It's a beer world after all!
Most people don't know that Louis Pasteur is credited as the first person to understand the process
of fermentation and the importance of microorganisms in the production and spoilage of beer.  
Yes, that's beer, not milk!

His observations on the heat treatment of beer to prevent microbial spoilage became known a

s “pasteurization.” Before Pasteur’s definitive statements on the nature of fermentation, it had been
thought that the products of fermentation arose from “spontaneous generation,” which, in essence,
propounded that “life” was continually being created out of inanimate matter.

In 1860 Pasteur wrote, “Alcoholic fermentation is an act correlated with the life and organization of yeast cells,

not with the death and putrefaction of the cells, any more than it is a phenomenon of contact, in which case
the transformation of sugar would be accomplished in the presence of the ferment without yielding up to it or
taking from anything.” By 1875 Pasteur had concluded that fermentation was the result of life without oxygen,
whereby, in the absence of free oxygen in the atmosphere, cells were able to obtain energy which was

liberated by the decomposition of substances containing combined oxygen.

In 1876 h
e published his groundbreaking book Etudes sur la Biere in which he dealt with the diseases
of beer and described how the fermenting yeast was often contaminated by bacteria, filamentous fungi,
and other yeasts.

In Pasteur’s own words, “Every unhealthy change in the quality of beer coincides with the development of
microscopic germs which are alien to the pure ferment of the beer” (1877). These unwelcome organisms had
come into contact with the beer as a result of contamination in the production environment or through
contaminated yeast. Pasteur observed that by holding beer at between 131°F and 149°F (55°C–60°C) for

a short time the growth of beer spoilage organisms was inhibited and the beer could be rendered palatable
for up to 9 months. This is the basis of the process of pasteurization.

Pasteur, it is said, was not a great lover of beer, but as a result of the Franco-Prussian War of 1870, the out
come of which resulted in France ceding the hop-growing region of Alsace-Lorraine, Pasteur had an animosity
for all things German. This resulted in his determination to improve the quality of French-made beers, or as
Pasteur himself stated, to make the “Beer of National Revenge”!


I received several e-mails asking me to discuss oatmeal stout.  Technically oatmeal stout is a sub-style
of stout, being differentiated by the inclusion of up to 20% oats by weight in the grist. he addition of oats,
a cereal grain with high concentrations adds a distinctly silky and rich mouth feel to the beer.

Stouts brewed with oatmeal became popular in late 19th-century England, with the stout style in
general, and oatmeal stouts in particular, being associated with nourishment and viewed as healthful,
restorative drinks. By the middle of the 20th century, however, the style had largely disappeared.

A mention of oatmeal stout in Michael Jackson’s 1977 The World Guide to Beer led an American beer
importer to commission such a beer from Samuel Smith, a brewery in Yorkshire, England. Since the creation
of thatfirst modern oatmeal stout, the style has grown in popularity with more than 100 commercially
brewed examples available today.

Oats are most often used as rolled oats, added directly to the mash, usually at around 10%–15% of total grist
weight. Alcohol content by volume varies from as little as 4% to as high as 7.5%, with most examples below 6%.
Oatmeal stouts are often somewhat sweeter than dry stouts, but less sweet than sweet stouts or milk stouts. Hop
bitterness varies with each brewer’s interpretation of the style but is generally moderate, with an emphasis on
bittering, rather than aroma hops.


Hope you found this month's column of interest.  If you have any questions about beer or brewing

or just want to submit a word for me to discuss here just e-mail it to me.

Thanks and Cheers!
Louis Pasteur and Beer //  Oatmeal Stout
A new column by
Jack O'Reilly
Jack O'Reilly attended the
Siebel Institute/ World
Brewing Academy
I'm very excited to be part of the BeerNexus team.  I think my many years in the
beer business both as a brewer and manger will enable me to explain and
investigate many topics of interest for those who really love craft beer. Hope you
join me every month.  
More by Jack: #1, #2, #3