KYAMBOGO UNIVERSITYFACULTY OF SCIENCE

BACHELOR OF SCIENCE IN CHEMICAL ENGINEERING

DEPARTMENT OF CHEMISTRY

CHE 315: MICRO-BIOLOGY PRESENTATION

Question6: Discuss in detail the steps in brewing of a lager beer, highlighting the micro-organisms used.

NAMES OF STUDENTS: REGISTRATION NO: SIGNATURE:

Opio Joshua Ochiba 14/U/138/CHD/GV

Kirembeka Joseph 14/U/134/CHD/GV

Gimei Benedict 14/U/132/CHD/GV

Barigye Edward 14/U/130/CHD/GV

Muyanja Derrick 14/U/6013/CHD/PD

SUBMITTED TO: MR. WACOO PAUL ALEX DATE: 11/10/2016

Brewing is the production of beer by

steeping a starch source (commonly

cereal grains, the most popular of which is

barley) in water and fermenting the

resulting sweet liquid with yeast.

BARLEY – the body & soul of beer

YEAST – the life of beer

HOPS – the spice of beer

WATER – the integrity & purity of beer

Malting is the process where barley grain is made ready

for brewing.

A. Selection of barley

B. Germination (Done by steeping)

C. Kilning

D. Milling

Maximize Enzyme

Synthesis

To Stabilize and Preserve

Enzyme Activity Well.

Malt is sprouted barley. Barley is soaked in water to begin the process of

germination, then dried and toasted for flavor.

Malting produces an enzyme, diastase, which turns starch into sugar.

• Two row barley (Mostly used)

• Six row Barley

Germination is done by steeping the

barley in cold water at 10-200C for 2 or 3

days

The Germination is accomplished by the

synthesis of myriad-enzymes.

The barley reaches its maximum enzyme

activity when the rootlets reach a length

of one-third of the size of the grain.

Barley is dried with a temperature

range of 45-600C to stop further

germination, stabilize and preserve

enzyme activity.

Milling breaks the kernels apart and

exposes the cotyledon, which contains

starches, proteins and enzymes.

Mashing is the process of combining a mixture

of milled malt with water, and heating this

mixture in a vessel called a "mash tun".

To activate the Malt Enzymes

Naturally occurring enzymes convert starch

into fermentable sugars (Saccharification)

The brewing water should have medium hardness

The pH should be between 6 and 7.

The mash (malt water mixture) is gradually heated

from 200C to 600C to 650C by infusion, decoction

or combination of the two, to extract as much sugar

as possible from the grain.

Lautering is the separation of the liquid containing

the sugar extracted during mashing from the

grains. The extracted liquid is the “wort”.

The temperature of the mash is raised to

760C which effectively inactivates all

enzyme activity.

The main component of wort other than

water is carbohydrate in form of small

fermentable sugars, the rest are carbohydrate

fractions of longer non-fermentable

oligosaccharides that include dextrins.

The final PH of the wort is around 5.2.

In the final step prior to fermentation,

the wort is moved into a large tank

known as a brew kettle where it is

boiled with hops.

Hops provide two (2) main

characteristics to beer

namely; flavour and

aroma.

Hops also enhance

preservation and increase

shelf life of beer.

1) It kills all the micro-organisms remaining after

mashing, making the wort, sterile.

2) Inactivates most of the enzymes still after the mashing

or reduces their

activity to barely detectible levels.

3) Enhances extraction of oils and resins from the hops and

accelerates isomerization of hop acids.

4) Proteins, tannins, and other materials precipitate

during the boiling step.

5) Enhances colour development by catalyzing formation

of Maillad reaction products.

6) Undesirable volatile components such as Sulphur

containing aroma compounds are removed.

7) Prolonged boiling causes evaporation of water and

concentration of the wort.

The fermentation of the wort occurs in ferment

vessels of varying, size and configuration, and

in either batch or continuous modes.

Lager fermentation vessels are typically

cylindric, with cone-shaped bottoms

(cylindroconical), so that when the yeasts

flocculate and settle, the cells collect within the

conical region.

After the wort is cooled and aerated, the yeast

culture is, at last, added to the wort, in a step

called pitching.

Lager beers are fermented by Saccharomyces

pastorianus also known as the “lager” or

“bottom-fermenting” yeast.

In contrast, when lager yeasts flocculate, the

flocks sediment to the bottom.

Larger style beers are fermented by yeast capable

of growing at temperatures below 150C.

LAGER!!

For lager beers, Conditioning or

lagering occurs in tanks held at

lower temperatures for a longer

time.

Typically, temperatures as low as

00C, for as long as three months,

can be used.

Lagering matures the beer &

mallows its flavour.

The CO2 that evolves is trapped,

and the beer becomes naturally

carbonated.

After conditioning by lagering, clarification is

done to remove any suspended yeast cells and

other micro-organisms that are still be present.

Clarification can occur via physical separation

methods such as centrifugation or by addition of

fining agents.

Fining agents act by promoting flocculation of

yeast cells and include wood chips, gelatin, and

isin glass.

Several filtration configurations exist including

plate and frame systems, leaf filters, cartridge

filters and membrane filtration.

Carbonation provides sensual appeal by

enhancing mouth feel, flavour, body and

form.

Carbondioxide preserves the beer by

reducing the PH and the redox potential

such that various aerobic, acid sensitive

spoilage organisms are inhibited.

Carbonation of beer can occur naturally via

secondary fermentation or mechanically by

directly adding carbondioxide after the

condition and clarification steps.

The simplest form of packaging is to feel the beer directly into

cans or glass bottles. The packaging steps are performed under

aseptic conditions to prevent post processing contamination.

Sterile nitrogen or carbondioxide can be used to flash the

environment and sterile water used to ensure that the relevant

equipments, especially the areas around the fillers remain free of

microbial contaminants.

After packaging, beer is heat pasteurized. Lager beer is always

processed via tunnel pasteurization systems in which filled and

sealed bottles or cans are heated by hot water.

Pasteurizing the beer after it is already in sealed packages prevents

post pasteurization contamination.

ANY QUESTIONS ??

Drink & Serve Responsibly

THE END!!!