative charge to achieve balance. When the water is in contact with a negatively charged substance then the minerals want to leave the water molecule and hang out with the negatively charged element. In a softener the big scuba-diver-looking tank is filled with little hard plastic beads made out of polystyrene, a substance that carries a negative charge, but have been washed with a concentrated sodium solution (salt water, from the salt bin). The sodium solution is also positively charged so sodium ions attach to the polystyrene. When the water passes through the bead tank it trades the mineral ions for a huge supply of sodium ions that had attached to the polystyrene. So in goes hard, mineral rich water and out comes soft sodium-ion rich water. The sodium ions far outnumber the mineral ions so your TDS actually goes up even though you are losing the minerals. After awhile the little beads are quenched and don't want any more mineral. The softener automatically regenerates. During this process the salt water (rich in sodium-ions) is cycled through the polystyrene tank and out to a drain. Since the sodium ions far outnumber the mineral ions the polystyrene gives up the mineral ions in exchange for the sodium and the tank is once again ready for a fresh batch of hard water to exchange all over again.

Softening your water is a great way to remove mineral.  The only problem is that there are so many sodium ions in the water that it brews terrible coffee.  The mineral is gone and that will help with equipment but the water is so saturated that the coffee you would brew with it would come out flat, boring, and to some pallets, salty.  Despite this, many people still use softened water for their espresso machine.  Since the variables of water temperature and pressure have such a dramatic effect on flavor the water chemistry isn't as concerning, as long as the equipment runs.  I'll agree that water chemistry has less of an effect on the flavor of espresso than in any other brew form, but I don't think that is a justification for using softened water at the espresso machine.

Ion-Exchange: Cartridges
The science of ion-exchange is used in many other ways outside of a water softener that uses salt and trades sodium for mineral ions.  There are alot of cartridges that employ this same science and use substances other than salt to trade ions, too many to really go into with much detail. In general, my opinion of cartridges depends entirely on the amount of mineral found in your water supply.  Here in Madison cartridges are almost completely worthless for the management of minerals from a cost perspective.  First, you can't recharge the ion trade substance after it is saturated so it is a throw-away product.  Second, the water in this area is so hard that the cartridge will be spent in a very short period of time.  Many of these cartridges cost more than $100 per unit and with having to change it every 2-3 months gets prohibitively expensive.  Further, with many cartridges you just don't get very quality water, and end up with a similar problem as salt based ion exchange systems, high TDS (though low mineral).  You also end up with coffee that misses its potential.

Remember back in Water Part I when we talked about how water hardness is measured in grains (per gallon) of hardness?  Ok, in Madison we are looking at about 25 grains of hardness and Seattle around 1.5 grains.  Madison has very hard water.  In general, cartridges will probably suit your needs if water is hanging around >7 grains (and depending on what else is in your water) but when you start going over that then you'll be spending a huge amount of cash on water filters.  Why they cost so much (and shouldn't?) is another story, but they do.  Most filter manufacturers will post capacity estimates on the cartridges and use a 10grain water hardness as an average.  People heating water in Madison need to divide that number by approx. 3 to come up with an accurate filter-change frequency.

Ion-Exchange: Proprietary 
If you've ruled cartridge style filtration out of the list of options then you need to turn towards either another ion-exchange option or reverse osmosis.  Here in Madison I've learned about an interesting system called Carbox from Culligan.  Now, I'm still getting my mind wrapped around this, but it seems to be a pretty cool system after some initial tweeks.  Think softener, only instead of salt (sodium ions) we are looking at a substance called Carboxylic Acid.  Without getting too chemisty-y, simply put, this compound trades hydrogen ions for the mineral ions in the water.  You end up with low mineral water (it removes about 90%) that drops the extra hydrogen ions leaving water that is low in hardness and around 50TDS.  After the ion-exchange the water runs through a carbon filter to remove taste and odor issues.  Since the water is still very low in TDS it goes through a mineral (calcite) cartridge to bring it back up to 'normal' levels.  The problem is that the calcite cartridge isn't metered.  The longer the water is in contact with the cartridge the higher TDS.  In applications where the system is feeding an espresso machine only, a situation where you have very small amounts of water used at intermittent times, the water hardness can spike too high again.  An idea suggested by Synesso was to dump the calcite cartridge altogether and just bypass hard water (pre-carbon filter) back into the low TDS water.  A great idea since the water chemistry is relatively stable and predictable.  What we end up with is water that is metered up to about 5 grains hardness with a TDS of about 130.  For applications that are drawing water in higher volumes  like batch-coffee brewing, it was less of an issue since contact times with the calcite were less and it seemed that if you pulled at least a liter (or the volume of water housed in the calcite bowl when the system is static) then hardness and TDS level remained pretty consistent.  Still, I ike the idea of control as opposed to an uncontrolled system.  In the end the ideal system was the one that employed the hard water bypass to be able to limit/control hardness and TDS levels.

Water Is More Than Minerals and TDS
You are right, alot more.  We need to be concerned about what the system we choose does to the overall PH and Chloride levels, but lets leave that for just now and talk about the last way that many people deal with their mineral rich water: Reverse Osmosis.

Reverse Osmosis
Coming Soon...        



1 comment:

  1. I love that you not only have the practical knowledge behind WHY the machines break, but you also have all this amazing science too. Great stuff.