Pomace wine

Making wine from fruit is very easy, usually much easier than making alcohol from grain.  In a previous post about yeast  it is proposed that early man discovered by almost unavoidable circumstance how to make this alcoholic beverage.  Although the basic process of winemaking is simple, making a consistent product from batch to batch or from year to year is more difficult and requires some science.  The physiological ripeness of grapes or other fruit, the effect of differing yeast strains and the development of tannins as wine ages can become complex subjects indeed.  This post attempts to brush by the more subtle aspects of winemaking, but still show the uninitiated novice that making a good wine can be a simple and rewarding task.  What will be referred to here as a “pomace wine” process seems to work well for white wine grapes and other fruit like peaches, plumbs and apricots.

“Must” is freshly pressed fruit juice which contains particles of skins, pulp, seeds and stems.  These solids in must are referred to as ‘pomace’.  The length of time that the winemaker might allow pomace to remain combined in the must can have a large influence in the final character of a wine.   The pigment and tannin content of a wine will be increased if the pomace is allowed to remain throughout primary fermentation.

This alternative pomace process differs from the more common practice of just squeezing and separating the juice from the pulp before beginning fermentation.   While grapes are used in this example, the method is probably even more applicable to wines made from most any other type of fruit.  The advantages of this pomace wine method might become self evident in terms of labor efficiency, by more desirable color and flavor in the final product and by the conversion of more sugars into alcohol.

After fermentation the wine is normally separated from the pomace by “racking” or siphoning only the clear wine from one container to another.  The solids are usually just tossed away, which is a waste.  That pomace (the solids) in the wine might represent a significant mass in its own right and can still be exploited further because it holds useful amounts of yeasts, nutrients and ethanol.   The yeast could be recovered, washed and preserved by a method called “cold crashing”.  The leftover pomace would also still be rich in ethanol.  Water might be added to this residual pomace to make a second, perhaps thinner batch of wine or these wet solids might be distilled to create a “poor man’s pomace brandy” like Grappa.  If that distillation is added back to the clarified wine then a “fortified wine” (like Sherry, Port or Madeira) is created.

Grapes are easy

Yeasts thrive in a slightly acidic environment.  For wine the ideal acidity is about 0.6% which is roughly equivalent to pH 3.5.   Grapes generally come with close to ideal acidity for purposes of winemaking.  There are thousands of varieties of grapes and most will range between pH 2.80 to pH 3.84.   Fruits in general tend to be more acidic than vegetables.  Less acidic fruits like bananas and coconuts however would need to be amended with a little tartaric or citric acid prior to fermentation.  Acidity also comes into play later during the clarification of a wine.  Cloudiness in a wine is the result of suspended, electrically charged proteins & polyphenols.   To clear haziness in a wine, periodic racking, filtration and ‘fining’ or ‘clarifying agents’ can be employed.   This potentially complicated topic will be approached a little later.

Aside from having a low pH, grapes have a high monosaccharide sugar concentration.  Grapes have an abundance of easily accessible glucose & fructose which allow the ‘sugar loving yeast’ Saccharomyces cerevisiae to quickly flourish and perform its magic.  By contrast a grain wort has complex sugars or starches which require a “cracking” into monosaccharide form, before production of ethanol can commence.

1 Wash

In the above photograph the grape clusters are dunked in a mild Clorox (bleach / calcium hypochlorite) bath, next in a disinfecting sodium bisulfite solution and finally a rinse of pure water.  This process rids the grape clusters from most insects, arachnids, bacteria and wild yeast.   Finally the grapes were separated from the stems.

2 Process

Next the grapes were juiced in a food processor.   Some sources will discourage the thought of processing grapes in a blender, for fear of releasing undesirable tannins from crushed stems and seeds.  In this case however the stems were tediously removed beforehand and there is actually little probability of cracking individual seeds when the blending is done briefly and cautiously – just enough to liquefy the pulp.  Carefully controlled pressure would need to be applied in a commercial wine presses also – to avoid crushing the seeds.

Some winemakers might pour the must into a bag of cheesecloth to facilitate the easy removal of the pomace later.  Here though, the juiced pulp was simply poured into a sterilized fermentation bucket.  After the fermentation bucket was almost full then ¼ teaspoon of sulfur dioxide was mixed into the pulp and the lidded and rag covered fermentation carboy left to sit for 24 hours.  This kills remaining bacteria and wild yeast, some of which reside naturally inside the fruit.  It is important not to completely fill the fermentation bucket.   Leave an airspace of 2 or 3 inches at the top to reduce the possibility of an overflow during fermentation.   Also fermentation buckets like this have 6 U.S. gallons capacity; the excess volume is usually needed to fill a 5 gal glass carboy after a racking or transfer that leaves unclear sediments behind.

3 Oxygenate 

After the 24 hour waiting period the sulfur dioxide will have dissipated, being consumed by killing bacteria, trapping oxygen and reacting with aldehydes.   In the picture above the must has separated into sugar rich juice at the bottom and lighter pomace at the top.

4 Inoculation

Almost any type of yeast can be used but the choice will dictate the flavor profile of the wine.   Here a Canadian yeast known as ‘Lalvin  71B-1122’ was used although there are several other fine brands of commercial wine yeast to choose from.  While a Champagne yeast would produce more alcohol, this strain was picked because of its lower alcohol tolerance (about 14%).  By not consuming all the sugar from the grapes this yeast is expected to create a less dry and softer wine and to preserve or enhance the fruit flavor and add fruity esters.

Normally one could just sprinkle the yeast package over the must and stir it in, where with luck wine will be produced in about a week.  In this case however a yeast starter was created and used.   Creating a so-called ‘yeast starter’ is simply a means of ‘proving the yeast’ and of insuring a vigorous fermentation.   A couple of cups of juice were scooped out and the yeast added to that.  In a glass quart jar covered with a paper towel to allow oxygen to pass but protect against the introduction of airborne bacteria and wild yeast, with sugars to feed on the number of yeast in the starter can be expected to double every 3 hours.  With the yeast, 3 tsp. nutrient and 2.5 tsp. pectic enzyme were added to the starter solution at the same time in this instance.

* Pectic enzyme or pectinase breaks down the complex and stubborn polysaccharides (long chained sugars) found in pulp and skins. Pectic enzymes can also improve fining and filtering operations of high-pectin wines.

* Pectin is the jelly-like matrix which helps cement plant cells together.  It is a structural polysaccharide contained in the primary cell walls of plants.  Fruit ripens and becomes softer as the enzymes pectinase and pectinesterase break pectin down.  Pectin acts as a soluble dietary fiber which traps carbohydrates and binds to cholesterol in the gastrointestinal tract. Pectin separated and concentrated from citrus fruit is used as a gelling agent in jams and jellies.

* Yeast nutrient provides the vitamins, amino acids, nitrogen, potassium and phosphorus that yeast cells need to grow well.   Contents of packages labeled “Yeast Nutrient” may include: dead yeast, folic acid, niacin, diammonium phosphate, calcium pantothenate, magnesium sulphate and thiamine hydrochloride.   Homemade nutrient might be made from ammonium or potassium sulphate and ammonium or potassium phosphate plus a few vitamin B1 pills.   Plain un-sulfured molasses is full of vitamins and minerals.  In laboratories a drop of molasses water is commonly added to cultures in Petri- dishes; to stimulate yeast growth and reproduction.

While sodium bisulfite powder was used both as a sterilizing agent and as source of sulfur dioxide for wine in this instance,  Campden tablets are perhaps more popular.  Potassium or sodium metabisulfite Campden tablets are also used as an anti-oxidizing agent or to remove chlorine from water.  What Canpden tablets can and can’t do…

By no means is it necessary for a winemaking novice to purchase or use a hydrometer.   The use of one though offers the brewer a little more understanding and control over the process of fermentation.   Hydrometers measure the specific gravity of liquids and different versions can be found to measure the amount of cream in milk, sugar in water, alcohol in liquor, water in urine, antifreeze in car coolant or sulfuric acid in a car battery.  Simply put for winemaking purposes here:  water containing sugar is denser than pure water and pure water is denser than ethanol. In the picture above: pure water in the beaker should read 1.000 but the fresh grape juice in the image reads a denser specific gravity of about 1.070.   This reading indicates a potential alcohol by volume (ABV) between 9 and 10% once the sugars are consumed by fermentation.  As fermentation commences the hydrometer will appear to sink in each sample, eventually reading less than the density of pure water.

5 Fermentation

Yeast cells reproduce in an aerobic (with oxygen) environment but create ethanol in an anaerobic (without oxygen) environment.   In this instance the fermentation bucket was lidded but allowed to breathe for another 24 hours before an S-shaped bubble airlock was fitted to the bung-hole.   Within 5-7 days about 70% or ¾ of the fermentation should be accomplished.   At this point (or when the specific gravity reads between 0.990 and 0.998) the young wine should be transferred to another container, leaving the pomace and sediments behind.   Either fresh water or additional fruit juice (if extra was acquired and refrigerated) should probably be added to the secondary container fill it.  This step is intended to reduce oxidization by limiting the amount of oxygen in contact with the wine.   Adding water to wine weakens it however while adding new juice might require the addition of more sulfides (which would stun the yeast).  The wine should be allowed to rest in the secondary for another 4 to 6 weeks or until it becomes clear.  At this point the wine can be bottled.

Advanced topics

Sulfides are added to wine at the time of bottling to keep it from spoiling or turning to vinegar later.   You don’t want to add too much sulfide to your wine however because it has an obvious smell and taste.  Some people have allergic reactions to sulfides but in general, health concerns regarding sulfide levels in wine are undecided.  The following link discusses how to accurately judge the proper sulfide level.  “ Should I add Campden tablets each time I rack my wine and how do I measure the level of sulfite in my wine? “

This link can be ignored by the winemaking beginner but it is a good source of information.  The root url (winemaking.jackkeller.net) leads to a fairly through homepage dedicated to winemaking.   Winemaking Additives and Cleansers

White wines will generally clarify sooner than red wines.  Racking is the preferred method for clarifying wine but when haziness in the wine persist ‘fining’ or ‘clarifying agents’ can be employed.   Sparkalloid, Isinglas, egg albumen and gelatin are examples of positively charged finings whereas Bentonite and Kieselsol are negatively charged.   This link  provides more information about fining agents.

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In conclusion, making wine with the pomace rather than without it is an alternative method which can offer several advantages.   Firstly this method does not require a grape press or an antique food mill or grinder.  This process also offers options for modifying a wine’s flavor and color profile which would not be available by the press method.   The pomace once separated from the wine can be re-hydrated to make a second wine or the intrepid individual might choose to produce a fortified wine or pomace brandy by utilizing these normally discarded solids.