Cold Brewing in Bulk

[Jeebas]

Warning, this thread is likely gonna be a data dump, but hopefully it will help people looking to get started brewing cold brew in bulk at home.

After starting out with a Hario Cold Brew Pot I got tired of brewing coffee every night so wanted to find a way to make coffee in bulk.

So for the past 2.5 years I have been making cold brew in my old 5G brewpot with a grain bag. More recently I switched to this Mini Stainless Steel Cold Brew Coffee Maker from Keg Outlet / Cold Brew Ave. First off I will go over my old process -

Initially I did 1lb of coffee to 6 quarts of water, which ended up making about 1.25 gallons (5 quarts) of RTD (ready to drink) cold brew (this ratio of oz of coffee / cups of water of 0.6667 falls in line with what others had suggested for RTD cold brew.

After starting out trying some blends from Commonplace Coffee (a local Pittsburgh roastery) that they had at work in my Hario. I have used (and still use to this day) Kirkland Signature™ Colombian Supremo Whole Bean because it's very decent and like $15 for 3 lbs. so like .31 per oz instead of the 1.18 per oz I would pay for "artisan coffee" (not knocking it, it's awesome coffee, but for making bulk finding a happy medium between taste and price is key)

Yeah that's a grainbag and a... binder clip to hold it closed. Yummm plastic. I would suggest maybe using something else more sanitary, but I did this for over two years and have no extra limbs that I know of.

Dunk the bag in the water and maker sure it is fully submerged.

In the fridge it goes I normally did 24 hours with this method but sometimes less and sometimes 36 hours if I didn't have time to bottle it when it was "done".

Here you can see the bowls that I used to ensure that bag stayed submerged during the brew.

I would then strain the bag and squeeze it. I am not sure if this imparts bitterness or not but I didn't have time to wait for the water to drain from gravity.

I would then pour from the brewpot into these growlers through the filtered funnel which caught anything that had escaped the bag.

As far as cleaning I would wash the pot, lid, funnel and clip as I would wash any other dish (sponge and dishsoap). Then I would dump the grounds and spray out any stray ground from the bag, turn it inside out and repeat. Every month or so I would run the bag through the top level of the dishwasher then spray it out. I would replace the grain bag once every few months. I definitely could have been better about cleaning and replacing the bags but this worked for me just fine.

At some point my coffee consumption increased - I drink about 24-30 oz of RTD cold brew a day now (it's worth mentioning that I don't drink normal hot brewed coffee or any other source of caffeine) - so I started doing 1.5 lbs at a time with 9 quarts of water. The ratio was the same as above 0.667, I'll get into ratios in my next post.

 

[Jeebas]

So let's talk ratios here for a minute...

For most of my cold brewing life (last 2.5 years) I have been using what I'll call BIAB (Brew in a Bag) as I laid out in the post above. My wife would pick up the coffee from CostCo and grind it at a 4 on the scale of 1-13 on the Costco grinder where lower is finer. We did this for so long because I hadn't done my research and didn't think it mattered.

Let's throw a few terms out there:
"coffee / water ratio" - this is not so much a ratio as X to X, more like X oz of coffee / X cups of water. Why ounces and cups - oz is the lowest sane measurement of how coffee is packaged where I live. Cups I used because its the lower measurement (I would much rather use quarts or even gallons but smaller the better) without messing around with ounces of liquid. all that out of the way, the higher the "C/W Ratio" the stronger the coffee is going to be.
"absorption rate" - simply put, how many cups of water each ounce of coffee soaks up. In this next example, the number is .125 because we used 36 cups of water and got 33 cups of coffee, thus loosing 3 cup in the process. 3/24 = .125

In my BIAB batches:
Coffee (oz): 24
Waters (cups): 36
Yield (cups): 33
C/W Ratio: 0.667
Absorption Rate: 0.125

Keg Outlet / Cold Brew Ave have a neat PDF that you can get here - https://www.kegoutlet.com/the-ultimate-guide-to-cold-brewed-coffee-and-serving-coffee-on-draft.html

It suggests the following ratios:

RTD (Ready-to-Drink)
Coffee (oz): 16
Waters (cups): 24
Yield (cups): 23
C/W Ratio: 0.667
Absorption Rate: 0.0625

Concentrate
Coffee (oz): 16
Waters (cups): 10
Yield (cups): 9
C/W Ratio: 1.6
Absorption Rate: 0.0625

As you can see the RTD numbers match mine in terms of ratio and that makes sense, as I had been making RTD cold brew. The absorption is a bit different but I am willing to bet that has to do with the grind of the coffee.

As a minor point, I find it curious that the numbers mentioned on KO's page for the Mini Stainless Steel Cold Brew Coffee Maker do not match what they suggest in their PDF (their RTD is closer to a 0.5 C/W ratio and their concentrate is around a 1.0 C/W ratio) but I will chalk that up to catering numbers to the product whereas the PDF is geared towards general cold brewing, not focused on a product. That all being, KO / CBA has a wealth of free good info out there about cold brewing, and I am very much appreciative of it.

 

[Jeebas]

So I don't have any pics from my first batch but I do have some notes:

Batch #: 1
Brand: Kirkland Signature™ Colombian Supremo
Brew Time: 5/3/2016 19:00:00 - 5/4/2016 7:00:00 (12 hours)
Coffee (oz): 48
Water (cups): 44
Yield (cups): 33
C/W Ratio: 1.090909091
Absorption Rate: 0.2291666667

Notes:
This was my first use of the Mini Stainless Steel Cold Brew Coffee Maker. Lessons learned:
#1 I filled the kettle with water first and then lowered the basket of grounds into it and the grounds almost flowed out of the basket into the kettle. Maybe measure the water separately (use old brew pot) and pour over the grounds.
#2 I initially did 3 lbs (48 oz) and 9 quarts (36 cups) but some of the coffee in the basket sat higher than the water, so I added 2 more quarts bringing it to 11 quarts (44 cups).
#3 When bottling, I held the basket over the kettle which was mechanically awkward and was going to take too long to let it drip out due to fineness of the mesh. Maybe next time I leave the basket in, get what I can and then let it sit for another 30 minutes, take the basket out and dump what I can, since the dip tube won't get every last bit. I use the funnel filter anyways to transfer to the growlers.
#4 I was rushed when doing the initial cleaning of the system and need to install the ball valve better, the external O-ring was pinched in one spot and let some drops through.
#5 Buy some silicone tubing for the ball valve.
#6 The difference in yield - My past BIAB batches I would use 9-9.5 quarts (I never measured precisely) of water with 1.5 lbs of coffee and would get around 8 quarts of yield. So 1.5 lbs of coffee would absorb 1-1.5 quarts of water. I guess it only makes sense that on this batch, the 3 lbs of coffee absorbed 11 cups (almost 3 quarts).
#7 I was initially aiming for a ratio of 7.5 quarts (30 cups) for 3 lbs, but at some point, due to the dimensions of the water, you need X water to cover Y coffee and even 9 quarts didn't do the job. I think at smaller numbers this will be more attainable.
#8 First mix ratio 1:1. This is the bare minimum to make this 3 lb batch last as long as two 1.5 lb batches like I had been doing. I am trying this is the morning since I need stronger coffee then. This tastes about right, if not smoother than my past BIAB batches, but I'm not sure if this is because of the 12 vs 24 hour or concentrate vs RTD or even the strength /yield difference from the grain bag vs the steel mesh basket. My coworker says it looks lighter than my normal stuff.
#9 Second mix ratio 1:2. This isn't bad but certainly tastes lighter than the other. Not bad overall though.
#10 After a day or two, I found a pretty good ratio for this batch of 2:3, so 6 oz of concentrate and 9 oz of water for a 15oz very full pint glass. This worked out easier (and cleaner) for me when I poured 13 oz of water into my 33 oz thermos and topped the rest off with water.