Prepping for Bottling

It is good to be back in the blogging saddle again after a frenetic harvest and a wonderful Thanksgiving. I trust all of you had a wonderful holiday weekend with wonderful food, family and of course wine.

Alas, all good things need to come to an end and it was with a sad heart and a few extra pounds that I am prepping our wines for our bottling, due to take place this coming Monday and Tuesday. We have decided to put some of our tank fermented wines in the bottle, feeling that they are market ready, even though they were grapes on the vine 10 weeks ago.

We are bottling a new wine called V2 [a blend of Verdejo and Viognier], our ever popular LVD Viognier and a Rose’ made entirely from Touriga Nacioanale. All these wines are showing beautifully and we at Keswick Vineyards are incredibly proud of them.

The cellar is chock-a-block full of corks, capsules and bottles, with final lab tests being run to ensure the integrity and stability of the wines before we put them in bottle.

Prior to bottling though, there is a lot of work that goes into preparing these wines for this process, for we have to ensure the wine is both protein and cold stable, and devoid of any harmful bacteria or yeast that can contaminate the wine while in the bottle. After which the wines are filtered to ensure that all yeast and bacteria are removed from the wine.

Protein Stabilization

The grape berry contains a large variety of nitrogen compounds, mainly amino acids, peptides (short amino acid chains) and proteins (long amino acid chains). They serve various biological functions within the grape such as enzymes, cell wall components, etc. Amino acids are soluble, and wine yeast can use them to grow and ferment the grape’s sugars into alcohol. Amino acids, together with ammonium ions, are referred to as yeast available nitrogen (YAN). Peptides and proteins are not considered (YAN) because they cannot be metabolized by yeast. Their solubility decreases with the wine’s alcohol content. This may lead to precipitation of proteins in the form of a visible haze. This effect is accelerated or triggered by exposure to elevated temperatures, e.g., when a customer buys a bottle of wine in the tasting room and leaves it in the car over the weekend. Protein haze cannot be tasted; they are a purely aesthetic, visual problem in wine. I would imagine most customers would expect the wine to be clear, unless drinking wine that has the look of dirty water seems like an appealing notion.

The way in which take care of this issue is by adding CLAY, no you did not hear incorrectly CLAY. Pretty cool right. The clay in question is Bentonite, calcium based that when added to wine adsorbs proteins and renders the wine protein stable. Before we add this we do plenty of bench trials since we do not want to add to much as they can strip some of the desirable aromatic components in the wine, and in the case of our Rose, could also lead to potential color loss. Mix the determined amount of clay in water and add to the tank and stir like crazy.

Cold Stabilization

Tartaric acid is the most prominent acid in wine with the majority of the concentration present as potassium bitartrate. During fermentation, these tartrates bind with the lees, pulp debris and precipitated tannins and pigments. Usually about half of the deposits are soluble in the wine, but on exposure to low temperature they may crystallize out unpredictably. In simple terms, prior to serving your white wine you decided to pop it into the freezer for a bit and when you pull it out, there are crystals or wine diamonds floating around in your wine UGH! These are all quite harmless but may seem quite unsightly and in some cases might be interpreted as a fault in the wine. To ensure this does not happen to any of our loyal customers, we freeze the tank of wine, precipitating the acid out and ensuring the wine is stable at a much lower temperature that you would cool the bottle down to. For our whites, we normally hold the wine at 28 degrees for 10 days or so.

cold stabilizing the wine at 28 degrees


So while fining refers to binding to certain particles in the wine, filtration works by passing the wine through a specific media, essentially trapping the particles. This word seems to strike fear in the hearts of consumers, it sometimes borders on blasphemy, heaven forbid a wine is filtered. I think this stems from the notion that wine is really natural and any or all involvement by chemical or machine, really does the wine a heavy injustice.

If we were talking about red wines, then I could argue both ways on the pros and cons of filtration, but since we are dealing with whites and a Rose’ for this bottling, there is no question, filtration is necessary.

Let’s break it up into 2 parts.

Firstly there is no doubt that filtration adds to the aesthetic quality of a wine. A white wine that has gorgeous clarity is far more appealing than one that is grainy and cloudy. That’s not to say you cannot bottle a chemically stable wine without filtration but we live in an age where opinions on things are made firstly by sight, and then ultimately taste.

the difference between filtered and not, can you guess which is which?

The most important factor in filtering our whites though, is one of chemical stability, ensuring the integrity of the wine for the consumer across each and every bottle.

Since each of these wine contains small amounts of sugar and have not allowed to undergo secondary fermentation [malic acid turning into lactic acid], we need to remove any bacteria or yeast that could cause fermentation in the bottle. Since fermentation produces carbon dioxide, our still wines might all of a sudden become sparkling, surprise!

To that end we pass the wines though as series of filtrations, each time passing the wine through a tighter porosity, until we reach 0.45 micron, widely accepted as sterile filtration. There are many ways in which to filter the wines, plate and frame, diatomaceous earth and cross flow filtration. For a small to mid-sized winery such as ours, we use a plate and frame filter which is more than adequate for our needs. It very much works like a coffee filter, whereby the wine is pushed through a 40×40 sheet comprised of cellulose fibers, trapping anything that is bigger then the porosity of the sheet. This process is slow, and we have to be very mindful of not blocking the filters, hence the multiple passes over the course of a few days.

our plate and frame filter

A few tests and sulfur adjustments later and Bam, new wine on the market for the customer to enjoy.

Of course we are biased but we are excited about the 2012 wines and cannot wait to share them with you. So as we roll out the newest class, I just want to thank everyone for their continued support, all of us at Keswick Vineyards really do appreciate it.


Stephen Barnard