The Chemistry of Metabisulfite and Sulfur Dioxide in Wine.

TRIGGER WARNING:  I assume that the reader knows a couple of things about chemistry.  If you are little rusty in your chemistry knowledge, here are some quick tips:

• Sulfur, oxygen, and hydrogen atoms are given the symbols S, O, and H.
• Compounds are groups of atoms that are bonded together.  The formula of a compound gives the type and number of all the atoms it consists of.  For example, the formula "H₂O" means that the compound has two hydrogen atoms and one oxygen atom.  Charges of ions are given as superscripts at the end of a formula  (e.g. SO₃^2-, which means one sulfur and three oxygen atoms with a negative two charge).
• In molecular structures, we show bonds between atoms with lines.  One line means a "single bond", two lines mean a "double bond", etc...
• To write a chemical reaction, we write the formulas of reactants, draw an arrow, and then write the formulas of the products.

OK, with that out of the way....

Potassium metabisulfite is ubiquitous in wine making.  It is the active component in campden tablets and can also be purchased in crystalline form at your local wine making supply store.  It is added to wine in order to produce sulfur dioxide, which is very effective at killing off unwanted microbes that can spoil the wine.  So, how does it work?

Metabisulfite is a complex anion (negatively charged ion) that consists of two sulfur and five oxygen atoms.  It has a -2 charge.  Generally, metbisulfite is sold as a potassium salt.  In potassium metabisulfite, the negative charge is balanced with two potassium ions (+1 charge each).  Sodium can also balance the negative charge.  However, sodium metabisulfite is not as common as the potassium form.  In terms of generating sulfur dioxide, it does not matter whether you use sodium metabisulfite or potassium metabisulfite - they both react the same way.

To see how metabisulfite is transformed chemically into sulfur dioxide, let's start by looking at the molecular structures of three compounds:

1.  Sulfur dioxide, SO₂.  The structure is relatively simple.  A sulfur atom is bonded to two oxygen atoms in a bent structure.

2.  Sulfite (SO₃^2-) and hydrogen sulfite (HSO₃^-).  These two chemical species are the principal forms of sulfite that exist whenever a sulfite compound is dissolved in water.  They are simply acid-base forms that interconvert with the addition or subtraction of hydrogen ions (H⁺).  That means that the relative amounts of the two depend on the hydrogen ion concentration, which is commonly measured as the pH.  At the pH of wine, which is, say, between 3 and 4, sulfite (SO₃^2-) only exists in minute amounts.  The most abundant form is hydrogen sulfite (HSO₃^-).

3.  Metabisulfite (S₂O₅^2-).  In the structure, it kind of looks like there is an SO₂ molecule attached to an SO₃^2- ion, with a bond between the two sulfur atoms.

When metabisulfite is added to water, it reacts immediately with water to generate hydrogen sulfite:

From a chemical point of view, you can think of the oxygen atom in H₂O "attacking" one of the S atoms (the one bonded to two oxygen atoms) to form a new sulfur-oxygen bond.  This breaks the bond between the two sulfur atoms and results in two hydrogen sulfite ions.  This may not be the exact mechanism (I have not looked it up), but it's a nice way to think about it.

Let's say you are making wine with a kit and the secondary fermentation is complete.  You just added the packet of potassium metabisulfite to your wine and you start stirring.  The reaction above just took place, and you now have a lot of HSO₃^- dissolved in your wine.

HSO₃^- reacts with H⁺ ions in the wine (remember, your wine is somewhat acidic) to form dissolved, "molecular" SO₂, which is written as SO₂^.nH₂O.  This means that SO₂ is "hydrated", or associated with water molecules, in solution.

This reaction is written as a chemical equilibrium, which means that at any instant, some of the compounds on the left are reacting to make compounds on the right, and vice versa.  This is why there are two reaction arrows.  After some time, the reaction comes to equilibrium, which means that the concentration of each compound stops changing.  At equilibrium, the relative concentrations of reactants and products are defined by an equilibrium constant, K, that is unique to the reaction.  For this reaction, K is written as:

Concentrations are indicated by the square bracket around each compound.  If you were to measure the equilibrium concentrations of SO₂^.nH₂O, HSO₃^-, and H⁺, entered the values in the expression above, and did the calculation, the answer would be 62.5.

If any of the concentrations change, then the concentrations of the other compounds must change over time so that the system comes back to equilibrium (and the expression again equals 62.5).  So, let's say you add an acid blend to your wine to change the flavour.  By adding acid, you have increased [H⁺], and the expression will no longer equal 62.5.  In order to get back to 62.5, the equilibrium must shift:  [SO₂^.nH₂O] will increase slightly; and [HSO₃^-] will decrease.  This is an important practical result.  The more acidic the wine, the more SO₂ will be produced from HSO₃^-.  Wines that are more acidic require less added metabisulfite.

At room temperature, SO₂ exists as a gas (not a liquid or solid).  Consequently, some of the SO₂ will be released as a gas.  This is one reason why, after adding metabisulfite to wine, you might observe bubbles coming out of the wine as you stir it.  Stirring can also release dissolved CO₂ that was produced during fermentation.

What happens to the dissolved, molecular SO₂ in the wine?  Several things:

• some of the SO₂ will become chemically bound to various wine components, like complex sugars.
• some escapes as a gas
• some stays free and dissolved, in equilibrium with HSO₃^-.

The goal is to have enough dissolved, molecular SO₂ in the wine to keep the microbes at bay.  Typically, 0.5 ppm SO₂ is needed for red wines, and 0.8 ppm is needed for white wines.  Commercial winemakers use analytical chemistry techniques to measure the SO₂ content in their wines.  This lets them make sure they meet regulations for the SO₂ content of wines that are sold on the market.  My wife, who is also a chemist, once had a summer job at a winery near Melbourne where she performed SO₂ assays, among other tasks.

The average home winemaker does not need to worry about measuring the SO₂ in their wines.  We can use a simple rule of thumb:  one campden tablet per gallon of wine will give you approximately the right SO₂ concentration.

For all the expert and amateur winemakers out there, I would love to know your thoughts on how much SO₂ is really needed in wines.  For example, in the book The Way to Make Wine, the author suggests adding campden tablets every time you rack your wine.  This strikes me as overkill.  On the other hand, some winemakers use none at all.  What is your experience?

Let me know if you find this useful, or, even better, if you have questions.  I will do my best to answer.

Merry Christmas!

Bibliography

Chemistry of the Elements, Greenwood, N.N. and Earnshaw, A., Pergamon Press, New York, 1984.

The Way to Make Wine, Warrick, S., University of California Press, Berkeley, 2010.

Wine Kit: Johannisberg Riesling

The last few months have been awfully busy at work and at home, and I have not had the time or energy for my fermentation hobby.  For almost 3 months, a CellarCraft Sterling Johannisberg Riesling kit has been sitting in my basement, waiting for me to open it.  Today, I started it.

First things first, being the kind of person I am, I was puzzled by the spelling of "Johannisberg" because I am more familiar with spelling of the city of Johannesberg, RSA.  It turns out that Johannisberg refers to the Schloss Johannisberg in the Rheingau region of Germany.  This is where the "late harvest" wines were, apparently, discovered.

Schloss Johannisberg

The wine kit itself is pretty standard.  It included two packets of bentonite clay, which is a fining agent.  As per the instructions, I mixed up the clay with hot water in the primary fermenter and then added the grape juice to it.  This is only the second time I have added a fining agent before the fermentation.  Why is this done?  Because the bentonite clay particles, which are negatively charged, react with positively charged particles in the wine, and these settle out.  This seems like a great way to remove macromolecules like proteins, which are a source of haziness in wines.

The following is a nice general review of fining agents and how they work:
A Clearer Understanding of Fining Agents



Image of Schloss Johannisberg:  http://commons.wikimedia.org/wiki/File:Johannisberg_Rheingau.jpg

Fruit Wine Blends

Let's face it - you can ferment just about fruit that you can pick out of the garden.  My favourite starting material (I am a chemistry after all) is Himalayan blackberry (Rubus armeniacus). The fruit is large and juicy, and if you don't mind getting scratched to hell, one can pick 10 lbs in about 90 minutes.

I generally pick/freeze at least 100 lbs every summer and put them in the freezer - along with the other fruits from my garden and our neighbours. Once fall comes, it is time for making wine!! The advantage of freezing the blackberries is that they break apart into mush upon thawing, making it easier for the fermentation.

Here's a rough schedule of a batch of blackberry wine I made in August 2012.

18 lb of frozen berries plus 1/2 tsp metabisulfite allowed to thaw in the primary fermentation container (which was first washed with Javex solution and well rinsed). This was on Aug 17th.

The next day, 2 Tsp yeast nutrient, 1 Tsp pectic enzyme, 1/2 tsp grape tannin and 2 Tsp acid blend was sprinkled on top of the fruit. A total of 15 lb of sugar was added, followed by sufficient warm water (~18 L - with stirring) to bring to total volume up to ~ the 5 gallon mark (the fruit will be floating at this point).

This gave me a SG reading (hydrometer) of ~1.090.

One package of wine yeast is then sprinkled on top of the pulp and allowed to sit (with a cover on) overnight. Depending upon the room temperature, the top of the fruit will be bubbling/frothing the next day and I then stir the yeast into the solution, and stir up the pulp twice a day after that.

I racked the juice off the pulp (on Aug 22nd) into the secondary fermentation container and added a bit of water to bring the volume close to the top of the container (watch out for frothing over the first couple of days) and put on an air lock (containing a bit of metabisulfite solution). The rate of bubbling gradually slows as the amount of residual sugar in solution decreases.

I racked the wine into another secondary fermentation container (containing a bit of bentonite and some gelatine) on Sept 18th and replaced the air lock.

On Oct 12th I racked the wine a final time and then bottled it

The final result was 29 bottles of a dry, full-bodied wine.

I have also included a picture of some of the various fruit wines I currently have aging. 

Feel free to experiment on your own …. have fun and happy sipping.

Fermenting Port Alberni grapes

Today I racked 4 batches of wine:
a) the juice from 57 lbs of green grapes
b) the juice from 45 lbs of purple grapes
c) the skins from the green grapes plus 5 lbs of blackberries
d) the skins from the purple grapes plus 5 lbs of blackberries

Each batch had the following ingredients added:
2 Tsp acid blend
2 Tsp yeast nutrient
1 Tsp pectic enzyme
2 tsp metabisulfite 
1/2 tsp grape tannin

9 to 10 lbs of sugar and water to bring the SG up to 1.085

The mixtures were allowed to ferment for 4 days in a primary container and then racked into the glass secondary containers … great aromas and rapid evolution of carbon dioxide. In the above picture at the back we have the purple grape juice, the green grape juice, the green grape skins plus blackberries and in the front the purple grape skins and blackberries.

To Filter or Not?

To date, with the few wine kits I have made, I have never filtered the wine before bottling.  Most of the wine kit instructions recommend filtering because it supposedly enhances the clarity of the wine, and removes some of the residual yeast cells that are still floating around.  With my valpolicella kit, the store gave me a coupon for a half day filter rental, so I decided to go ahead and try filtering this wine before bottling.  The store gave me a "Buon Vino Mini Jet" electric filter for the afternoon:  http://www.buonvino.com/minijet.html

The wine filter consisted of a pump connected to an arrangement of plates that force the wine to pass through a sequence of three filter pads, and then through an outlet to a long piece of tubing that carries the wine to a carboy for storage until bottling. The edges of the filter pads are exposed, which allows some wine to escape.  This is probably good for the pump, because if the filter pads get clogged, wine can escape through the sides, which prevents the pressure from building up.  Any overflow wine is collected in a drip tray which drains to a holding container via a length of tubing.

My valpolicella wine had been sitting for some time after clarification, and there was an inch of precipitate at the bottom of the carboy.  So, before starting, I racked the wine into a clean carboy.  This way, I didn't have to worry about the fine solids clogging up the filter pads.  I noticed that the racked wine was already pretty clear.

After the somewhat fussy process of sterilizing the pump and tubing, rinsing with cold water, and flushing water through the filter pads, I began filtering.  I was pleased with the filtration rate, which was a lot faster than what I usually get when I siphon wine from one container to another.  When the carboy of unfiltered wine was empty, I filtered the two litres of overflow wine.

The filtered wine was 'agitated'.  That is, there was a fine foam on the surface, which is meant to be the result of carbon dioxide out-gassing from all the mechanical agitation that happens during filtration.  It took a few hours for the foam to disappear.  As per the instructions, prior to bottling, I let the filtered wine stand overnight in a carboy fitted with an airlock.

Bottling was uneventful, and a sample of the wine tasted much like it did when I first tested it.

30 bottles of filtered Valpolicella

So, was filtration worth the effort?   Filtration seems like a really good way to degas the wine if there is any excess carbon dioxide or sulfur dioxide present.  It is probably a good way to remove any of the finings that are left in the wine after racking, but this only applies to instances of sloppy racking.  If you are careful with racking, your wine should be very clear and may not even need to be filtered.

I personally found it to be a fussy process that creates a number of opportunities to contaminate the wine (e.g. sterilizing and rinsing the wine filter is not easy because of all the little grooves and small parts).  Plus, the whole process is clearly a very good way to aerate the wine: the wine is squeezed through filter pads with high surface area (in air); the overflow wine sits in an open drip tray before flowing into an overflow container; the filtered wine flows at a high rate from the outlet tubing, and this created a sort of waterfall effect in the final carboy, mixing up the wine with lots of little air bubbles.  Basically, there was a lot of aeration.

Would I do this again?  On balance, probably not.

Apple Wine Racking & Tasting

It was just under three weeks ago that I racked the apple wine into a carboy where it could ferment to dryness.  At that time, I added three cinnamon sticks to add some flavour.  The bubble rate died off after a week, but there has been a low level of activity since then, with tiny bubbles forming on the surface.  This could be outgassing or maybe even the result of malo-lactic fermentation (MLF).  There is a lot of malic acid in apples, so MLF would not be surprising.  Today, I decided it was high time to rack it and perform a taste test.

I siphoned the wine into a clean carboy and added two crushed Campden tablets.  During the siphoning, I dispensed a small amount into a glass.  After stirring the wine to remove sulfur dioxide, measuring the specific gravity, and installing an air lock, I sat down with my notebook, pen, and glass of apple wine.

This is the best wine I have made to date.  The bouquet was of obviously of apple, but there was a hint of pear.  The taste was simply delicious and mild.  I was surprised at how much body it had, given that the ingredients were so simple.  There was hint of butter, which suggests that there may have been some MLF.  The cinnamon flavour was very mild, and in the background.  I only really noticed it at the end.  It confers a subtle amount of spicy 'heat' to the wine.  The acidity was just right.  I tasted it at room temperature, and I suspect it would be even nicer when chilled.

Tasting and the taking of notes.

For me, as a scientist and chemist, it is a joy to sit down with a new wine I have never tasted, and taste it carefully and slowly, with the intent to observe as much as I can.   A certain oenophile colleague of mine once pointed out how satisfying it is to try to describe what you see, smell, and taste.  Wine tasting is a lot more fun when you really slow down and pay attention to the complex mix of aromas and flavours that you experience in your nose and mouth.  A wine tasting wheel is a great help for this.

(As the wine isn't quite finished yet, this may be premature, but thanks to +Bob Perkins and +Pete Bottiglier for some of the tips you shared that I followed with this apple wine.  To your health!)
  

The Limitations of EZ Cap Bottles

For about two weeks now, my cider has been sitting in those cool looking EZ Cap bottles.  Two days after bottling the first batch, I noticed tiny bubbles rising to the top, inside the bottles.  I thought this was a good sign, as it meant that the secondary fermentation was working, and the cider should be nice and carbonated when it was all over.  The problem is that the bubbles have not stopped.  That can only mean one thing:  the EZ Cap bottles leak.

Bubbles can only form if there is somewhere for the gas to go.  If the bottle is under sufficient pressure, the CO₂ stays dissolved in the liquid, and there are no bubbles.  However, as soon as the pressure drops, CO₂ becomes gas, and bubbles become visible.  This is exactly like opening a pop bottle.  When you unscrew the lid, the pressure inside the bottle drops, and CO₂ is released.

In exactly half of my 1 litre EZ Cap bottles, tiny bubbles are still forming in the cider.  Last night, I decided to open one of the leaky bottles and test it.  When I popped open the lid, there actually was an audible pop as if the bottle was under a small amount of pressure.  When I poured a glass, however, the cider was clearly not carbonated.  (So, I added some club soda and proceeded to enjoy!)

I really like EZ Cap bottles.  They look nice and they are easy to use.  I think they are perfect if your goal is to make still cider (i.e. non carbonated).  But if you want carbonated cider, you will need to use beer bottles and bottle caps, or maybe a plastic pop bottle with a tightly screwed lid.  Now, my experience might not be a total failure.  I still have hope for the other bottles of cider that don't have bubbles, because that suggests they are under pressure.  But here's the thing - a 50% success rate of getting a strong seal just isn't good enough for this purpose.

Here's my question:  Is there a trick to getting a good seal on EZ Cap bottles?

Bottling Cider

Yesterday, once I concluded that the fermentation was complete, I racked apple cider v.1 into a clean 1 gallon jug.  A secondary fermentation is required to carbonate the cider, so I stirred in some extra sugar - recipes often call for 1/4 cup of sugar per gallon.  I added a little less than this and stirred it until it was dissolved.  Then, I siphoned the cider into three 1 Litre EZ-Cap bottles.  The plan is to wait 2-3 months before I crack open a bottle.  This should be plenty of time for the secondary fermentation to be complete, and the lees to mostly settle out.

EZ-Cap Bottles.  Don't they look good?

Apple Cider, Apple Wine

As I write this, the room is nice and aromatic, full of the smell of apple.  It seems to me that fermentation enhances the richness of fruit aromas.  It's fantastic.

Here's what I did with all that pressed apple juice.

Apple Cider v.1

This cider is made from the apples from our own small apple tree in the back yard.  It is a Norkent variety that is hardy in our northerly climate.  The yield of apples was modest, and we only obtained about 1 gallon of juice.  I added one crushed Campden tablet to the juice.  Specific gravity of the juice was 1.035, so I added 1.5 cups of sugar, bringing s.g. to 1.050.

Once transferred to a 1 gallon jug, I added 1/4 tsp. of peptic enzyme and 1/4 tsp. of yeast nutrient, stirred.  I was perhaps a little bit too eager and went ahead and sprinkled about 1/3 of a packet of sparkling wine yeast on the surface.  From various recipes and instructions, it seems that peptic enzyme may work better prior to adding yeast and starting fermentation, but I don't see any scientific reason for why that would be the case.  Anyway, I went ahead and added the yeast and placed an airlock on the jug and waited for the magic to happen.

Cider fermentation

Apple Cider v.2

All the other apples that we obtained from generous friends produced in total about 4.5 gallons of juice.  This time, I more or less followed the instructions in the Winemaker's Recipe Handbook (the "purple book").

I added 4 Campden tablets, 1 tsp. of peptic enzyme, and 2 tsp. of yeast nutrient.  The specific gravity for this apple juice was the same as the first batch (1.035).  I added enough sugar to bring the density to 1.055.  I let the juice sit for 24 hours before transferring 3 gallons to a carboy and adding the yeast.


Apple Wine

There was a lot of leftover apple juice from the above cider batch, so I improvised a batch of apple wine.  I diluted the juice to just over 3 gallons, added sugar until the specific gravity was 1.090, and then added a packet of sparkling wine yeast.  That's all.  This batch is currently fermenting away in a plastic bucket with a loose fitting lid.

My plan is to add some spices to the wine when I transfer it to the secondary.  (Does anyone have suggestions on what to add?)

How do you like them apples?

Today, the aromas in my home office/fermentation room are lovely.  There are three separate fermenters in action: two with apple cider and one with an apple wine.  The air is filled with methyl butanoate (the main ester compound that contributes to the smell of apples) and a number of other minor compounds that contribute to the fruity atmosphere.  If I keep the door closed, the aromas build up and become a bit of a distraction.

A couple of days ago, I decided to go ahead and try making apple cider and maybe also apple wine if I had enough apples.  Our own apple tree is still small, and our harvest consisted of a single cardboard box full of apples.  My wife sent out an A.P.B. to her friends to see if anyone had apples they wanted to dispose of, and we quickly obtained an additional 4 cardboard boxes full of apples.

I rented a fruit crusher and press from my favourite store, Wine Kitz - St. Albert, and got to work producing fresh apple juice on our patio.  This was by far the most fun I have had in making fermented beverages. 

The fruit crusher (see picture) consists of a rotating shaft with sharp blades that chop up the fruit into smaller pieces.  Chunks of fruit are drawn into the space between two rotating metal rollers that crush the fruit.  The crushed fruit and juices can be collected in a bucket placed below the device.  Initially, we used a plastic pail to collect the mashed apples, but then switched to a large blue recycling box lined with a garbage bag.

The Crusher: put apples in the hopper and turn the wheel

We dumped the crushed apples into the wine press.  The wine press was fun to use.  Two thick semicircular wooden discs go on top of the fruit, and then you put enough wooden blocks on top of the discs to reach the ratchet plate.  You screw the ratchet plate down by hand until it is sitting on the blocks, and start applying real pressure by cranking down the ratchet plate using a metal lever.  The juice gets squeezed out the sides of the basket and into a collecting tray with a spout.  We collected the juice in a large plastic pail.

My wife and I taking turns using the press.

Under pressure, the juice flows quickly.  Of course, we tasted it.  It was the sweetest, yummiest apple juice I have ever tasted.  In fact, it was so much better than store-bought apple juice that it really makes you wonder why.  The kids loved it too, but I wouldn't let them have much.  It is immensely satisfying to hand-pick several boxes of apples and then use your own muscle power to squeeze out 5 gallons of delectable apple juice.

The products of pressing:  apple juice and pomace.

(This post is getting a bit long, so I'm going to write about the apple cider and wine separately.)

Valpolicella Racking, Stabilizing, and Degassing

Today, I racked, stabilized, and degassed the Valpolicella wine.  The kit instructions are to do this at day 14, but this is day 19.  I let the wine sit an extra five days because the fermentation was not quite complete at day 14.


After the usual sterilization of equipment, I transferred the wine to a clean carboy via autosiphon, without incident.  During this 'racking' step, I took a sample for a tasting.  Well, well, this is nice stuff.  This wine is dry and gentle.  There are woody and nutty tones with a hint of almond.  The tannins are noticeable at the end.  I have hopes for a very nice table wine that will pair well with pasta dishes.

Tasting.  Note-taking is important when it comes to stuff like this.

The specific gravity was 0.990.  From the starting point, this gives approximately 16% alcohol.  Yes, it's pretty dry.


The next step is the addition of potassium metabisulfite, which is provided with the kit.  Out of curiosity, I used my little portable balance to measure the mass of K₂S₂O₅.  The mass of K₂S₂O₅ was 4.4 g.  For comparison, I weighed a Campden tablet.  It was 0.6 g.  The recommended use of Campden tablets is 1 tablet per gallon of wine.  This is a 23 L kit, which is about 6 gallons.  6 gallons x 0.6 g per gallon = 3.6 g worth of Campden tablets.  So, this amount isn't too far off.

When you add the K₂S₂O₅ to the wine, SO₂ gas is formed (see picture).    The chemistry of this step is quite straightforward, and one of these days I'm going to write a blog post about it.

SO₂ bubbles.  You can get rid of the excess gas by stirring vigorously.

After the K₂S₂O₅, I added potassium sorbate and then a small packet of kieselsohl.  Tomorrow, I complete the addition of clarification agents, and then I wait three weeks until bottling.

Valpolicella Wine Kit

A couple of months ago, I bought a wine kit that was on sale:  Wine Kitz Traditional Vintage Valpolicella.  It is meant to be a nice table wine.  This last weekend, I finally got around to starting it.  The kit consisted of 10 L of concentrated valpolicella grape juice and packets of yeast, potassium metabisulfite, potassium sorbate, kieselsohl, and chitosan - all the consumable materials you need.

Naturally, you start by sterilizing all of your equipment.  Then, you simply mix the grape juice with enough water to give you 23 L and sprinkle the yeast packet on the surface.  The fermentation starts up quickly -  more or less as soon as any dissolved oxygen is used up by the yeast.

10 L bag of valpolicella grape juice

The fermentation is now in progress inside a large plastic bucket.  The bucket has a loosely fitting lid which allows the carbon dioxide gas to bleed out.  Because of this small amount of gas escaping, the room has a background of fruity/bakery sorts of aromas.  The home office always smells nice when something is fermenting.

A little peek under the lid to see the primary fermentation (day 3).

Rhubarb Wine - The Final Result

I bottled the batch of rhubarb wine about 10 days ago.  The clarification step and the bottling were completed without incident. 

Since bottling, I had the pleasure of serving the rhubarb wine to visitors.  They seemed to enjoy it.  Not only did they finish their glasses, but they filled them up for a second round.  I think that qualifies as a success, especially considering the wine's undrinkable state after fermentation.

Chilled rhubarb wine on the deck.  It's perfect for
a hot summer afternoon on the Canadian prairies.

If I could compare this wine to anything, it would be cider.  The wine has good legs, there is a bit of tartness, but it's easy to drink.  The rhubarb flavour is mild and pleasant.  Have it with a slice of apple pie and ice cream and you know you are living the good life.

Cheers!

Sweetening the Rhubarb Wine

 A few days ago, I picked up two bottles of Sweet Reserve from +Jim Miller at the St. Albert Wine Kitz store.  He also offered some thoughts about rhubarb wine and it's extreme acidity.  I learned that it can be advisable to add chalk to the must, just to neutralize the acid.  (Now, why have I never seen that in any posted recipes for rhubarb wine?)

Sweetening the rhubarb wine.  Carboy, bottle of sweet reserve,
wine glasses with different amounts of reserve (sweeter from
left to right), measuring spoon, and notebook)

This morning, I got to work on sweetening my rhubarb wine, which was too dry and acidic to enjoy.  Using a wine thief, I removed approximately 250 mL of wine and placed it in a measuring bowl.  Then I poured out 1/4 cup (62.5 mL) into each of four wine glasses.  Using a 1/2 tsp (2.5mL) measuring spoon, I added different amounts of sweet reserve to each glass, stirred each, and then tasted them all.  Here are the results:

 

Glass #2 was the winner.  The addition of 5 mL per 62.5 mL of wine is a 0.08 added volume equivalent.  Using some algebra, I determined that I needed to remove 840 mL of wine from the full carboy, and replace it with an 840 mL of sweet reserve.  This step went smoothly.  I stirred up the new mixture with my plastic mixing 'stick', and sealed the carboy with an air lock.  My plan is to let it sit for a few days just to make sure it's stable, and then I will clarify it.

Just for fun, after sweetening, the specific gravity was 1.010.  (I haven't worked it the exact amount yet, but this was a LOT of added sugar.)

Happy Canada Day!

Homemade Labels

However much I like the peel and stick labels you can get for wine kits, it's much more fun to make your own.  I like to employ children to help with this.  They love it.

First, ask the young person to draw something related to the type of beverage.  When they finish, scan the image and then make up your label in Powerpoint by inserting the image and adding text.  Resize the label and print!

To stick the label on the bottle, I simply use glue stick.  It keeps the label on just fine.  When you are finished with the bottle's contents, it's very easy to wash the label off because glue stick is more or less water soluble.

It's that easy.  Take a look at the mead that was bottled a few days ago.  The label adds a sort of professional touch.  (Also, notice how clear the liquid looks.  The fine solids have settled out!)

Sunnyside Mead 2014

It's a Learning Curve

For a number of reasons, I waited until today to rack and stabilize the rhubarb wine.  This was partly due to just being busy, and partly a conscious decision to let this fermentation go to virtually 100% completion.  This afternoon, the bubble rate was about one every four minutes.  If that's any indication, then this fermentation was awfully close to being 100% complete.

The racking went smoothly.  I took a specific gravity reading (0.990), which would correspond to 16.3% alcohol.  Hmmm.  This is pretty strong stuff!  I also took a small amount in a glass for tasting...

Oh dear.  It's rhubarb mouthwash.  The last time I tasted the wine, at the first racking, there was still some sugar present, and it was delicious.  The acidity of the rhubarb and the residual sugars balanced each other and gave some nice flavours.  At this point, all the sugar is gone.  There is no more sweet!  It's just pure acidity.  This is a dry, acidic wine, probably only good for marinating fish or something like that.

So, what would I do differently next time?  In hindsight, I should have stopped the fermentation and stabilized it a few days after the first racking, when there would have been some sugar left to balance all the acid from the rhubarb.

In any case, I went ahead and stablized the wine.  When I added the potassium metabisulfite, I noticed a colour change.  This compound certainly appears to be causing a bleaching of the colour (see below).  It remains to be seen whether this is reversible, like it was the first time:  http://randomfermentations.blogspot.ca/2014/05/rhubarb-wine-beginning.html

(1) Rhubarb wine after racking and addition of a small amount of postassium metabisulfite (left).  The photo on the right was taken about 1 minute after the first one.  Notice the colour change.

This really is a bit of a bummer.  I put a lot of work went into making this rhubarb mouthwash!  On the other hand, I learned a good lesson:  Listen to what your taste buds tell you!  If the alcohol level is close to where it should be, and it tastes good, then it's time to rack and stabilize.

Just like many things in life, there is a learning curve to this.  It's important to continue and try to get it right the next time.  My rhubarb plant has grown back (it's gigantic), so I have the materials to start again.  Next time, I'm going to listen to my taste buds.

Bottling the Mead

Mead v.1 was ready for bottling about a week ago, but I could not find time to bottle it.  May and June are always a crazy time at universities, so there have been a lot of demands at work.  Also, we've been working on a deck at home, which has used a lot of time on the weekends.

This morning, I had waited long enough and decided to go for it.  First, I siphoned the mead from its 3 gallon carboy into another one. Why did I do this?  There is a fine precipitate sitting at the bottom of the carboy  the result of clarifying the liquid.  It is easily disturbed, and during the bottling step, there can be a lot of movement of the siphon tube.  By transferring the liquid to a separate container first, it is easier to avoid disturbing those fine solids.  It has certainly worked out well in the past.  But this time, I managed to slightly disturb that precipitate and some of it got into the liquid.  It wasn't much, but there was a slight turbidity to the mead that I ended up bottling.  This is frustrating because the liquid was crystal clear before, and it was an avoidable mistake.  I just hope it settles out over time.

I used my auto-siphon to fill the sanitized bottles (pictured below).  The end result was fourteen 750-mL bottles of mead!  There was little extra, so I put it in a separate bottle and placed it in the fridge.  (This was so I could see what it tastes like when chilled.)

(1)  Bottling.  I don't really need to wear rubber gloves 

for this, but I was sanitizing with bleach solutions, and it was 

easier to just leave them on!

Several hours later, I am writing this with a small glass of chilled mead at hand.  First of all, this stuff is strong - certainly stronger than most wines.  You may recall that I estimated the alcohol content to be 15% or so.  It is obviously sweet, with a mild honey taste, and a hint of oak and cedar.  There is almost no acidity, and the finish is surprisingly clean.  And, yes, it is better served chilled, just like most dessert wines. 

When my wife tried it, she immediately looked up at me with her eyes wide, and said, "Yummy!"  This brings me to an important observation: this mead is ready to drink.  One doesn't need to age it for months and months before uncorking a bottle and pouring a glass.

My daughter asked if she could help make labels.  She drew a nice picture of a commercial bee hive.  From her artwork, I thought the name "Sunnyside" was appropriate.

(2)  Homemade bottle label.

Yesterday was summer solstice in the northern hemisphere.  If only I had bottled this a day before, I could have celebrated the longest day like the ancients - with a glass of mead!

Rhubarb Wine: Interim Satisfaction

Twelve days ago, I started the rhubarb wine.  I've been out of town for half of that time.  Today, I got around to checking on the progress.  When I opened the lid on the plastic bucket and looked at the surface, I could tell that fermentation was on the tail end.  There just wasn't a lot of "activity" in terms of bubbles.  I quickly sterilized a 3 gallon carboy and my auto-siphon and got to work racking the wine into a carboy.

Some observations:

1. Specific gravity = 1.012.  The initial s.g. was 1.097.  Therefore, the approximate alcohol content at this point is somewhere between 13.0 and 13.5 %.  (It's getting close to being done!)
2. The colour!  There is a nice peachy pink colour now.  I thought the colour had been totally  bleached by the campden tablets, but there might be something else going on.
3. The taste!  (Naturally, I tested it!)  There was no tartness at all, just a mild rhubarb flavour, along with a gentle grape taste from the concentrate that I added.  This has the potential to be a very nice dessert wine.

Front: Rhubarb wine, with some colour.  

Back: Mead, just prior to adding kieselsohl.

Mead v.1 has been sitting in a carboy for about 12 days as well, and there was a nice build up of lees at the bottom.  I racked it into another carboy and then added the kieselsol, which is step 1 of the finings.  And, I sampled the mead too.  It's getting better!  The taste has mellowed out a little and I think it will be really nice when it is chilled.

Rhubarb Wine - An Inauspicious Beginning

The forced rhubarb thing actually works! As you can see in the picture below, the stalks are pale looking, and the leaves have very little green pigment. The forced rhubarb stalks themselves are very tender, and have none of that celery-like fiber that makes rhubarb so tough.  This is all good, but my  forced rhubarb was not a 100% success.  In places where the rhubarb had received a bit of light before I covered them up, or from imperfectly dark conditions, the rhubarb grew to an intermediate state.  It wasn't quite like the forced rhubarb in the picture below, but it wasn't like normal rhubarb either.

 

(1) Me and my forced rhubarb.

So, having collected all the rhubarb I could, I chopped it all into thin slices.  The result was 17 cups of chopped rhubarb.  I placed it in a big white plastic bucket and added 6 L of water and two crushed Campden tablets.  The Campden tablets are added to keep the bacteria at bay.

(2) Chopped rhubarb in water.

The next morning, I scurried off to the store to get some pectic enzyme.  Pectin is a carbohydrate in cell walls.  Pectic enzyme helps break it down and that, in turn, releases more of the sugars and flavors.  When I returned, and opened the lid on the bucket, I was very surprised.  Overnight, the red colour of the rhubarb had been bleached!

This was initially a mystery to me.  The bucket was rinsed well before use (i.e. perish the thought that there was any bleach leftover from sterilizing).  Campden tablets, however, contain potassium metabisulfite, which is a reducing bleach - something I just learned.  That means it bleaches colours by removing oxygen as opposed to adding oxygen (which is how household bleach and peroxide work).  So, for now, I'm going with the idea that the culprit was the small amount of metabisulfite in the Campden tablets.  It's going to be a "white rhubarb" wine.  At least it still smells like rhubarb!

(3) Bleached rhubarb

I added 1/2 tsp. of pectic enzyme and stirred the mixture occasionally for the next 36 hours.  At 48 hours, I removed the rhubarb from the water by straining.  Then, I added 1 L of white grape juice concentrate, and 14 cups of white sugar.  This was not some magic recipe: I simply kept adding sugar cup by cup until the specific gravity was between 1.095 and 1.100.  The final value was 1.097.

I added 3 tsp. of yeast nutrient and a packet of activated yeast.  And then I went to bed.  The fermentation is now underway in the bucket.  It smells good!

Mead at 6 weeks

For the last two weeks, the fermentation rate has been falling slowly.  Two days ago, I made the decision to stop the fermentation.  There was a nice layer of lees at the bottom of the carboy.  The bubble rate was down to 2 per minute.  I reckon that the fermentation probably would have continued for a week longer.  It was the specific gravity that tilted the decision to stop.  The initial specific gravity was 1.120, and it had fallen to 1.019.  Yes, with that final specific gravity, there is probably a small amount of fermentable sugars remaining.  However, from the hydrometer scale, the difference between starting and final specific gravities corresponds to an alcohol content of approximately 15%.  I felt that this was more than strong enough.  If there's a little sugar left, so be it.  It will taste sweeter.

So, I siphoned the mead into a sterilized secondary fermenter, and then added 1 tsp. of potassium metabisulfite and 3/4 tsp. of potassium sorbate, with lots of stirring in between.  Two days later, I haven't noticed any activity, and there is a nice layer of lees that has already settled out.

(1) Mead immediately after racking to the secondary.

After racking the mead, there was a small volume remaining in the primary and in the siphon hose.  So, I sampled it.  It was better than the junk I was served at that barbecue many years ago.  However, the unprocessed mead I tasted had some carbon dioxide in it, which made the taste sharp.  That will hopefully disappear with time.

 (2) Sediment two days after racking.

My plan is to let this sit for the next week or so, and then add the finings to make this beverage crystal clear, and ready for bottling!