Strawblog: Day 3: Disaster strikes?

Everything was set. The yeast were happy, I had the airlocks on so that any spare CO2 would bubble out, and so that nothing would explode.

When I woke up the next morning, though, I discovered that my explosion-prevention strategy had a slight flaw.

I woke up to this:

Strawberries. Everywhere.

Turns out some strawberry pulp had made its way up the necks of the growlers and lodged itself into the airlock, producing a plug of strawberry slop. Eventually, the pressure built up inside and popped the stoppers, sending sweet, sticky strawberry pulp everywhere within about a 5-foot radius of my fermentation area (read: the kitchen counter). It almost hit the ceiling, as did Sarah when we woke up at 7 am to find strawberry slurry everywhere. The cap from one of the airlocks was later found on the other side of my apartment.

It turned out that I didn’t lose too much juice, so I cleaned everything up the best I could (luckily the walls and cabinets are white, so a little bleach worked nicely) and set the airlocks back in to continue fermentation, which, not surprisingly, was proceeding vigorously. Check out the bubblage in the video (you may have to tilt your head 90 degrees left to get the full effect). I sound a bit stoned, but I’m really just in awe of science.

By the way, fermentation comes from the Latin fervere, meaning “to boil”. Looking at a fermentation in progress, it’s not surprising that the Romans would think that’s what was going on. And I guess that technically, CO2 is escaping the surface tension of the liquid, so I guess in a way it is boiling… but I digress.

Science!
When Jean-Claude Antoine Chaptal discovered the relationship between sugar and CO2 in a fermentation, he solved a very big problem in Champagne. Knowing the exact amount of sugar to add to a secondary fermentation saved many, many bottles from exploding. So how much CO2 is generated from the sugar in a fermenation? Remember high school chemistry? No? Well buckle up because you’re going back to Mr. Burcik’s class.

OK, remember our master chemical reaction of fermentation?

sugar (C₆H₁₂O₆) –> 2 CO₂ + 2 alcohol (C₂H₅OH)

That means for every molecule of sugar turned into alcohol, 2 molecules of CO2 form and escape from the liquid in the form of carbon dioxide gas. Let’s say that I had been really dumb and sealed the vessels completely instead of allowing for the CO2 to bubble out. Also, for simplicity, let’s neglect the CO2 dissolving in the wine in the container (that gets complicated), and assume that CO2 is an ideal gas (not a great assumption but we’re not teaching thermodynamics here…yet). Some of these values are what we engineers call “engineering estimates”.

***Warning: Chemistry and Math ahead. If you just want to know if the thing will explode or not, skip to the bottom***

Anyway, our must is at 23 Brix, which means that in one growler, there is about 345 g of sugar (1.5 kg of must).

345 g sugar is 1.9 moles (glucose is 180 g/mol), so we will produce 3.8 moles of CO2 in the growler. Not so bad right?

Remember the ideal gas law? At standard temperature and pressure, 1 mole of gas takes up 22.4 L of space. Well, inside this vessel, the pressure will be anything but standard, and the temperature is 25C, not 0C. A little PV = nRT and we find that this gas wants to take up about 96 L when it is confined to about 2 L of growler. That means the pressure in there will go up to about 48 atmospheres. That’s about 20 times more pressure than in car tires.

If the container were at 48 atm and suddenly failed, the energy contained in the resulting adiabatic explosion would be V*ΔP = 2 L * (48 atm – 1 atm [atmospheric pressure]) = 9.5 kJ, which is the equivalent of 2.2 grams of TNT. That may not sound like much, but after searching some sites that in retrospect are only quasi-legal, I found out what 2 grams of flash powder (more or less equivalent to TNT in explosive energy, Vermeij et al., “Morphology and composition of pyrotechnic residues formed at different levels of confinement”, Forensic Science International, 2009) can do.

(Note: I am not dumb enough to have actually done this. There are lots of explosion videos on YouTube, though, and it’s not really that suprising.)

The bottom line is be careful with fermentations! I’m not saying don’t try this at home, (in fact, I hope I’m encouraging it!) but don’t seal off your fermentation, whatever you do! The growler would probably have broken around 4-5 atm anyway, so I wouldn’t have to worry about an M-80 (~2.5 g TNT equivalent) going off in the kitchen. In either case, though, I’d have a much bigger mess.

Extra credit: Using the above calculations, how much pressure does a fermenting champagne bottle get up to? Hint: secondary fermentations in 750 mL bottles are usually dosed with about 20 g of sugar.

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Strawblog: Day 2 continued: Fermentation prep

So once I had the must chaptalized, it was (finally) time for some fermentation.

Forget Listerine, Devil's Springs is 160 proof, enough to sterilize pretty much anything. Also, don't take a sip by accident. Your face might melt right off.

Before starting fermentation, I wanted to make sure that my fermentation was clean, and that means sterilizing. Most wineries would sterilize using steam or detergents and sanitizing agents. While these are available for homebrewers (B-Brite and C-Brite are common sanitizers), I chose a different method of sterilization. I usually use Devil’s Springs double strength vodka to make boilo, a family recipe for a hot beverage served around the holidays (I’ll probably post a recipe around that time), but in this case it has another use. It’s 80% alcohol (ethanol), which is slightly above the 70% ethanol we use in lab to sterlilze ad disinfect our benchtops. I put some of this into all the bottles, hoses, growlers, and airlocks I plan to use for fermentation. Usually before I add anything to the must (hydrometer, for example), it gets treatment with regular vodka. Ask any commercial winemaker and they will tell you that about 90% of their job is keeping things clean and sterile.

When I picked the fruit it had been raining for two weeks beforehand, leading to a lot of damaged and mushy fruit (i.e., growth of fungus). I also wanted to curb the growth of any bacteria or other microorganisms which would like to feast on my sugary must. So I added some sulfur dioxide. Sulfur dioxide is an antimicrobial and antioxidant agent. The various forms of SO₂ are known as sulfites, and have been used in winemaking for thousands of years. Molecular SO2 is the actual antimicrobial agent and its concentration as free molecular SO2 depends on pH and several other factors. I can’t really measure the pH of my must at the moment so I took a suggestion from the Handbook of Enology (Ribereau-Gayon et al.), a famous winemaking textbook by many of the premier enologists in Bordeaux, and added about 40 ppm SO2 to the must (1/2 tsp of some of the 50 g/L SO2 that I swiped from my winemaking class. Don’t tell Ramón.)

I also added some tannin for color stabilization. Strawberries don’t contain that much tannin, and tannin helps to stabilize color in the long term by binding to color compounds called anthocyanins. In the long-term, co-pigmentation of tannins and anthocyanins stabilizes and contributes to color. Will the 1/2 tsp of {tannin} contribute? Probably not, since this wine probably won’t be around long enough for many co-pigmentation reactions to occur. It’s worth a shot, though, and the tannin may contribute some {astringency}, which I fear untreated wine may lack. The must certainly isn’t too astringent.

Another addition I made was Fermax, a yeast nutrient containing diammonium phosphate, which provides nitrogen to the fermentation. Nitrogen is an essential component to a fermentation because yeast need it to make amino acids, which are the building blocks of the proteins and enzymes the yeast need to manufacture in order to grow.

The last task was to get the yeast ready for their delicious meal. I got out my packet of Lalvin EC-1118 yeast (enough for 5 gallons) and sprinkled out a small portion of the packet. EC 1118 is a yeast isolated from the Champagne region* and for various reasons is the yeast of choice for ciders and fruit wines, as well as for sparklers. The yeast comes dehydrated and needs about 15 minutes in luke-warm water to rehydrate and reanimate. To make it as nice as possible for the yeast, I also warmed up the must by floating the mixing bowl I was storing everything in in warm water while the yeast were rehydrating. After 15 minutes, the yeast went into the strawberry must. I poured the mix into two growlers and attached the airlocks (filled with rum). Let the fermentation begin!

By the way, I obtained most of my supplies for this endeavor (yeast, Fermax, pectinase, sorbate, tannin, hydrometer) from the Ithaca Beer Company, which has many resources for home winemaking and brewing, includiny carboys, malt, recipes, hops, and lots of other accessories.

Science!
In most cases, the yeast used to ferment grape juice into wine is Saccharomyces cerevisiae. EC1118 is actually a strain of Saccharomyces bayanus, a very closely related yeast. S. bayanus and its cousin S. pastorianus are often used in brewing. In reality, though, S. cerevisiae, bayanus, and pastorianus are so closely related that their taxonomies have varied. At first, bayanus was believed to be a subspecies of cerevisiae. Nowadays, they are largely considered a species complex, and the difference between them seems largely academic. (Raineri et al., “Saccharomyces sensu stricto: Systematics, Genetic Diversity and Evolution”, Journal of Bioscience and Bioengineering, 2003)

Strawblog: Day 2: Chaptalization, or the boring math part.

When we last left our berries they were cold-soaking overnight in the fridge after crush and pectinase treatment.

Hydrometer, zoomed-in

The next day it was time to take some measurements. I squeezed the pulp in a hop bag to get straight juice out into a graduated cylinder. I suppose you don’t need a graduated cylinder but the amount you measure has to be deep enough to fit a hydrometer. The hydrometer, pictured right, correlates density of the mixture to height, which is related to the amount of stuff dissolved in there. The density can be converted to Brix (named after Herr Brix, reputed to have invented the hydrometer and the formula which converts specific gravity (i.e., density) to percent sugar), which is a measure of soluble solids per 100g of solution, or more simply, percent sugar. A reading of 20 degrees Brix corresponds to 20 grams of dissolved solids per 100 g of solution.

(NB: Brix is not necessarily a measurement of sugar, however, in a given {must}, 90-95% of dissolved solids are fermentable sugars. Others include non-fermentable sugars like arabinose and xylose, organic acids, polyphenols, etc. )

Hydrometry on the juice, with graduated cylinder for extra science-y goodness.

The strawberries came in at 7 Brix, which is 70g/kg and the must is about 2.88 kg (estimated from the density), so we’ve got about 202 g of sugar. If I were to ferment this as is, I’d have the alcoholic equivalent of strawberry light beer. We’re making wine here, not Arbor Mist. Let’s up the ante a little, shall we? More sugar means more alcohol.

Let’s say I want to chaptalize (i.e., add sugar to the must, named after Monsieur Chaptal, who discovered the relationship between sugar and alcohol in wine) up to 20 Brix. How much do I have to add? ALGEBRA!

202 + x (g sugar)
——————— = 0.2 (g/g); x= 467.5 g sugar
2880 + x (g total)

Unlike Alton Brown, I don’t have a scale in the kitchen, so I have to work with volume. According to sugartech.com , the density of bagged white sugar (sucrose) in 700g/L = 165 g/cup. So to get up to 20 we need 2 5/6 cups. Let’s make it an even 3.

From strawberry juice to strawberry syrup. I think I underestimated the volume.

I added 3 cups sugar. If this were Beaujolais, I’d be locked up. Just as a check, I took the Brix measurement again. Whoops, the final Brix was 26! I guess I underestimated my volume of must. Apparently I did, because when I filled up the growlers I had about 3 quarts instead of the gallon that I thought I had. I didn’t want too much headspace on the wine so I topped them up with some cherry juice (no preservatives…) I had on hand. After this addition, the final Brix reading was 23. Depending on what formula you use (and the yeast), that should lead to an ABV of 12-13%.

Science!
During fermentation, sugars such as glucose and fructose are converted into carbon dioxide and ethanol in the following reaction:
C₆H₁₂O₆ –> 2 C₂H₅OH + 2 CO₂
This means the theoretical yield for ethanol on a per mass basis is about 0.51 * sugar, or ~62% on a “by volume” basis. This doesn’t really happen and often the Brix to ABV conversion is more like 0.55. Why? Some of that sugar goes into yeast biomass, some of it becomes glycerol, and some alcohol is carried away by CO₂… More on CO₂ next time, when we prepare to start fermentation…

PS I know what you’re thinking… I added sucrose, which is C₁₂H₂₂O₁₁ ! That doesn’t fit into the formula! Luckily for me, yeast produce an enzyme known as invertase, which converts sucrose into its constituent monosaccharides, fructose and glucose, both of which are C₆H₁₂O₆ and both of which are easily consumible by yeast. It’s also what they add to chocolate-covered cherry cordials to make them all gooey on the inside. (The invertase breaks down the sucrose-saturated fondant into fructose and glucose.)

Bonus question: If I had 3 quarts of 26 Brix juice and added 1 quart of cherry juice to bring it to 23 Brix, what was the Brix of the cherry juice?

Strawblog: Day 1

Sarah and I are members of the Sweet Land Farm CSA (community-supported agrictulture) in Trumansburg. For those unfamiliar with the CSA concept, you basically invest in a share of the farm and your dividends are vegetables and fruits. Anyway, one of the benefits of membership is unlimited U-Pick strawberries. Naturally, I picked about 5 quarts of berries and decided to make them into wine. It then occurred to me that I could document my winemaking process and drop some winemaking knowledge bombs along the way. So, here goes.

(NB: Strawberries aren’t technically berries, they’re “accessory fruit“, since the edible part is not generated from the ovary of the plant, but surrounding tissue. Grapes, however, are berries.)

Harvest: I tried to pick fruit that wasn’t at all mooshy or damaged by mold, since molds often produce enzymes that do unsavory things to wine. For example, {botrytis} produces a lot of the enzyme laccase, which oxidizes polyphenols in fruit juice to make browning products, and unlike other polyphenol oxidases, is resistant to inhibition by sulfites. (Dewey et al., “Quantification of Botrytis and laccase in winegrapes”, AJEV, 2008). Avoiding soft fruit was difficult since it has rained here on and off for about the past two weeks. Also, strawberry plants are low to the ground and the leaves hold water like bowls, so it’s a pretty wet environment.

The destemmed fruit

Destemming: I manually destemmed all the berries, so as not to have stemmy, vegetal aromas like methoxypyrazines (bell pepper, peas) around.

Crush: This was the fun part. I crushed the berries with my (clean) hands, squishing them between my fingers. The hearts of the fruit are kind of hard, so eventually I switched over to a potato masher. What I ended up with was basically strawberry stew, with solid matter still pretty much outnumbering the straight-up juice. To rectify this, I added an enzyme called pectinase.

Pectin is a polymer of sugars, kind of like starch (amylose)

Enzyme treatment: Pectinase You’re probably familiar with pectin. It’s the powder you add to pretty much any cooked fruit to take it from fruit slop to jelly or jam. Pectin is a polysaccharide (bunch of sugar molecules bonded together) that is found in the cell walls of plants. Apples and citrus fruits have a lot of pectin, but grapes and strawberries also have some. Pectinase, a standard winemaking treatment to aid in {must} clarification, chops up the polymer into its constituent sugars, thinning out the liquid and aiding in separation.

Cold Soak: I actually neglected to pick up some yeast before I got started, so I decided to put the {must} in the refrigerator overnight. The purpose of this was two-fold. One, I didn’t want it to start fermenting with the natural yeasts (including undesirables like Kloeckera). Second, cold-soaking whole or crushed grapes has been shown to aid in extraction of anthocyanins (color compounds), adding some color to some wines (Gómez-Miguez et al., “Evolution of colour and anthocyanin composition of Syrah wines elaborated with pre-fermentative cold maceration”, Journal of Food Engineering, 2004), though the jury is still out on its effectiveness. It’s become clear to me that I am going to treat this like a red wine.

Up next: Starting fermentation….