Tub Mate - Dry Ice Carbonated Yerba Mate

Yerba Mate is a caffeine containing plant used similarly to tea or coffee by many South American cultures.

In recent years, Club Mate - a sweetened and carbonated version of the beverage from Germany has become popular among hackers and others around the world.

This has inspired many people come up with their own versions of various strengths - some incorporating unique flavors.

Typically, carbonating mate or other sodas requires equipment such as kegs, a CO2 tank and regulator.

"Tub Mate" instead uses dry ice for quick and easy carbonation.

DO NOT GO AND THROW A BUNCH OF DRY ICE IN A SODA BOTTLE.  IT WILL EXPLODE - AND YOU WILL GET HURT... possibly badly.

Instructions will be provided how to do things with reduced risk.  There is still some risk involved due to the possibility of human error - or even error in these instructions.  By proceeding - you are assuming all risk.  Kids - don't try this.

You can be drinking your own carbonated mate in under 45 minutes!

This technique should also work to carbonate other beverages such as soda or beer.

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If you like projects involving radioactivity, lasers or robots you should check outhttp://nothinglabs.com

Step 1: Safety First

This project calls for adding a very small amount of dry ice to a closed container.    This is only safe-ish because we are adding such a tiny (and well measured) amount.

Adding too much dry ice - or using the wrong container may result in an explosion.  In the worst case - this could seriously injure or possibly even kill you.

---MANDATORY READING---
HOW TO AVOID BLOWING YOURSELF UP:

Never use a container other than a 2-liter plastic soda pop bottle
-Do not use a glass container!!!!  You really might kill yourself.
-Do not use a smaller 16 or 20oz plastic pop container - these are not as robust - and may explode (trust me)
-Do not use a bottle that seems damaged / stretched from pressure

NEVER place the 2-liter soda pop bottle in the freezer
- This may cause it to shatter / blow up in your face (trust me)

Pay close attention to the measurements of dry ice
- The provided measurements will be in teaspoons / grams
- Do not confuse this with tablespoons / ounces
- Do not add more dry ice than is specified

Watch this video of too much dry ice in a 2-liter bottle blowing up a cinder block:

Step 2: Stuff You'll Need

A Bag of Loose Yerba Mate
Any brand is fine
Check your local Latin American grocery store  -  they commonly have mate about 75% cheaper than other places
Also available at many grocery / health food stores or where loose tea is sold

Dry Ice
Often available from the meat department of your grocery store
Do not handle directly - use gloves!  It can burn you quickly!
We'll only be using about 6-8 grams per bottle - but since it evaporates - get at least a pound or two

2-Liter Plastic Pop Bottle
No substitutions allowed!
Bottle should be undamaged / in general good condition
If you want to end up with individual servings - carbonate in the 2-litter bottle - then transfer to other containers

1/2 Teaspoon Measuring Spoon
You'll need other measuring cups / spoons - but this one is important!

Hammer
To crush dry ice (may want to wash it if it's been sitting in your toolbox)

Sturdy Metal or Plastic Bowl
To crush the dry ice in - I use a small plastic measuring cup
If it's plastic - be prepared that it might break.
Do not use glass / ceramic!

French Press
If you don't have one - you can probably figure out an alternative

Sugar

Lemon Juice
Lime juice also works

Step 3: Carbonation / Dry Ice Theory

Dry ice is frozen CO2.

Beverages are carbonated by dissolving CO2 into them under pressure. 

One source suggests a 2-liter bottle of Pepsi contains roughly 10 grams CO2.

To allow a little extra safety - we're going to target 6-8 grams per bottle.  This also seems to be a nice, light carbonation level for mate.

However - the 2-liter bottle isn't designed to handle the pressure required to carbonate - only to store carbonation.

If you added 8 grams of dry ice at once to the bottle - much of the resulting CO2 gas would not immediately dissolve into the liquid.  This would create more pressure than the same amount of CO2 would if it was already dissolved into the liquid.

This level of pressure could cause an explosion!

Instead - we will be adding a small amount (2 grams) of CO2 (dry ice) in several small doses.  Each time assuring the CO2 has fully dissolved into the liquid before adding more. 

You won't need a precision scale to measure the dry ice.  We'll be crushing it to a snow-like powder which reliably weighs about 2 grams per 1/2 level teaspoon.

Let's stop and note that measurement now.  That's 1/2 level teaspoon.  Do not confuse this with tablespoon.  Do not use a "rounded" teaspoon.

The powder also provides a large surface area - and dissolves into the liquid quickly.

CO2 dissolves more readily into cold liquids.  We don't need our mate ice-cold - but it needs to be at least cooler than room temperature to get good carbonation results.

Image credit: Arie Melamed-Katz

Step 4: Caffeine Theory

This page includes several references as to the caffeine content of yerba mate:

http://www.erowid.org/plants/yerba_mate/yerba_mate_chemistry2.shtml

In short - using hot water to extract caffeine from mate typically yields 0.5% to 2.0% caffeine by weight.  However - most test results came in right around 1%.  We'll use that number to guesstimate.

So - we're making 2-liters (67.6oz) of mate in this recipe.

Let's call that 4 generous 16.9oz servings.

My own measurements put 1 cup mate (volume) at 72 grams (weight).

Let's say we put 1/2 cup (36 grams) of mate into our 2-liter batch:

36 grams * 1% = 360 milligrams total caffeine

360 milligrams / 4 servings = 90 milligrams per 16.9oz serving.

For reference Club Mate comes in at 100mg caffeine for the same size serving!  That's certainly within our margin of error.

However - to get this level of caffeine - Club Mate adds extracted caffeine to their recipe.  So - using this amount of mate in our recipe yields a little "richer" flavor.

Mate varies in strength and density -  be aware that it's possible these guesstimates are off by a factor of 2x in either direction.  If you are caffeine sensitive - avoid mate.

For further reference - drip coffee comes in around 145mg caffeine for an 8oz serving.

Step 5: Recipe Options

Here are a few recipes to try - each one makes 2-liters mate (additional instructions in next steps)

The amount of sugar and citrus are based on a combination of research and my own taste.

Mate Light
Similar in flavor to Club Mate - little less caffeine (60mg per serving)
1/3 cup mate
1/3 cup sugar
1 teaspoon lemon juice

Mate Extra
A bit richer tasting than Club Mate - with similar caffeine (90mg per serving)
1/2 cup mate
1/3 cup + 1 tablespoon sugar
1 1/4 teaspoon lemon juice

Imperial Mate
More Flavor! More Caffeine! (135mg per serviing!)
3/4 cup mate
1/2 cup sugar
1 1/2 teaspoon lemon juice

Insert Your Recipe Here
Tweak the variables a little - or do your own thing.
Add ginger, raspberry, chile powder!

Note: Large amounts of strong mate can make your tummy unhappy.  You've been warned.

Step 6: Fill Pop Bottle Half Full With Water

Fill the 2-liter pop bottle half full of cold water (about 4 cups).

Run the faucet a while to get the water as cold as possible.

When done - put the bottle in your refrigerator to further chill.

DO NOT PUT THE BOTTLE IN THE FREEZER
This will cause it to become brittle - and may shatter / explode when carbonating.

Note - I don't actually recommend taking the bottle's label off as shown in the photo.  It leaves a sticky residue.

Step 7: Add Ingredients to French Press

Pick which recipe you want to use from the prior step - then put all the ingredients into your French Press.

Step 8: Add Hot Water - Then Stir

Add roughly 3 1/2 cups not-quite-boiling water to the French Press.

If you boil water - then let it sit a few minutes afterwards - you'll get the temperature about right.

Don't worry about the exact temperature or amount of water (just not more than 4 cups - or you might run out of room in the bottle later).

Use a spoon to stir everything (make sure the sugar isn't sticking to the bottom).

Note: I have a giant French Press (thanks Beth!) - yours will probably look more full with the same amount of liquid.

Step 9: Let Stand 5-15 Minutes - Then Press

Plunge the French Press after 5-15 minutes of steeping.

Caffeine extracts pretty easily - you'll probably get most of it within a few minutes.

I commonly plunge the French Press after about 7 minutes.

But - going a bit longer may get you a tad more caffeine - and more mate flavor.

It's up to you!

Step 10: Cool French Press in Sink

In order to effectively carbonate - you'll need to get the temperature of the mate in the French Press down to around room temperature.

To speed this process up - fill your sink with cold water - then let your French Press sit in it.

You should find it close to room temperature within about 15 minutes.

When it's no longer warm to the touch - you're ready for the next step.

Step 11: Pour French Press Contents Into Bottle

Pour the contents of the French Press into the 2-liter pop bottle.

Step 12: Top Off Bottle With Cold Water

Fill any remaining space in the 2-liter bottle with cold water.  Leave as little air in the top of bottle as possible.

You may optionally further chill the mate in your refrigerator (not freezer!) at this point.  Doing so may provide a bit better carbonation results.  The colder the liquid - the more easily the CO2 will dissolve into it.

Step 13: Crush Dry Ice

Place a few small chunks of dry ice into your crushing container.

Use gloves - the dry ice can burn you!

Lightly crush the dry ice using the hammer (you don't need to use a lot of force).

Continue crushing until the powder resembles course snow.

Step 14: Add 1/2 Level Teaspoon Dry Ice to Bottle and Shake! (then Repeat)

Do this step over the sink!  If you don't get the cap back on quickly enough - the mate may overflow.  It may also overflow when opening the bottle.  The colder the mate - the less likely things will overflow on you.

Do not add all the dry ice at once!  It will explode.

We are going to be adding 1/2 level teaspoon (2 grams) of dry ice at a time.

One last time - that's 1/2 level teaspoon -  not tablespoon.  Tablespoons are bigger - and may in this case cause an explosion.

And again - 1/2 level teaspoon.  Not a rounded 1/2 teaspoon.

Perform the following steps quickly:

1. Measure 1/2 level teaspoon of the dry ice powder
2. Dump the 1/2 level teaspoon of dry ice into the 2-liter bottle
3. Immediately place the cap back on the bottle
4. Immediately shake the bottle vigorously!
5. Place thumb on bottle - note slight pressure building in bottle (keep shaking!)
6. Once the pressure has peaked, then subsided - you may stop shaking
7. Slowly remove cap from bottle (don't be alarmed if it fizzes over a bit)

When done - repeat this process twice more.  Powder more dry ice if needed.

If you want more carbonation - you can repeat one additional time.

Step 15: Chill, Serve and Hack! (plus Mate Resources)

At this point the mate is probably a bit cooler than room temperature - drinkable - although would probably benefit from some time in the fridge.

Enjoy your "Tub Mate" - but once you're comfortable with the process (or before) - hack up your own modified version!

I (and others) have found lime and ginger make great additions to the recipe.  You probably have your own ideas. 

There's lots of people making mate - check out their recipes and get inspired!
https://www.noisebridge.net/wiki/Sudo_pop
https://github.com/jdukes/ShadowMate
http://www.hackpittsburgh.org/brewing-open-mate-soda
https://gist.github.com/1054447

Blatant Self Promotion
If you like projects involving radioactivity, lasers or robots you should check outhttp://nothinglabs.com