Water

Here is a .PDF version of the water stuff I did so its easier to read and you don't have to scroll up and down blogspot to read it...

water!

h20 : part 3 of 3

Reverse Osmosis (RO)

Now that we have out minds wrapped around Ion-Exchange we can move onto the other major way mineral and/or dissolved solids are removed from water: Reverse Osmosis (RO). To best understand this process lets break down water into two components: solute and solvent. The solute is everything other than h2o, all of the dissolved (and particulate) solids. The solvent is the water in its pure form. A reverse osmosis system is made up of six main components: a pump, a taste and odor micron filter, system membrane(s), mineral cartridge (calcite), post scale inhibitor filter, and a storage tank. To understand this process best we'll focus on the membranes as they are the component that does the removing, or more accurately, the separation of the solute from the solvent. Reverse osmosis at its core is based on a pretty basic principle in chemistry that we touched on earlier. It is the tendency towards balance at the molecular level. In our previous example as it relates to ion-exchange we talked about positively and negatively charged ions. In the natural process of osmosis when two liquids that contain a different amount of solute (or TDS) are separated by a permeable membrane, there is a tendency for the lower solute liquid to move towards the higher solute liquid to achieve a balance of solute concentration. This tendency in our case is referred to as osmotic pressure. During reverse osmosis pressure is increased (via an external pump) to reverse this process and separate the high-solute liquid from the solvent. The high pressure is very important as only under the higher pressures can the chemical process separating the solvent occur in reverse. When we brew espresso we are brewing at about 9 bar of pressure. When you lose the pressure, you can no longer emulsify the oils from the coffee and you lose flavor, crema and really, you lose what we define as espresso. Now, RO is really nothing like that, but it does require high pressure to accomplish the goal, 17 bar to be specific. 250psi of pressure force the water into the membranes. The membrane is best pictured as the front page of a newspaper wrapped up very tightly: multiple layers in a circular/spiral pattern. The membranes are designed such that there is only one-way movement from the high-pressure/high solute side to the other side: low pressure/low solute. Under these circumstances the ions (mineral, sodium and otherwise) are removed and only the h2o molecules pass through the membrane. The high-solute water is directed or washed out of the membranes as waste water and the filtered water which is now almost or at 0 TDS comes out the other side of the membrane. Since the water exiting the membranes is so aggressive it is routed through a cartridge much like the bowl style calcite cartridge we talked about earlier. This 'remineralizes' the water and 'stabilizes' it for use. In some systems it is then run through a scale inhibiting filter before hitting the equipment. The inherent problem we are faced with, however, is that water goes into the membranes at a very high pressure but comes out at an extremely low pressure and flow rate. There are many sizes of systems and in general, the larger the membrane the higher the output flow-rate and pressure will be, but it can range from a drip/trickle to garden hose half turned on type flow-rate and pressure. From here on out I'll use flow rate and pressure as one in the same even through liquid science dorks would really criticize me, the normal people out there like me need to take it one concept at a time.  Since the output is so little we are faced with a problem. Our coffee brewers need at least 20psi to operate. And we need minimum flow rates and stable pressures to brew espresso too. With an RO system you'll see a small to rather large tank down-line from the rest of the system. About half or more of the tank is taken up by a large inflatable bladder. It is kind of like a bike tire. A bladder inside is pressurized to keep a certain amount of resistance against the tire material. Since water cannot be compressed it meets the resistance of the bladder inside the tank which compresses to then apply pressure to the water tank. With a large enough bladder and volume of water, stable pressures can be achieved. RO systems are very effective at taking care of water chemistry problems. However, the main concern on my end is two-fold. One, there is an amazing amount of water waste involved in most RO systems. Two, stability in dynamic water pressure and flow is pretty tough unless the system is very large in comparison to your needs.

Water waste is an inherent reality in the use of an RO system to filter your water. The discharge water that is highly charged with the solute is routed to a drain. Unfortunately the efficiency can be as low as 15%. For example, of the 100 liters of water that the system receives only up to 15 liters makes it through to the storage tank while 85 liters goes down the drain. Now, large commercial systems can achieve efficiencies higher than this, but we still see a lot of waste during RO. This is a problem. I'm sure someone could probably come up with a good use for the waste water and reroute it for storage. Or use it for the toilet flushing, garden watering or better, but I can't say I've ever seen anyone with an RO system doing that.

Stability in espresso brewing pressure has been a major focus in the specialty coffee industry. Dialing in multiple pump pressures, flow restrictors, and valves to give the barista ultimate control over brew pressure has been a realization (I posted here) in the espresso machine world. Honestly, the most stable brewing systems would be a result of the machine drawing filtered (RO or whatever) water from a water tank at 0 pressure (think trade-show set ups). In an RO system you are completely at the mercy of the holding tank and the pressure it can give you. If your usage out-paces the systems' ability to process water then you will quickly run into erratic pressures. This can be fixed with larger membranes and larger storage tanks, but is a real problem with many of the systems marketed to espresso professionals.

Some of my opinion towards RO systems has to do (unfairly) with never really seeing them work well consistently. Whether it is the user's fault for not changing membranes on a regular basis, the system being under-sized for the demand, or water not being properly pre-treated to make the system works properly, I haven't seen great performance. Based on my experience, even Starbucks has more problems with the water system (RO) then the rest of their coffee equipment combined. As users meet these issues, costs get pretty big. Storage tanks are made out of special materials to handle aggressive water, membranes are expensive and in larger systems, a pain to change. With all of the cost and maintenance involved to keep the system up and running it does offer nice water. But again, the user needs to make sure the PH and Chloride levels are okay for usage as well. Bonus: Most RO systems should use softened water instead of hard water. The membranes will last longer removing the sodium ions from soft water than the mineral ions from hard water. Also, a pre-filter that takes water down to .5micron clean will help the membranes last longer.

pH, Chlorides

Aside from the TDS and filtration tactics that we've already covered there are two other aspects that are very important to look at in regards to your brew water. If you refer back to the comparison of Madison to Seattle water you'll see that a lot of the compounds listed are dissolved substances in the water. There are a couple though that are more a reference to the molecular side effects of the various things that have been dissolved into or taken out of the water due to the water source and/or the filtration system: Chlorides and pH Level.

The presence of chlorides in water will (over the long term) cause metal to corrode. It is a little different than aggressive or low TDS water breaking metal down due to its solvent nature. Corrosion is a chemical reaction that starts to pit the metal. Eventually you will get a pin-hole leak at a weak point, usually at a weld, and then a leak. RO systems are effective at removing chlorides as are many ion-exchange processes.

pH is the measurement of how acidic or alkaline a liquid is. Water (pure water) is considered neutral with a pH level of 7. Specifically, pH is a reference to the concentration of hydrogen in the liquid. The lower the pH the more acidic it is. In water, the pH level changes based on the various chemical processes (both natural and employed by filtration systems) it is exposed to. pH level is one predictor for how the water will react when in contact with other substances. Since we run water through all sorts of metallic and plastic materials inside of coffee brewing equipment, not to mention that we soak ground coffee in it, pH is an important number to consider. Generally, water should be within 1pH of 7 or neutral. Since some of the ion exchange processes load hydrogen into the water it is important to know the pH of your water.

Final Thoughts

At this point you're probably thinking you'll never boil another gram of water again. You could always cold-brew everything and just forget about it (did you also forget that water has to be hot to brew good coffee? can't do it with cold water), but where's the fun in that? Hopefully, you know a little more about what water does when heated and what will happen if certain levels of dissolved solids are too high or too low. The first thing you should do is taste your water. Don't drink it, taste it. Seriously. Go pick up a gallon of distilled water and do a tasting against your tap water, both at room temperature. Distilled water is at 0 TDS and you will taste the difference right away. The second thing you should do is test your water. Test the water before it goes through any kind of filter and test the water where it hits your brewing equipment. Most Universities will even do it for free or minimal cost as part of the lab services. Armed with the knowledge of what is and isn't in your water, you can start to figure out what it is you should do. RO is definitely a great way of cleaning and grooming your water for good coffee brewing but it tends to be expensive, require regular maintenance, and you need to be careful of the calcite cartridge and what specifically is going back into the water. Ion-exchange is also effective and I like the idea of not having to waste water to get water. But, again make sure you know the effect the ion-exchange is going to have on the other attributes of the water. Also, CHANGE YOUR FILTERS. That sounds obvious, but whether you are going with RO, Ion-Exchange cartridges or tanks, coarse filtration and carbon you need to change the filters, cartridges,membranes or substances etc. involved in the process. Test your water on a regular basis so you know what is happening and when. In the end the list below is a good 'recipe' to go with; in my opinion it is a water that will boil and heat nicely and not break your equipment down while brewing fantastic coffee.

TDS = 50-200ppm

Hardness = 3-5grains

Chlorides = 0

Chlorine/Iron or other taste/odor causing agents = 0

pH = 6-8

If I had my way I'd set up a few filtration systems up on both batch brewing and espresso machines to taste specific TDS and mineral levels and the difference each has on the respective brewed cup of coffee or espresso. I also think it would be fun to cup one coffee with varying amounts of TDS from 0 up to RO waste water (never tested it but very hi ppm I'm sure). It would be such a great lesson in TDS's effect on coffee flavor. Use the same coffee, brew form and brew recipe and just vary the water used. Any way you look at it, water chemistry is probably the most important variable in the extraction of coffee. I'll end by stating a few of my untested assumptions and anecdotal thoughts that, whether true or not, demand that we give just as much thought to our water system as we do our coffee roaster, espresso machine, and brewing system.

The lower the level of TDS the more we can taste inconsistencies and problems with grind, dose and water-temp.

Brewing with low levels of TDS will cause the acidity of the coffee to overpower other attributes.

Generally, brew times can be faster with lower levels of TDS in water.

With water at 50-200ppm levels of TDS it is easier to brew a balanced (body/acidity/flavor) cup.

Softened water and high (+200) levels of TDS in water brew a masked version of what the coffee could be. Its like looking at the world through fogged glass.

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.

Pre-Filters

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.           

Carbon

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-19^th 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...