Beer brewing begins with steeping grains in hot water, releasing the sugars insi

Question

Beer brewing begins with steeping grains in hot water, releasing the sugars inside. The sugar water is then heated to a boil and hops added. The hot temperature of the boil extracts oil from the hops and provides sanitation from unwanted bacteria. The whole mess is cooled down and once it is safe enough for yeast to survive, they are added. The yeast convert the sugar to alcohol, and the oils from the hops provide many things including flavor and antibacterial benefits. a. If 16.5 lbs of grain at 67 degree F are added to 5 gal of hot water and the equilibrium temperature of the mixture is to be 154 degree F, what must the initial temperature (strike temperature) of the hot water be? The specific heat of malt grains is about 0.44 times that of water. Also assume no energy is lost during the time the system comes to equilibrium. b. During the one hour steeping stage, where the water and grain mixture started at 2 degree the mixture only lost 2 degree What was the average energy per time lost by the mixture. c. Enhancement: For this week's enhancement l will provide you with a question. You might wonder how much did it cost to heat the 5 gallons of tap water initially at 110 degree to the strike temperature? Assume the heating takes 47 minutes, electricity costs 15 not C per kilowatt-hour, and only 10% energy is lost during heating.

Explanation / Answer

(a)

Using the heat balance equation:

Heat gained by grains = Heat lost by hot water

m1c1dT1 = m2c2dT2

Given:

c1 = 0.44*c2

Density of water, d = 8.35 lb/gal

So, mass of water taken, m2 = volume * density = 5*8.35 = 41.75 lbs

Putting values in the above eqn, we get:

16.5*0.44*c2*(154-67) = 41.75*c2*(Ti-154)

Here Ti is the initial water temp.

Solving we get:

Ti = 169.12 0F

(b)

Specific heat capacity of the mixture, cm = (m1c1 + m2c2) / (m1+m2) = (16.5*0.44*c2 + 41.75*c2)/(16.5+41.75) = 0.84*c2

For water, c2 = 1 Btu/(lb.F)

So, cm = 0.84

So, heat lost by mixture = Mass of mixture*cm*dT = (16.5+41.75)*0.84*2 = 97.86 Btu

Revert back if you have any queries.

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