Some cold brew coffee drinkers, really love it but don’t drink all that much due to caffeine or other reasons.  But we all want it to taste great and all have tasted stale, oxidized or even sour flavors in old coffee.  How can one maximize the life of the coffee and then how long will it last?

Normal cold brew coffee will stay good longer than hot coffee which has cooled.  Oxidation occurs much more readily in hot water than in cold.  Hot coffee has more acids and tannins in it than cold brew.  They start to degrade shortly after the coffee is made, and often the coffee has noticeable oxidation in a short as a half hour.  The oils in coffee soluble can oxidize more quickly at elevated temperatures, causing coffee to taste sour. Acids also degrade, the most notable of which is chlorogenic acid into Quinic  acid and caffeic acid, causing coffee to taste bitter. 

Cold brew also will oxidize, but it takes much longer.  Even in a cup, it will still be drinkable the next day if kept in the refrigerator.  If you keep it in a sealed container like a jar, bottle or growler, you should be able to get two to three days before you notice a taste change.  If the cold brew is concentrated and you dilute it at the time of serving, you will get a week out of it.

The real “shelf-life” lengthener is Nitrogen.  Food distributors have known that for a long time.  Lettuce is harvested in the Salinas Valley of California, put into refrigerated containers, filled with Nitrogen, and sealed in the late Spring and Summer.  That same lettuce is then shipped to Japan and Europe and the containers are opened up the next winter.

Even the simple act of using a disposable Nitrogen wine preserving can will double your shelf life to two weeks at least.  Those who make Nitro cold brew or even just keep their coffee under Nitrogen should get at least a month out of their coffee if kept cold.  I’ve found that cold brewed Nitro coffees don’t even reach their peak flavor for at least 24 hours after they’re put into kegs.  And it’s not just the Nitrogenating part.

We’ve tried kegs of cold brew that were a month old, and couldn’t tell a difference from when they were freshly made.  But in order to do that, one has to minimize oxygen exposure every step of the way.  We put a small layer of Argon on top of our brewing vessel.  And we make sure our keg is purged with Nitrogen before adding the coffee.  Coffee Love in Los Angeles even nitrogenates their brewing water and tries to drive out much of the free Oxygen in the water.

For those roasters who can, make sure the canning line fills the cans completely and that you micro dose the coffee with liquid Nitrogen just before the lid goes on.  Of course you have to observe all local and USDA health department rules.  But often the listed shelf life is two to three months if the coffee is kept cold.  I once opened a can of Los Angeles’s B Sweet Nitro Cold Brew, it still was tasty at 15 months old.

That may be the single most common problem we hear about.  Either the coffee just stops or starts trickling out of the faucet.  Fortunately, it usually just involves a fairly easy fix of some kind or another.  Rather than go though a list of problems than talk about the fixes—I’ll just go through what we do when we encounter the problem.

 

1. Make sure there is Nitrogen to the keg.  Just pull the pressure relief valve a bit on the lid of a ball lock keg or disconnect and pull the handle down on a sanke coupler.  Also look at the gauges on the Nitrogen tank.  The top gauge should be above 30 psi and the left gauge above 100 psi.  The shut off on the regulator should be down facing the line.  All this tells you if Nitrogen is going into the keg.
2. Clean the disk diffuser holes inside the stout faucet nozzle.  DISCONNECT THE KEG FIRST.  You can just unscrew the nozzle, tap it on a hard surface, and the disk diffuser should fall out of the nozzle.  That’s the thin ‘not quite dime sized” screen with 5 or so tiny holes.  Coffee grounds tend to clog those holes blocking off the flow.  Just rinse it and put it back.  Be careful, it is small and can get lost easily.  Make sure you put back the white regulator core and any o-ring that may fall out.
3. Make sure the keg isn’t too cold.  We’ve seen frozen coffee inside the keg dip tube even when the coffee itself isn’t frozen.
4. Finally, sometimes the grounds clog the keg dip tube.  The easiest way to clear them is to release some pressure from the keg.  Turn off the Nitrogen, and put the black “out” keg coupler on the Nitrogen hose where the grey “in” coupler was.  Then turn on the Nitrogen (FIRST) and hook it up to the “out” fitting on the keg.  That should push Nitrogen into your keg through the dip tube and remove the grounds.  Then reverse what you did and put the grey connector on the Nitrogen line and the black connector on the coffee line.  Never do step 4 with an empty or “off” Nitrogen, you’ll get coffee backing up into your nitrogen line.  Step 4 only works with a ball lock keg—you’d have to take the sanke coupler apart to do it with a sanke keg.

If you do have grounds in your keg, you may be repeating the repair.  Or you could pour from one keg to another with a funnel and filter.  That’s not the best option for fresh coffee—you don’t really want to expose it to air more than necessary.  Of course, the best solution is to be careful when you filter it, but you already know that.

This is a question we hear all the time at Tavern Service.  Roasters and coffee shops want to know how much Nitrogen they will use when pouring and nitrogenating coffee.

Of course that depends.  What size is the nitrogen tank?  What is the volume of coffee being served?  What nitrogen pressure does the roaster want the coffee dispensed at in order to get the optimal head?  For the sake of this article, I’ll assume the nitrogen tank will be a 14 CF cylinder (just under 18” tall, fits in a kegerator), the coffee keg is 5 gallons (most everyone uses either a 5 gallon ball lock or 5.16 gallon 1/6 barrel keg), and the roaster wants to dispense the coffee at 35 pounds per square inch (35 psi on the top gauge of the regulator).

Micromatic, one of the leading beer equipment manufacturers says that a 5 pound CO2 tank will dispense 15 to 22 5-gallon kegs of beer. (http://www.micromatic.com/beer-questions/how-many-beer-kegs-dispensed-out-co2-tank)  We have observed the same thing with our own beer and with our beer customers.  A 14 CF nitrogen tank is just a 5 pound CO2 tank that has a nitrogen valve and is filled with a different gas.

One major difference is that CO2 is a combination of liquid and gas when in the cylinder and nitrogen is all gas.  This means that the pressure in a CO2 tank will not drop until all the liquid is used up.  A 20 pound sized cylinder holds 55 cubic feet of nitrogen at 1800 psi or 175 cubic feet of CO2 when filled to 20 pounds.  Put another way, the same cylinder will push a little over 3 times as much liquid with CO2 as with Nitrogen.

The other major difference is that beer is normally dispensed at 10-12 psi.  That can change with factors such as volumes of carbonation, altitude brewed, and distance from the keg to the faucet, but most direct draw kegs are fine at 12 psi.  Nitro coffee will be served at 30-45 psi, depending on the roaster’s specs.  It will take three times as much gas to push the same volume of coffee at 36 psi as at 12 psi.

CO2 is more soluble in beer than nitrogen is in coffee.  That offsets some of the difference in the volume of gas.  Between the regulator pressure and the use of nitrogen instead of CO2, cold brew coffee will only get maybe 12-20% of the “push” as beer for the same size tank.

 

Number of Kegs Dispensed per Nitrogen Cylinder

(1800 CF full dispensed at 36 psi)

 14 cubic feet (small 5#)          2-3

28 cubic feet (medium 10#)   4-6

55 cubic feet (large 20#)        8-12