Off Color Brewing

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Eille Biere de Miel

Biére de Miel, literally "Honey Beer", is a relatively obscure cousin of saison and Biére de Guard with the addition of honey which both boosts the alcohol level and drys the body. So lets talk a little about honey.

Chemically, honey is primarily an aqueous blend of carbohydrates consisting of mostly simple sugars including fructose (38.2%), glucose (31.3%), maltose (7.1%) and sucrose (1.3%). It's also delicious. Fructose and glucose are monosaccharides and thus considered simple sugars. These monosaccharides can be bonded together to form more complex, longer chain sugars. In brewing, the most important of these are sucrose (a disaccharide of glucose and fructose), maltose (a disaccharide of two glucose molecules), and maltotriose (a trisaccharide of three glucose molecules). Anything longer than maltotriose is considered a dextrin and is unfermentable by typical brewing yeast. During the mash, different saccrification enzyme systems break starch (thousands of glucose molecules chained together) into smaller sugars. The temperature of the mash determines which saccrification enzymes are most active this is our primary control point of the relative proportions of these different sugars in the wort. When we go and add a whole mess of honey we're changing this natural balance of sugars radically and this affects our fermentation greatly.

The addition of a high proportion of simple sugar creates an even more robust fermentation which boosts the temperature and volatility of fermentation considerably. While the increase in temperature can create higher levels of ester production, the vigor will scrub out a large proportion of the aromatics from the honey  leaving very little flavor impact from a very expensive ingredient. There are a couple techniques brewers can use to mitigate this. We could easily turn the fermentor's cooling jackets on for the first 48 hours to allow the beginning of fermentation to occur in a controlled environment and then turn them off to let the beer warm to the elevated temperature needed to create the desired ester profile and level of attenuation. It'd be a super simple fix, however, there is also a second issue.

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High concentrations of simple sugars in wort can slow or retard complete fermentation due to catabolite repression - a process whereby microorganisms will inhibit the production of carrier enzymes to preferentially uptake a particular type of sugar. Yeast's primary purpose of fermentation isn't to make us beer (because they're jerks) but to create energy through the decarboxylation of pyruvate to acetyl-CoA as a method to regenerate ATP. Alcoholic fermentation is already a less efficient method to do so as compared to aerobic respiration so to get a leg up on the process yeast will block the permease enzymes for more complex sugars. Cells do this in order to not expend the energy necessary to transport complex sugars through the cell wall and breaking them into their simpler component sugars when those simple sugars are already available. In high worts with high levels of simple sugars yeast, by the time yeast have fermented all of the simpler sugars they are worn out, used up much of their nutrient reserves and will only very sluggishly uptake and breakdown maltose and maltotriose. In extreme cases they can actually lose the ability to create the permease enzyme altogether and will be unable to fully ferment the beer.

When yeast is harvested and pitched while still in an highly active state, such as in the case of true top cropping, catabolic repression is less of a concern. If, however, yeast is cold crashed and harvested while in a dormant state (as typical when using cylindroconical fermentors) we have to take some measures to avoid this. There are some fancy things we could do but the simpler method is to just adding the honey after the onset of fermentation when the yeast is already in a highly active metabolic state and better able to deal with the abundance of fructose and glucose without compromising the complete attenuation of the beer. So yeah, we just do that.

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