Article reviews by David Sohigian
Republished from BrewingTechniques' May/June 1998 issue.

Determining Yeast Viability

	Dr. Erin O'Connor-Cox, "Improving Yeast Handling in the Brewery, Part 1: Yeast Cropping," Brewers' Guardian, pp. 26-34 (December 1997).

Written from the viewpoint of a major brewery (located in South Africa), this well-composed article manages to convey key points of interest to all brewers. Part one of three parts discusses various methods of measuring yeast viability, noting the weaknesses of methylene blue staining, and proposes measuring yeast slurry pH to help determine yeast viability. If the pH of the yeast slurry is >0.5 pH units higher than that of the beer, the yeast has probably undergone considerable autolysis and is of poor viability. Dealing with non- flocculent yeast is also discussed, but most of the options for cropping (for example, centrifugation) are well outside small brewers' budgets. The article also mentions the importance of measuring the quantity of the crop when harvesting; crop size provides an indication of the fermentation performance (poor yeast growth can indicate problems with yeast health).

Yeast Storage Tips

	Dr. Erin O'Connor-Cox, "Improving Yeast Handling in the Brewery, Part 2: Yeast Collection," Brewers Guardian, pp. 22-34 (February 1998).

The second article in this three-part series has some extremely practical tips for yeast storage, although much of it will be of use only to larger micros and regional breweries. Using case studies drawn from her own brewery, Dr. O'Connor-Cox demonstrates that the key to avoiding yeast degeneration is to keep the slurry cool and oxygen-free during both harvesting and storage. She also proposes that CO2 is detrimental to yeast not only during the growth phase (as is commonly accepted) but also during the stationary phase. She supports this theory by showing that yeast exposed to CO2 in nongrowth conditions show an increased level of trehalose, which indicates that the yeast is stressed.

Methods of deaerating the yeast slurry are included, along with the acid wash method of decontamination. O'Connor-Cox also points out that a much milder form of acid washing, called acid conditioning, is used at her brewery to deflocculate the yeast before pitching to shorten the lag phase. She also makes the somewhat controversial point that yeast should not be aerated before pitching, arguing that it will result in yeast degradation (she suggests aerating the wort instead, a practice that many small-scale brewers use by necessity). The many other insights contained in this article make it a valuable resource for any brewery storing their yeast outside of the cone of the fermentor.

Optimizing Yeast Pitching

	Dr. Erin O'Connor-Cox, "Improving Yeast Handling in the Brewery, Part 3: Yeast Pitching and Measurement of Yeast Quality," Brewers Guardian, pp. 20-26 (March 1998).

In the final installment on yeast handling, Dr. O'Connor-Cox covers the optimum conditions for pitching yeast and summarizes the various methods of analyzing yeast quality. O'Connor-Cox stresses the importance of a consistent pitch rate for good cell health and refers often to how the advent of high-gravity brewing led to poor yeast performance before corrections were made to the pitching rate. This material applies well to small-scale brewers, because much of our brewing would be considered "high gravity." The author notes that adjusting the pitching rate too high can have negative results because the poor yeast growth will lead to older and older cell populations in subsequent fermentations. She also mentions that cone-to-cone pitching can be an advantageous procedure as long as the yeast is not left under the beer for too long.

The Effect of Water Quality on Cleaning Chemicals

	A. Ahrens and G. Schumann, "Water Treatment, Cleaning and Disinfection Specifications," Brauwelt International 15 (4/97), pp. 408-412 (November 1997).

The quality of the water used to dilute chemicals for cleaning and disinfecting will affect the efficiency and usage rate of those chemicals. This article examines the types of water suitable for use with many of the chemicals used inU.S. microbreweries. In general, drinking water quality is required (particularly for disinfectants), and soft water is preferred for many cleaning agents. Iron seems to have a particularly negative effect on many disinfecting agents (including chlorine dioxide, chlorine, and peracetic acid). One of the most interesting conclusions of the article is that brewers should use soft water for the initial dilution of quaternary ammoniums and hard water for more efficient rinsing.

Efficient Brewhouse Configuration

	John Mallet, "Brewery Configuration for Craft Brewing Optimization," MBAA Technical Quarterly 34 (4), pp. 252-256 (1997).

This article takes a practical look at designing and improving microbrewery operations. Mallet focuses on brewhouse capacity and efficiency and looks at alternative configurations to increase brewhouse throughput. He discusses hot-side aeration, and although the effects of hot-side aeration are a matter of opinion Mallet offers some inexpensive and effective methods for controlling oxidation that are certainly worth considering (for example, Mallet recommends eliminating an open grant and replacing it with a variable speed pump and check valve for lauter run-off). Wort cooling and liquor requirements are well addressed and the article concludes with some valuable safety tips centered on brewpub operations.

Fining Performance

	R.V. Leather, "From Field to Firkin: An Integrated Approach to Beer Clarification and Quality," Journal of the Institute of Brewing 104 (1), pp. 9-18 (January/February 1998).

This excellent article covers all the factors in brewing destined to affect beer clarification, with a focus on isinglass finings. It discusses the role of kettle finings, auxiliary finings, and process variables in isinglass fining performance. The strength of the article is that it discusses the relationship between initial raw materials and processing before fining and their final effect on the fining's performance. It also discusses contaminant levels in fining agents (they are found to be significantly lower than the levels found in beer) and the relative effect finings have on filtration performance and foam stability (many beers fined with isinglass demonstrate improved foam stability). If you are currently using isinglass or copper finings in your brewery, or plan to in the future, this article is an excellent reference that covers most of what you need to know.