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.

Dragon Blood Trial & Error

Back on May 21, I racked my first batch of Dragon Blood and did a taste test.  My notes say everything that needs to be said:

"Taste Test:
Dry, slightly acidic, and the taste was like diesel.  There is something in it that doesn't taste right.  Perhaps one of the fruit components like pomegranate or cherry?"

It is early, and the taste may evolve over time.  However, I am now a little cautious about experimenting with out-of-the-ordinary frozen fruit mixes such as the one I used on this particular batch.  Dragon Blood is usually made with common triple berry mixes (blueberry, blackberry, raspberry).

With that cautionary lesson, I went ahead and purchased a frozen triple berry mix and used the same basic recipe as the previous batch:

Dragon Blood v.2

3 gallons distilled water
17 cups granulated sugar
1 tsp peptic enzyme
2 tsp yeast nutrient
1.5 tsp acid blend (tartaric, citric, malic acids)
3 campden tablets (crushed)
2 kg of "Triple Berry Blend", in a nylon mesh bag (tied-off)

(The only differences are in the slightly higher amount of sugar required to get to the same starting s.g., and the larger mass of berries - which is simply because that was the amount in the bag!)

I started this one week ago.  The starting specific gravity was 1.087.  It is now 1.048.  I'm going to wait a couple of days, check the s.g., and rack to a carboy.

"Dragon Blood"

One of the best things I have done related to wine making is to join the Home Made Wine Making Google+ Community.  Community members are always posting interesting things and there is a lot of recipe sharing that goes on.  One of the wine recipes that frequently pops up is known as "Dragon Blood" - a name that was coined by a home made winemaker known as DangerDave.  DangerDave's Dragon Blood recipe is a variation of berry wine recipes that are described, for example, in that little purple "Winemaker's Recipe Handbook".  DangerDave's innovation is to use a frozen triple berry mix, found in the frozen food section of just about every supermarket, as the fruit.  By all accounts, Dragon Blood is easy to make and it can be ready to drink in less than two weeks.  This seemed like something worth trying.

As it happened, one day I was shopping at Costco, and spotted a frozen organic fruit mix (blackberry, blueberry, cherry, pomegranate, and strawberry).  This was just the thing to use in a first attempt of a Dragon Blood variation.  This frozen fruit sat in my deep freeze for a few months and I recently decided to get on with it.

"Super Fruit Blend"

As it is with chemistry experiments, so it is with wine making: The first thing you do is spend some time planning what you will do.  In wine making, this means reading and comparing different recipes, and then coming up with your own.  On looking at DangerDave's recipe, I was little nervous about how much lemon juice (48 oz.!!) is added because that is just too much acidity for me.  My purple handbook has a number of berry wine recipes that include only small amounts of acid blend, to improve the balance.  I decided to opt for that approach rather than load it up with lemon juice.

Here's the recipe:

3 gallons distilled water
15 cups granulated sugar
1 tsp peptic enzyme
2 tsp yeast nutrient
1.5 tsp acid blend (tartaric, citric, malic acids)
3 campden tablets (crushed)
1.5 kg of "Super Fruit Blend", in a nylon mesh bag (tied-off)

The sugar, peptic enzyme, yeast nutrient, acid blend, and campden tablets were dissolved in 3 gallons of water, in the primary fermenter (white plastic bucket with lid).  The frozen fruit, in a tied-off nylon mesh bag was steeped in the mixture for the next 24 hours.  During that period, I wrung out the bag a few times to squeeze out the juices and infuse the fruit with peptic enzyme.

Fruit in nylon mesh bag.

Ready to steep.

After steeping, and prior to adding the yeast, I took a density measurement so I could estimate alcohol content later.  Specific gravity = 1.087.  I added the yeast (1 packet of sparkling wine yeast) to get the fermentation started.

Primary fermentation underway.

During the primary fermentation, there were nice, mild, fruity aromas in the room.  Every other day, I stirred the mixture to help draw out the fruit flavours.  By the sixth day, the specific gravity was 1.035.  This was low enough that I siphoned the must into a carboy for secondary fermentation.

Secondary fermentation (4 days after transfer)

So there it is.  Fermentation is still going.  My plan is to let it go right to dryness before bottling.

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.