Article reviews by David Sohigian
Republished from BrewingTechniques' July/August 1998 issue.

Hop Chemistry Made Practical

	Val Peacock, "Fundamentals of Hop Chemistry," MBAA Technical Quarterly 34 (4), pp. 4-8 (1997).

Hop chemistry is a complex topic that often has little bearing on brewing practice. This primer on hop chemistry provides practical insight, focusing on the soft resins (responsible for bitterness) and essential oils (responsible for aroma). It dispels several myths about hop chemistry that often show up in brewing literature. The first is that hop bitterness decreases with oxidation. Peacock explains how beta-acids oxidize into beer-soluble components that are quite bitter, whereas oxidized alpha-acids are less bitter than non oxidized alpha-acids. Hence, a beer made with old hops will have much more bitterness from oxidized beta-acids, which tend to give a duller, more lingering bitterness. Peacock goes on to explain how bitterness measurement is not simply a measure of isoalpha-acids, but of all of the bittering components in beer. This is important because using old hops may result in less isoalpha-acids in beer, but the perceived bitterness, and IBUs, should remain fairly constant. The article also explains the hop storage index (HSI) and describes the changes that occur in hop essential oils during aging. The final section of the article discusses hop tannins. This synopsis of the current knowledge of hop chemistry does a good job of covering the material fairly comprehensively.

Beer Flavor and Aroma

	L. Narziss, "Beer Taste and How It Is Influenced by Raw Materials and Technological Factors," Brauwelt International 15, pp. 14-25 (November 1997).

This comprehensive article covers the origins and controls of almost every beer aroma and flavor imaginable. It begins with the standard concentrations of many components for various beer styles (all German, of course). The article continues by discussing the formation of higher alcohols, esters, and sulfur compounds (including DMS). Although the article focuses on German brewing techniques, the discussion of how to alleviate problem characters applies to all brewers. Narziss also discusses beer body and how to control it. He states that water quality will affect the body of beer and that some level of hardness should be present for a full-bodied beer. He also states that high alkalinity (carbonate) will produce a full-bodied beer, but the alkalinity must be balanced by mash acidification. The article reviews the "liveliness of beer" (which seems to mean the beer's carbonation and pH), and beer bitterness, which includes bitterness derived from hop resins, tannins, proteins, and yeast. An excellent reference, this article deserves to be read from start to finish. You will find many useful and interesting techniques for the control of your beer character.

Whirlpool Tips

	V. Denk, "The Whirlpool - State of the Art l997," Brauwelt International 15, pp. 31-43 (November 1997).

This article will be of great value to anyone having problems with their whirlpool or getting ready to set up a new whirlpool. It details the operation of the whirlpool, gives a step-by-step guide on how to optimize wort clarity in the whirlpool, and presents several key concepts to help you get better results from the whirlpool. Denk points out that even when the trub pile is well shaped and compact, the total solids in the knockout wort may still be high, meaning a good trub pile should not be the only measure of good whirlpool. (The author presents a method using an Imhoff cone to determine knockout wort solids.) The article also details the optimal pump speed as it relates to the height/diameter ratio of the whirlpool (taller whirlpools accommodate slower pumps, but the height/diameter ratio should not exceed 1:1).

Another key point that is often overlooked is the rate at which wort is drawn off from the whirlpool, particularly once the trub pile becomes visible. The rate that liquid trickles out of the trub pile itself should be the same as the outflow rate from the whirlpool. In practice, this often means decreasing the knockout rate once the trub pile becomes visible. The article also details several designs for whirlpool tank bottoms, along with the design of concentric rings inside of whirlpools for reducing secondary currents that disturb trub pile formation. Denk stresses throughout the article that the conditions to which the wort is subjected before whirlpooling will affect wort clarity after whirlpooling. Overall this article gives detailed information on how to design a good whirlpool and shows why so many craft brewery whirlpools do not function to maximum efficiency.

Yeast Stressors

	S. Cunningham and G.G. Stewart, "Effects of High-Gravity Brewing and Acid Washing on Brewers' Yeast," Journal of the American Society of Brewing Chemists 56 (1), pp. 12-18 (1998).

This article discusses how the dual stresses of high gravity and acid washing affect the vitality and viability of yeast. The authors conducted experiments using various washing techniques on both low- and high-gravity worts. The tests for viability showed a small drop in viability for the acid-washed yeast in the high-gravity wort. This drop in viability lasted for only the first few hours of fermentation; the yeast seemed to recover after the initial lag phase. The study also showed a delay in the uptake of glucose in the acid-washed yeast, along with the eventual uptake of maltose, indicating an increased lag phase in the acid-washed high-gravity wort. The low-gravity fermentations did not show this same relationship, suggesting that the combination of acid washing and high gravity was the cause of the extended lag phase, rather than acid washing alone. In addition to washing the yeast with phosphoric acid, the researchers also used a phosphoric acid-ammonium persulfate wash, a method common in the UK and which is reported to give better results. As with all studies involving yeast, it is important to note that each yeast strain will react differently to acid washing, and brewers are advised to conduct their own tests to determine the effect on their yeast strain.

The Effect of High Gravity on Head Retention

	D.J. Cooper, G.G. Steward, and J.H. Bryce, "Some Reasons Why High Gravity Brewing Has a Negative Effect on Head Retention," Journal of the Institute of Brewing 104 (2), pp. 83-88 (March/April 1998).

Although this article focuses on the high-gravity brewing practices of large breweries (where a strong wort is produced and diluted before packaging the beer), some of the results are likely to be of interest to small-scale brewers. The researchers found that a beer made from a 1.040 (10 °) wort had greater foaming potential than one made from a 1.083 (20 °) wort, even on an undiluted basis. It appears that even though high-gravity worts result in higher total extraction of proteins, the fraction of those polypeptides that are key to good foam characteristics (hydrophobic polypeptides) is proportionally lower. Couple that with increased losses of hydrophobic polypeptides during fermentation (due to adherence to yeast and to the walls of the fermentor during vigorous fermentation), and the higher gravity wort actually ends up with less foam-positive proteins even before dilution. The take-home message from this article is that even microbrewers producing high-gravity beers cannot count on getting good foaming, even with high overall protein content. To preserve foam characteristics, brewers must avoid losing hydrophobic polypeptides during foaming throughout the process.