Table of Contents

Contents:

      • What is beering? and why this blog?
        A very brief introduction to this blog.


      • numbers
        A variety of measurements and how they were obtained.  Hopefully useful as an obscure reference when you want to know, for example, the weight of one cup of dried malt extract or one teaspoon of calcium chloride.


      • Hop Stand Experiment #1
        A taste test of five beers brewed with hops added in a hop stand at different (below-boiling) temperatures.


      • Hops Harvest
        Some stats (drying time, weight, alpha acid percent) and notes on my Cascade and Willamette hops over the years.


      • Hop Stand Experiment #2
        A taste test of five beers to determine why the results from Hop Stand Experiment #1 had fuller body but not a lot of hops flavor.


      • A Modified IBU Calculation (Especially for Late Hopping and Whirlpool Hops)
        A way to modify the Tinseth formula for IBU calculations in order to take into account utilization (and hence bitterness) after flameout.


      • Late Hop Experiment #1 (a.k.a. Hop-Stand Experiment #3)
        A taste test of five beers to evaluate different techniques for increasing hops flavor.


      • Dry Hopping in a Weighted Mesh Bag
        An explanation of the technique I use to maximize contact between hops and beer when dry hopping.


      • Techniques for Maximizing Hop Flavor and Aroma
        A summary of hop flavor and aroma techniques resulting from these experiments and my general experience.


      • An Analysis of Sub-Boiling Hop Utilization
        An experiment that looks at measured IBU values as a function of temperature.  These results are discussed in the context of theoretical utilization as a function of temperature.


      • A Summary of Factors Affecting IBUs
        A long-winded analysis of what affects IBU values, and a quantitative model built from the literature and various experiments.


      • mIBU Experiments #1 and #3
        An evaluation of the mIBU technique described in a previous blog post.


      • Four Experiments on Alpha-Acid Utilization and IBUs
        A series of experiments that look at (a) the difference between loose hops and hops in  a mesh bag, (b) the impact of age on IBUs, (c) the impact of malt polyphenols on IBUs, and (d) a hopping-rate correction factor based on estimated alpha-acid solubility at boiling.


      • Hopping Rate Correction Based on Alpha-Acid Solubility
        This post develops a refinement of the hopping-rate correction factor introduced in the previous post.  The new model has the solubility limit change gradually as a function of initial alpha-acid concentration.  The experimental data looks at how utilization at high hopping rates changes during the boil; the good news is that the model doesn’t seem to need any such time dependency.


      • An On-Line Calculator for the mIBU Technique
        A link to an on-line calculator for predicting IBUs using the mIBU method, and some documentation for this calculator.


      • Predicting Wort Temperature After Flameout
        This post develops a model for predicting the temperature of wort as it cools naturally after flameout.  The intended purpose is for use in the mIBU method.


      • Estimating Isomerized Alpha Acids and nonIAA from Multiple IBU Measurements
        This post describes a technique for estimating concentrations of isomerized alpha acid (IAA) and “auxiliary bittering compound” (ABC, also called nonIAA) from multiple IBU measurements.


      • Some Observations of Mash and Wort pH
        This post looks at mash and wort pH characteristics of two-row malt and DME.  While there’s nothing really new here, the plots of measured pH values might be interesting to some homebrewers.


      • The Effect of pH on Utilization and IBUs
        This post evaluates how the wort pH affects IBUs.  Based on an estimation of the concentrations of isomerized alpha acids and “auxiliary bitter compounds” (ABC), it seems that the reduction of IBUs with a decrease in pH is caused primarily by losses of ABC.  This post proposes a modification to the Tinseth formula to account for the effects of wort pH.


      • Alpha-Acid Solubility and pH
        This post looks at how wort pH affects alpha-acid solubility.  Despite expectations that a lower pH would decrease solubility at boiling, the data don’t show any effect of pH on alpha-acid solubility.


      • The Effect of Calcium Chloride on IBUs
        This post looks at the effect of calcium chloride on IBUs.  It finds little, if any, impact.


      • The Impact of Krausen Loss on IBUs
        This post looks at how the removal of krausen impacts IBUs.  The use of a blow-off tube to remove most of the krausen can result in a 25% loss of IBUs, compared with mixing the krausen back into the fermenting beer.


      • The Relative Contribution of Oxidized Alpha- and Beta-Acids to the IBU
        This post looks at how much of the IBU is composed of oxidized alpha acids and oxidized beta acids.  It finds that in a “typical” beer using well-preserved hops, oxidized alpha acids are by far the greatest component of the auxiliary bittering compounds, followed by malt polyphenols, then hop polyphenols, and finally oxidized beta acids.  At a steep time of 10 minutes, the contribution of oxidized alpha acids can equal the contribution of isomerized alpha acids.


      • Specific Gravity and IBUs
        This post looks at how IBUs are affected by the specific gravity of wort.  It finds an unexpected lack of impact at boil times less than 40 minutes.  The data from a 40-minute boil time fit well with previous models of this effect, especially the Mosher model.


      • The Production of Oxidized Alpha Acids at Hop-Stand Temperatures
        This post estimates how much impact temperature has on the production of oxidized alpha acids. It finds little impact at typical hop-stand temperatures. This post also compares beer polyphenol concentrations predicted from a model with measured polyphenol concentrations, and finds good agreement between the two.


      • How Lautering and Wort Clarity Affect IBUs
        This post estimates how different lautering techniques and the resulting wort clarity affects IBUs.  It finds that there is a large impact of the clarity of the wort added to the fermentor on the concentration of isomerized alpha acids (IAA), with a 30% increase in IAA for very clear wort and a 30% decrease in IAA for very cloudy wort.


      • Hop Cones vs. Pellets: IBU Differences
        This post presents results of five experiments that compare IBUs from cones and from pellets with all other conditions the same.  It finds that the increase in IBUs does not become greater with hop steep time, as would happen if the increase were caused by greater utilization or isomerization.  Instead, the increase is constant with hop steep time.  The amount of increase appears to depend on the hop variety.  In general, the IBU increase observed with pellets can be roughly modeled by doubling the production of oxidized alpha acids when hops are added to the kettle.


      • Why Do Hop Pellets Produce More IBUs than Hop Cones?
        This post first analyzes whether the increase in IBUs associated with hop pellets is more likely to be due to an increased concentration of isomerized alpha acids (IAA) or auxiliary bittering compounds (ABC). This analysis is based on the rate of decrease in IBUs and bitter compounds as a beer ages. It concludes that the increase in IBUs from pellets is most likely from ABC. Of the possible ABCs, oxidized alpha acids produced during the boil are the most likely source of the increase.


      • Two Pilot Studies for Maximizing Hop Flavor with Late-Hop Additions
        This post talks about two perceptual tests on hop flavor.  While results are not conclusive, it finds that (a) with the kettle uncovered, a 1-minute steep time yields more hop flavor than longer steep times, and (b) with the kettle covered, there is likely no perceptual difference between steep times from 1 to 15 minutes.  These results suggest that hop flavor is quickly lost through the evaporation of hop oils.


      • IBUs and the SMPH Model
        This post gives an overview of a new model for predicting IBUs, called SMPH. It also addresses some common misconceptions about the IBU.

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