Doing some math…for Beer

A new and hopefully on going project I am pursuing is producing “micro-batches” of beer. I am defining a micro-batch as any brew that is in the one to two gallon range. This is a way I can test out recipes. To see if a certain combination of grains tastes as good as I think or if the combination of hops is good for IPA use. This is to check out these ideas before scaling them up to full 5-gallon (and beyond) batches.

Amongst the first things to figure out is the amount of ingredients needed. Calculations are needed to figure out how much grains and malt are needed to include in such small batch amounts. There are recipes calculators on the web, but most of these are calibrated for 5 gallon or greater amounts. For good reason. This is temperature sensitive stuff I am dealing with here. Get it too hot and I can ruin it. If I fail to get it to hot enough I run the chance of having the batch spoiled by bacterial invaders.

The reason larger batches is easier to work with is because of physics. Water takes a lot of energy to heat up. 4.1855 J/(g·K) to be precise. That’s Joules per gram-degree Kelvin. What that says is that for every cubic centimeter of water you want to raise 1 degree Kelvin (or Celsius), 4.1855 Joules of energy need to be added to that cubic centimeter.

Let’s scale that up and apply it to the situation here. 1 litre of water is 1000 cubic centimeters. To get the entire litre of water to come up 1 degree C you need to give it 4.1855 x 1000 Joules of energy, or 4185.5 Joules. If you start off at around room temperature, say 25 deg C, and want to get to to 100 deg C, the boiling point of water, multiply that by 75 for a total of 313912.5 Joules. To do an amount of water for a normal hobby batch of beer, you’d have about 19 liters of water for a grand total of 5964337.5 Joules.

It helps to know how much heat your cook-top puts out. Thankfully, most cook-tops are rated in Watts and a Watt is Joules per second meaning we don’t have to worry about unit conversions. For instance if your cook-top outputs 100 Watts at its max setting, you’ll need 59643 seconds to get that water up to boiling. Which is just over sixteen and a half hours. Obviously most cook-tops have a better output than that, so check your owner’s manual to see what yours is rated at.

Back to the beer.

How much of the ingredients do I need?

It depends on what I choose to use. In this case I am going with DME or dry malt extract. Being able to get it in small quantities helps but if I could not get the small quantity, I know that it has an excellent shelf life and only needs a dry cool area to be stored in, making easier to store than it’s close brother, liquid malt extract.

If I were going with a normal five gallon batch, I could use a few calculations to figure out how much I need to get. To figure that out, I need to know how many points that DME gives when dissolved in water. You can go here to see where I got some of the information. The DME I got from the store, Bacchus and Barleycorn, is rated at 42 points. That also gives me some idea how much alcohol is going to be in the final. Of course I should be getting a hydrometer one of these days so I can tell exactly how potent my beers are.

Hops is the final consideration. How much?

Considering that I normally hop with 2 to 4 ounces, a quick calculation shows that I only need a few buds. However, I bought a full ounce of Mount Hood pellets. They have an AA of 3.9 which is low but given that the whole amount is going into only a gallon of beer, they’re still going to be fairly potent. Hopefully those who try this with me like IPA as much as I do. Current play is to boil half and then dry hop the other half at the end. It should be very good.

I’ll make an update after I get this going and will have some pictures documenting the process.

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