Hopped wort agar preparation and yeast viability count are some of the most important microbiological analyses and tests carried out in the laboratory of a brewing industry especially for lager beer. Microorganisms such as bacteria, fungi and even protozoa can all be implicated in a food contamination scandal in a brew house. It is to this end that the quality control department must carry out all necessary microbial analysis in order to certify the sterility and wholesomeness of all the brewed products.
Hopped wort agar is a microbiological media that is used in growing bacteria from hopped wort(i.e. wort that has hops added to it). The preparation of hopped wort agar must be done following strict microbiological procedure to ensure accuracy and precision of results. The preparation of hopped wort agar is as follows:
A measured volume of filtered wort is atemperated at 20ºC and the specific gravity taken with the aid of a density bottle. The standard present gravity of wort in the wort kettle is 11.9ºp
RV(Required volume) represents 1000ml while RG(Required gravity) is 6.5 which is the requires standard. V2 represents the volume of water to be added to the wort in order to make it up to 1000ml. The wort is then made up to 1000ml with the appropriately calculated volume of water, and dispensed into flasks where 7g of bacteriological media is added and then autoclaved.
In order to achieve the stepping down, we apply this formular
RG = OG x V2
Where, RG = Required gravity
RV = Required volume
OG = Original volume
V2 = ?
V2 = RG x RV/OG = 6.5x 1000/11.9 = 546m/s
Therefore, 1000 – 546 = 454ml of water to be added.
Yeast Viability Count
1ml of a wort sample is taken from the propagation tank or fermentation vessel, 1ml acetic acid, 1ml blue indicator and 7ml ringer solution are all added and mixed together. A little drop of the dilution is taken and mounted on the microscope, where the number of dead and living cells is counted. It is observed that the live cells adopt the color of the indicator while the dead cells appear black.
A-B/C x 100 = Yeast viability count
Where, A = total number of live cells
B = total number of dead cells
C = Overall number of dead + live cells