|As a long time professional in the beer and brewing business I especially appreciate the fact that,, according to the
e-mails you've sent me, the readers of BeerNexus are really serious about learning more about beer and how it's
made. Because of that I thought this month's column would discuss to important parts of the brewing process.
Let's start with the lag phase. That's the period between adding yeast to wort and the beginning of fermentation.
After its arrival in the wort, yeast requires a certain amount of time to acclimate to its new environment and to shift
from dormancy to active fermentation. During the lag phase, the yeast turns on genetic pathways that allow it to
import sugar other materials needed for cell replication as well as nutrient absorption.
The lag phase may last anywhere from 3 to 15 hours, depending on such factors as wort type and gravity,
temperature, yeast strain, yeast health, pitching rate, and aeration.
During the lag phase, yeast cells rapidly absorb available oxygen. Oxygen is needed for yeast to produce
important compounds—most significantly sterols which are critical in yeast membrane permeability. Although
higher temperatures result in a shorter lag phase, brewers usually keep the lag phase temperature below the
temperature at which the yeast will eventually ferment. This is because higher temperatures during the lag phase
promote the synthesis of such substances as alpha acetolactate, which is a precursor to diacetyl.
The pitching rate, too, plays a significant role in the effectiveness and length of the lag phase. Over-pitching
can decrease the lag phase, but, because each cell grows the same number of new cells, the result may be
too many old, worn-out cells at the end of fermentation. This can lead to off- flavors and low viability if this
yeast is subsequently re-pitched.
It is also important that the lag phase not last too long, because cool, well-aerated wort is an ideal habitat
for bacteria and wild yeast. It is essential that vigorous fermentation with the desired yeast begins before any other
organisms can gain a foothold. Although most worts will remain stable for at least 24 h, it is best to err
on the side of caution and aim for active fermentation within 15 h.
Our second term is "grist" which refers to malt and cereal that is ground in the brewhouse by a malt mill at the
beginning of the brewing process. The mills can be of various designs and contain one, two, and often three pairs
of rollers, or in the case of breweries which require a very fine grist, hammer mills. Malt has traditionally been
milled in a dry state, but modern breweries often use “wet milling,” which can be more efficient. The distance
between the rollers determines how fine the grist becomes, and this determines the efficiency and speed of the
process of extracting malt sugars from the raw materials. Grist can be separated into six categories, the three main
ones being husk, grits, or flour The equipment the brewery uses to extract wort from the malt determines the
specification of the grist, with British mash/lauter tuns requiring a coarse grind, European lauter tuns a
medium grind, and mash filters a fine grind. It may sound confusing but it's really not.
Breweries monitor and control the milling process by measuring the different proportions of the grist. If a grist
has too much flour i.e. it is too finely ground, the run off process will be too slow. If a grist is too coarse the wort
separation will be fast, but the extract yield will be low and the brewing value lost.
The term “grist” is also used to refer to the “grain bill” of a beer or the cereal part of the recipe. For
Example: a brewer may refer to a beer “brewed from a grist containing 90% pale malt and 10% crystal malt.”
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!
|Lag Phase // Grist
|A new column by
|Jack O'Reilly attended the
famous Siebel Institute/ World
Brewing Academy in Chicago.
|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, #4, #5