Stuck Fermentation

What is it about mead and stuck fermentation? If you google search "mead stuck fermentation", you find that this is a widespread problem for home mead makers. I recently had to deal with it in my most recent attempt at mead.

Back in August, secondary fermentation of this mead had more or less stopped. Things had been going pretty well, and I assumed that most of the sugar must have been used up by the yeast. As I noted in an earlier post, I broke my hydrometer and therefore had no quick way to measure the specific gravity. (Actually, I could have measured out a volume of mead and measured the mass, from which you can easily calculate density. I have a cute little jeweller's electronic balance that measures to 0.01 g.) So, without knowing the completeness of the fermentation, I racked the mead with the intention to let it age and clarify.

As the mead was "aging", I noticed that there was a constant, very slow rate of gas production in the carboy. In the meantime, the batch of peach melomel was getting to the end stage of secondary fermentation, and it was time to rack it. Last week, I decided to rack the melomel and the mead, checking the specific gravity of each using my new hydrometer. Here's what I found:

Peach Melomel s.g. = 0.990 (Conclusion: fermentation is complete, and it's time to let it age)

Mead s.g. = 1.038 (Conclusion: oh crap, fermentation is stuck)

So, I had to intervene. I added two Campden tablets (crushed and pre-dissolved), 1 tsp of yeast nutrient, and a packet of Lalvin EC-1118 yeast. Bubble formation seemed to pick up within a few hours. The next day, gas production still wasn't as fast I would like, so I raised the temperature in the room using an oil heater, and also added 2 tsp of yeast energizer. Yeast energizer has a slightly different nutrient mix as yeast nutrient. Three days later, the fermentation in the mead was chugging along nicely, and continues:

Gas production after kick-starting the fermentation

with yeast nutrients and higher temperature.

Did fermentation resume because of added nutrients for the yeast, the higher room temperature (from 17 up to 22 degrees C), or both? I don't really know, but I suspect it was mostly the nutrients. After all, the peach melomel, which presumably had more nutrients from the peach juice, seemed to work out fine in the relatively cool room in which I keep this stuff. Lesson for next time: add more nutrient, with the proviso that "yeast energizer" is likely the more effective.

Prohibition, Temperance, and Pseudoscience

This post deviates a from my normal blog topic (making alcoholic beverages). Why is prohibition important? Well, Alberta still has legislative and regulatory "quirks" that are holdovers from the days of prohibition in Alberta. For example, in home winemaking, there is no legal way for a wine kit supply store in Alberta to provide customers with a clean, physical space inside the store in which to make wine, store it as it ferments, and bottle the wine when it's ready. These services are popular in other provinces, but are not allowed in Alberta, because such a service goes beyond "home winemaking". Governments in Alberta are liberalizing the liquor laws, but there is a long way to go. An interesting documentary account of the history of beer in Alberta, including the impact of prohibition, can be found at: Aleberta

Some time ago, I was surfing through the photo collection of the Provincial Archives of Alberta, and came across a bunch of old "Temperance posters". These posters were published by "The Dominion Scientific Temperance Committee", which, I gather, was an arm of the Women's Christian Temperance Union back in the days of prohibition. Some of these posters are quite amusing:

Provincial Archives of Alberta, Object number PR1974.0001.0400a.0001

Provincial Archives of Alberta, Object number PR1974.0001.0400a.0006

It is not clear to me what phagocytosis (the white blood cell "swallowing and digesting" germs) has  to do with alcohol consumption. Clearly, the idea was to scare people away from consuming alcohol, and, I suppose, get them to drink water instead.

The next poster piqued my interest because it touches on some chemistry.

Provincial Archives of Alberta, Object number PR1974.0001.0400a.0002

The poster argues that the nutritional value of grape juice is much greater than that of wine, but the numbers don't make a lot of sense. The only number that looks correct is the 20% "food value" of grape juice. That number roughly corresponds to the percentage (by mass) of sugar in grape juice. However, the percentages of water, alcohol, and "food value" in wine do not make sense.

1) The water content of wine is a lot higher than 78%. Water is a by-product of the fermentation of sugar. So, during fermentation, sugar decreases, and the proportion of water and alcohol increase.

2) The poster gives 17.5% alcohol for wine. Is this 17.5% by mass or 17.5% by volume? On wine, beer, and liquor labels, alcohol content is usually listed as a percent by volume. 17.5% would be on the high end of percent volume for wine. This poster, however, seems to be using mass percentages. The mass percentage should be a lot lower, because the density of pure ethanol is less than that of water. So, there is something funny going on.

3) The food value of wine is listed as 4.5%. Sure, wine contains residual sugars and other organic components that have nutritional value, but this number appears to have simply come from subtraction: 100 - (78 + 17.5) = 4.5. But, as the percentages of water and alcohol are suspect, so is the 4.5% value.

4) The poster implies that alcohol has zero food value, which is incorrect! The caloric content of foods and beverages can be determined through calorimetry: In the good old days, a scientist would combust a sample of food in a sealed chamber and measure the amount of heat produced. Calorimetry is a lot of work, so nowadays, the caloric content of foods is determined indirectly using the "Atwater system" (Scientific American has an article on this, here). Basically, this involves adding up reference caloric values for different components of the food or beverage in question. The reference caloric value of carbohydrates (including sugar) is 4 kcal/g (1 kcal = 1 food Calorie). The reference value for alcohol is... wait for it... 7 kcal/g! (Yes, on the basis of mass, alcohol has more food Calories than sugar.) So, the poster is WRONG.

The web site Compound Interest has a lot of neat infographics about various familiar substances. Take a look at their infographic on red wine. Their numbers make a lot more sense (86% water, 12% alcohol, 2% other organic compounds).

By the way, the "food value" of a 5 oz. glass wine is around 125 Calories, which is equivalent to 25 jelly beans. The glass of wine is arguably the healthier option of the two!

These temperance posters were published ca. 1912. Are these scientific mistakes forgivable, given that they were made over 100 years ago? Not really. Even in 1912, physics and chemistry were sufficiently advanced that mass and volume compositions were well understood and measured reliably. And, calorimetry was already an established experimental technique in the field of thermodynamics, which had its heyday in the age of steam engines. What's going on here is the twisting of information to support a particular agenda. It's pseudoscience!