Fermentation Kinetics

Since I "re-started" the fermentation in the mead about three weeks ago, I have kept an eye on the fermentation rate. It seems to be going as one would expect: after the large increase in bubble rate over the first 2-3 days, the bubble rate has been decreasing slowly. As a chemist, in this sort of situation, I can't keep myself from taking measurements and recording them in a table. For many years, in all sorts of chemistry experiments, I measured and modeled chemical kinetics (i.e. the study of the rate of reactions). Here's what I found about the mead fermentation.

Method: Measure the number of airlock bubbles per minute, noting the time and date. Calculate the logarithm of bubble rate, and make a plot of this against time.

This is what is known as a "first order plot". It shows that the rate does not decrease linearly, but that the rate of decrease slows down with time. This is typical of reactions in which the rate depends on how much of the starting material, or reactant, is present. In the case of fermentation, the reactant is sugar. As sugar is consumed by the yeast, the rate of fermentation will obviously decrease. However, the decrease in rate is not linear - the "deceleration" slows down over time. In this type of reaction, when you make a graph of the logarithm of the rate vs. time, you get a straight line. That's what happened here.

Fermentation kinetics are actually a lot more complicated, especially at the beginning of the fermentation process, when yeast populations are growing, and the fermentation rate is accelerating. In this case, fermentation is almost complete and the yeast population is no longer growing. There are lots of yeast cells present, and the rate is only limited by the amount of sugar remaining. The result is "first order kinetics".

One day, I would like to try measuring the fermentation rate from start to finish, but it gets complicated. Measuring airlock bubble rate would be a pain during primary fermentation, when the rate is quite high. The other way you can measure the rate is by looking at alcohol content. The problem with alcohol content is that the measurement is in situ, requiring the insertion of a wine thief and hydrometer into the must. This increases the likelihood of introducing oxygen or microbes into the must.

  

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!

Peach Melomel

For a couple of years, I have followed home winemaking posts about small batches of melomels. A melomel is simply a mead amended with some kind of fruit. You can use any kind of fruit you want. The resulting mead will have a mix of honey and fruit flavours.

I had some good honey leftover from the most recent batch of mead, and we had some fresh fruit from British Columbia, including some very juicy, perhaps even overripe, peaches. This presented an opportunity to try making a peach melomel, which struck me as a potentially nice combination.

Here's the recipe I used:

- 10 L of filtered water
- 3 campden tablets
- 2 tsp yeast nutrient
- 1 tsp peptic enzyme
- approximately 3 kg honey
- 1 cup of sugar*
- 11 pitted peaches, sliced
- packet of Lalvin EC1118 yeast

*Sugar was needed because the dissolved honey only gave s.g. = 1.078. The sugar brought up the s.g. to 1.086.

After mixing up all the ingredients except fruit and yeast in my primary fermentation bucket, I put the peaches in a nylon straining bag, tied it off, and squeezed the peach juices into the must. The amount of peach juice was surprising. I put the whole bag of strained peaches into the must and let it sit for 36 hours. After removing the bag, I sprinkled yeast on the surface. A few hours later, fermentation was going strong.

Fermentation "head" on the peach melomel

After six days of primary fermentation, the 'head' had collapsed, and s.g. = 1.024. I transferred to a sterilized 3 gallon carboy for secondary fermentation.

Peach Melomel in Secondary.

Unfortunately, these pics don't really show the subtle peachy colour of this melomel. I'm looking forward to seeing how the colour turns out after it's aged, clarified, and bottled.

Beeswax?

Back to the mead...

Four weeks ago, I racked the mead into a carboy, to allow secondary fermentation to proceed, which it did. Fermentation was more or less over a couple of weeks ago Tonight, I decided it was time to rack the mead into a clean carboy so the mead can bulk-age, lose CO₂, and clear up.

During secondary fermentation, there was a small froth on the surface, which isn't a big deal. However, as fermentation slowed down, a fine, beige solid remained on the surface of the mead, and along the inside, top surface of the glass, under the neck. The solid never dissolved.

Beeswax?

After racking, I managed to swipe my finger into the dirty, empty carbon, and get some of this material. It was granular, hard, but seemed a bit 'gummy', like paraffin wax. Question for honey and mead people: Is this beeswax?

This particular honey is not heavily processed. I used 2-3 kg of honey, so it wouldn't be a surprise if there was a small amount of beeswax in there.

Sadly, before I could measure specific gravity, I dropped my hydrometer on the floor. So, I cannot estimate alcohol content of the mead right now.

The mead sure tasted good, though. I was surprised by the sweetness. Fermentation was OVER. There shouldn't be any residual sugar in there. It could be that there are other sugars (e.g. pentoses or something like that) that the yeast did not touch. This deserves some research. Question for honey people: what types of sugar are present in honey? 

Apple Cider 2016

The last time I made cider (see post here), I was failed by EZ Cap bottles, which just didn't hold any pressure. This resulted in a batch of still cider. Still cider is fine, but I aspire to make carbonated, homemade cider. One of the reasons I wanted to make homemade beer was to get beer to carbonate in the bottles, using standard bottle caps. That worked out just fine (see Festa Brew "Continental Pilsner). So, it was time to revisit cider-making, and attempt natural carbonation in the bottles.

Tanya and I picked the apples off of our tree, and made the fatal decision that there were enough apples that we could simply cut them up by hand before pressing. That was crazy - the manual labour to cut up all of our apples up into eights (or smaller) was just too much. Next time, I'm going to obtain a fruit crusher like last time.

The pressing however, went fairly well, and we obtained approximately 4 gallons of apple juice. The specific gravity of the apple juice was 1.034, which was almost identical to juice from the last time we pressed apples. To this, I added 4 crushed Campden tablets, 2 tap. yeast energizer, and 1 tsp. of peptic enzyme. After 24 hours, I added a packet of Lalvin EC1118 yeast, by sprinkling it on the surface. Fermentation was well underway a day later.

Primary fermentation proceeded quickly. Four days after adding the yeast, the foam on the surface had collapsed and it was time to transfer to a carboy. The volume (4 gallons) created an opportunity for two separate batches. I siphoned the bulk of the cider to a 3 gallon carbon and placed an airlock on it. This batch is meant to be regular cider.

Spiced Cider

The remainder (which amounted to a little over 1/2 gallon) went into a 1 gallon jug which I topped up with distilled water to which I had added 1 cup of sugar. This was done to get the alcohol level up to where it should be. If I did not add any more sugar, this would have been a 1:2 dilution, and the cider would be very weak). I also added 1/4 tap of nutmeg and two cinnamon sticks for flavour. I sealed the jug with an airlock.

Regular cider (left), and spiced cider (right). Fine solids are settling out.

After four days in the carboy, fermentation of the regular cider was virtually complete, and the bulk of the fine solids had settled. It was time to add priming sugar and bottle! So, I siphoned the cider to a large pail, added 3/4 cup of dextrose, stirred thoroughly, and bottled it just like you would beer. The yield was 4 x 1 L bottles, and 22 x 330 mL beer bottles.

I bottled the spiced cider one day later, adding 1/4 cup of dextrose to the (approx.) 1 gallon of spiced cider. Yield was 10 x 355 mL bottles.

A taste test of the spiced cider revealed a beverage that tasted like Christmas. The nutmeg and cinnamon paired well with the apple and the little bit of sweetness from the priming sugar. It remains to be seen how the spices affect the taste when the cider is carbonated and dry. I can't wait!

According to the purple "Winemaker's Recipe Handbook", you should age the cider for three months!!! This seems like a long time. I might get impatient and open a bottle in a month or so, just to see how it's coming along.

Mead v.2

My first attempt at mead left me unsatisfied. Looking back, there were three things that I did incorrectly:

1. Failed to add yeast nutrient. Honey does not have the range of minerals and other nutrients that yeast require. Fermentation only really started once I added the yeast nutrient. Further, all of my  fussing around to get fermentation started would have introduced unwanted oxygen, which would have led to undesirable compounds that affect taste.
2. Starting specific gravity was too high at the beginning (1.120) and the end (1.019) of fermentation.This gave a mead that was sweet, heavy, and very alcoholic. The balance of taste wasn't right (and still isn't!).
3. Honey quality. A friend from my undergraduate days at university now runs a honey business, and she pointed out that Costco honey is rubbish - if I want to make good mead, I need to start with quality honey. ("Okay. Point taken.")

So, it is now over two years after my first attempt at mead, and I finally got around to my second attempt. This time, I'm not making any of the mistakes I made the first time.

We have a great farmers market in St. Albert, and there are always three or four honey producers there. My wife and I went shopping one Saturday morning and obtained 7 kg of unpasteurized, local honey for $50. The vendor was Good Morning Honey Ltd.

Mead recipe:

3 Campden tablets
2 tsp yeast nutrient
10 L distilled water
Honey
1 packet of Lalvin EC-1118 yeast

Campden tablets and yeast nutrient were added to the water in the sterilized primary (bucket). Honey was added, with stirring, until s.g. = 1.088. After 24 hours, the yeast was hydrated and added to the must. Fermentation bubbles were observed within one hour of pitching the yeast.

After four days in the primary, s.g. = 1.065. I decided to rack the mead to a carboy. Fermentation has continued since then (6 days ago).

Mead, after racking to carboy.

I think most chemists will know what I'm talking about when I describe this fermentation as "clean". What I mean is this: when chemists conduct a chemical reaction the lab, especially when they are trying to synthesize a compound, they strive for a "clean" reaction. A clean reaction is something we recognize easily from the absence of unwanted precipitates, the absence of guck on the sides of reaction flasks, the relative transparency of solutions, and colours that you want to see (e.g. you don't want to see your mixture turn brown when the product you want is colourless). These are simply physical clues that a reaction is going right.

This mead has been "clean" from the beginning: the colour hasn't changed, the liquid is as transparent as you could expect if there were only little bits of yeast and bubbles that were scattering light. You can tell that clarification is going to be a snap. And, there was hardly any foaming, which suggests a very pure honey (i.e. no surfactants of any kind - natural or artificial).

The plan is to let this mead ferment all the way to dryness and then I will rack it and let it bulk age in a carboy for a couple of months. I'm looking forward to enjoying some of this mead over the Christmas holidays.

Festa Brew "Continental Pilsner"

So, I made beer earlier this year. However, this wasn't "hardcore" beer making. I started with a Festa Brew kit that my local Wine Kitz store sells. The store happened to have a sale on kits, so I bought one for $60.

A Festa Brew kit consists of a 23 L bag of pasteurized wort, a packet of yeast, and instructions. In beer making, the messy and complicated part is the wort preparation. If you don't have to make your own wort on the stove-top, you get to avoid all the mess of splashing sticky wort all over your stove and kitchen, and the anxiety over getting temperature control exactly right. A Festa Brew kit, then, is kind of a "Fisher-Price" version of a beer kit. Sounds like an easy way to make your first beer, doesn't it?
 

Festa Brew kit - A box of wort, a packet of yeast, and some instructions.

As it turns out, it really is easy if you follow the instructions. In essence, the instructions are:

1. Transfer the wort into the primary (white bucket)
2. Add yeast.
3. Loosely close lid on primary and wait 5 days.
4. Transfer wort to secondary with air lock. Wait a week.
5. Transfer wort back into a bucket and stir in some dextrose (sugar).
6. Bottle.

Wort in secondary.

23 L (5 gallon) of wort is a lot of beer. The yield on this kit was 40 bottles (330-mL recycled Stella Artois bottles) and 8 1-L growlers. After two weeks of fermentation IN the bottles (for carbonation, of course), the beer was ready to sample.

On sampling, I wrote in my notebook: "This is a good beer. Similar to Stella, but has more flavour - darker, more of the caramel sorts of flavours as opposed to hops. Hops are mild."

Cheers!

This kit was a little too easy, and I'm eager to try making beer the hard way next time (i.e. make my own wort). On the other hand, there is something nice about a kit that is just that easy. All you need is the basic set of wine-making equipment (bucket, carboy, airlock, siphon...) and some recycled beer bottles and you're ready to go. Bottle capping was easy because the Wine Kitz store loaned me the bottle capper. I plan on purchasing my own capper for future beverage projects.

Bulk Aging

Until recently, I have not bulk-aged my wines prior to bottling. Rather, I simply followed wine kit  instructions that tell you to wait for secondary fermentation to more-or-less come to an end, add finings, rack, and bottle. The whole process from opening the kit to bottling takes only a few weeks. There is no bulk aging.

After going through the "wine kit" process (without bulk aging) several times, I observe two main problems with wines made this way:

1.  Carbonation

Fermentation produces a lot of CO₂. Where does it go? CO₂ is dissolved in the wine until it reaches saturation. After that, CO₂ bubbles out of the wine into the air. When fermentation ends, there is still a lot of dissolved CO₂ in the wine, and it takes time to move into the gas phase. One way to release CO₂ is to agitate the wine (e.g. by stirring). Another way to get rid of it is to just give it time to gradually escape through the airlock.

If you don't give it time to escape before bottling, some of the CO₂ stays dissolved in the wine. All of my non-bulk-aged wines have a level of residual carbonation that detracts from the enjoyment. It's not much, but the carbonation is noticeable on the tongue. Who wants a tiny bit of fizz in their red wine?

Over the Christmas holidays, we opened up a bottle of a raspberry wine from a local winery. To our surprise, this wine contained more CO₂ than any of my homemade wines. The wine  released bubbles right there in the wine glass, just like sparkling wine. (And, no, it wasn't meant to be a sparkling wine!) The winery had probably bottled the wine before the CO₂ could escape. Fizzy fruit wine!

2.  Sedimentation

Finings do not remove 100% of the particulates from wine. Every time I used finings without bulk aging before bottling, a small amount of sediment has always appeared in the bottle. It usually takes a few months, but it's there and it spoils the appearance.

Sediment in rhubarb wine

An obvious way to prevent this from happening is to just let the wine age in a carboy (with an airlock) for a few months. By then, virtually 100% of the sediment should have crashed out in the carboy. By the time you bottle the wine, it should not be throwing any more sediment.

I have bulk-aged my most recent wines (two versions of Dragon Blood) and will write a separate post on them. Early observations are that the bulk aging solved the carbonation problem. I'm hopeful that there won't be any sedimentation in the bottles.