Cork Variability, MLF Question, pH Testing, and Aceto Problems

I hope it’s OK if I take a question a bit out of the home winemaking realm, but maybe your readers will find this of interest. We use a hand-corker to cork our homemade wine, but when we bought a mixed case of wine for a party from our usual local wine shop and brought them home, we noticed that a couple of the bottles seemed to have the cork pushed up a few millimeters above the lip of the glass bottle. The bottles in question were two totally separate wines.

We know from our own home winemaking experience that sometimes the plunger on our hand corker can make the depth to which the cork is pushed vary a little from bottle to bottle. However, in commercial wines, does this mean anything? Is there anything wrong with the wine? Thanks for any of your wiz-dom on the topic!

Emily Robinson
San Jose, California

You’re absolutely right, raised corks can either be a problem (if they’re too high, or too high of a percentage from bottle-to-bottle) or it could be nothing at all. The devil is in the details and finding out why. Bear with me while I break down a few possible causes and their implications of what you discovered in your mixed case:

Possible causes

1. Uneven screwing-down of the plunger guides on the bottling line.

This happens when the plungers (controlled by the automatic machinery on the bottling line) don’t quite push the cork in all the way. Usually a slightly raised cork is caught by the workers overseeing the bottling line, and they make adjustments during the run to get the corks to line up with the lip of the bottle (or a few millimeters below) for the remainder of the bottling run. Bottling lines consist of many pieces of machinery that must operate in synchronicity and every commercial bottling start-up is an art and science of making minute adjustments until all the parts (rinser, filler, corker, capper, labeler, packer, etc.) run in concert. There will be natural variations in every bottling run and every bottling line, it’s just a question of how quickly everything is “run in” to spec by the crew.

-Verdict: No big deal unless there is a high percentage of raised corks per case or pallet or some of the corks are sticking out so much that the bottle tops look like mushrooms, out of desired specifications. It is purely a visual packaging issue and doesn’t mean the wine is spoiled or compromised in
any way.

2. Wine was exposed to heat during transport.

Higher temperatures over time during transport can cause the headspace gas (usually a mix of air and nitrogen, depends on the bottling line sparging treatment) in the bottle to expand, pushing corks outwards. If it appears, this defect usually presents in transport batches, where for instance an entire truckload will be affected to a similar degree. This defect is less likely if there is high variation of degrees of raised corks within a case or at random over a pallet. To investigate if heat exposure was the cause, clues can be found if there is evidence of entire batches being raised, i.e. investigate if a pallet or truckload was broken down to discover if there was homogeneity in heat exposure.

-Verdict: Potential that wine quality has been negatively impacted. You need to taste the wine to see if it tastes cooked or visually has turned brown, all signs of premature heat oxidation in the bottle.

3. Wine is experiencing microbial activity in the bottle.

If the wine was not sterile filtered, or if the sterile filter on the bottling line is compromised at some time during the run, corks can push due to re-fermentation (could be bacterial or yeast, yeast is more likely) in the bottle. Since you’re not experiencing this in every bottle in a batch, batch sterile filtration failure is likely not the cause. Further investigation/information is needed as to %, number, and distribution of pushed corks. It’s possible random bad corks (maybe poorly re-expanding in bottle) have caused oxygen to enter in only some of the bottles, triggering a microbial bloom if there is a food source for those organisms, as follows: It’s possible in the case of a sweet wine or a wine that is not ML complete because in each of these cases, the wine is offering “food” (sugar, malic acid) to microbes. If conditions are right, random refermentations are possible.

-Verdict: If a re-fermentation is present, this is a potential issue because you may note if the wine is fizzy or cloudy due to the refermentation and corks may push further out and more bottles may become affected over time. Microbial analysis and sensory analysis of a good sampling of multiple bottles would help to settle if this was the cause or not, but since you bought a mixed case you’re not about to go back to the store and do this, right? Since you can’t tell if every bottle of that particular kind is affected, more information is needed to investigate the source/reasons.

I wouldn’t be surprised to see a few bottles in any given large bottling run have corks slightly above the bottle lip but it’s certainly a problem if corks have pushed over time, or if it’s an unacceptable incidence/percentage. As you recognize with your home winemaking and home hand-corking, it’s easy to get bottle-to-bottle variation. However, if for those wines that have pushed corks all of the bottles from the shop are like that, it’s an indication something may be wrong with those bottles from the get-go. Since you bought your wine from your local shop, you might want to give your shop owner some feedback, especially if you know him or her and especially since it sounds like you’re a repeat customer.
Maybe they can contact the producer and do a little digging for you. At the very least, I as a winemaker would appreciate the feedback if all of a sudden my corked bottles started pushing up in the marketplace!

After primary fermentation and pressing my red grapes, I will be placing the juice into my stainless variable lid tank. In a few days I will start the secondary fermentation. Do I need to add metabisulfite when I place them in the tank or will that affect my ability to start the secondary fermentation?

Frank Lamorte
Carmel, New York

That’s a great question with a very simple answer. You should not add postassium metabisulfite (SO2, or sulfur dioxide) to your wine between primary and secondary fermentation. Because the SO2 will inhibit or could completely kill off the bacteria you need to conduct the secondary fermentation, it’s critical that we never add SO2 to wine at this time.

Malolactic bacteria are very sensitive to sulfur dioxide and your malolactic fermentation (aka “secondary fermentation”) could be completely inhibited. You may add a little bit of SO2 (up to 30 ppm) when you crush, to ward off spoilage organisms that might be antagonistic to the yeast you want to conduct your primary fermentation. But by the time the wine is fermented until it’s dry, this sulfur dioxide will be mostly, if not completely, in the bound form and not able to interact with any malolactic bacteria you might be adding to conduct your secondary fermentation.

There’s no reason for you to wait between the end of primary fermentation and inoculating for your malolactic fermentation. If you must wait for some reason, however, you should be ok if you drop the lid on your variable tank down on the wine surface to exclude air. The residual carbon dioxide gas in the fermentation should help keep the wine protected. Inoculate with your malolactic bacteria as soon as you can, though, and be sure you keep the next SO2 addition until after your malolactic fermentation is complete.

How long after adding acid blend and mixing should I wait before re-testing my pH? I’ve not been able to find this information in past articles.
Jack Kerr
Santa Fe, New Mexico

The answer to your question depends on the size of your batch. The bigger your batch, especially if it’s must all mixed together with juice and skins, you need to mix quite a bit longer. Let’s say for example you have a 5-gallon (19-L) carboy of Chardonnay juice and you are adding 1 g/L tartaric acid dissolved in a little water, then you could probably stir the solution into your carboy with a stirring rod for about a minute, let it sit for about 30 minutes and then re-sample. For a big 60-gallon (227-L) trash can full of must, it’s probably a good idea to do a good 5-minute punch down, wait 30 minutes and do another one before re-sampling for a pH or TA test. It is very important that you mix your containers well before re-sampling. The chemical effect of dissolved acid blend on pH is immediate (with complete stirring). I hope this gives you some good guidance.

My dry Merlot has been aging in a carboy in my garage for about four months. I made a kit and have racked it two or three times now. The wine has recently changed and not for the better. I’m noticing a distinct vinegar aroma whenever I un-stop the carboy. What is this, can I fix it, and is there any way to prevent it happening again?

Mike Rodriguez
Fayetteville, North Carolina

Well, it seems like you have been paid a visit by a colony of Acetobacter, aka acetic acid bacteria. They love air, eat alcohol, and turn it into carbon dioxide and vinegar. Not fun. The biggest issue is that no matter what, once you’ve got them and they’ve produced a certain amount of acetic acid, (aka “VA” or volatile acidity) there’s little you can do to remove it from your wine. Bigger commercial wineries can hire in reverse osmosis filters to remove some of the VA for you, but sadly home winemakers make far too little volume to make this kind of treatment worthwhile.

The only option really available to you is to blend this carboy out with other wine to lessen the level of the vinegar smell. However, you and my loyal readers might know that I always advise you to never “blend a loser” i.e. don’t throw good money after bad. If you don’t love the new blend then you may be better off just tossing the offending Merlot batch and making a new one. That’s the beauty of kit winemaking after all, you can make wine any time of year when buying a kit off the shelf instead of relying on grapes.

So what can you do in the future to ward off future attacks of the sneak Acetobacter? Read on for some handy tips.

— Make sure your SO2 (sulfur dioxide) levels are high enough and are appropriate for the pH of your wine. SO2 becomes less effective as the pH rises, so for red wines, especially, (which tend to be lower acid- or higher pH- than whites) it’s important to store wines with at least 28 ppm free SO2.

— Be sure your pH is in the “safe” range not just for sulfur dioxide effectiveness, but because acidity naturally inhibits Acetobacter, which love a higher pH environment. I try to keep my red wines under 3.65 pH. It’s OK to add tartaric acid after malolactic fermentation if you need a little tweak downwards.

— Keep dry wine completely topped up, i.e. in completely full containers. Young wines like yours are especially vulnerable to Acetobacter attack since the protective layer of carbon dioxide gas produced during fermentation is no longer there. Here’s a trick for if you don’t have a completely topped-up carboy: Pitch some washed, dried glass marbles (or glass decorative pebbles, often found at a nursery or home decorating store) into your carboy. They’ll sink to the bottom and displace air, forcing the level of the wine up into the neck of your carboy. Just don’t use decorative rocks, even if they are round and clean — there’s no way of controlling what kinds of heavy metals or other undesirable toxic compounds could be leached into your wine!

— Immediately clean up spills and messes in your wine storage area. Having any kind of food (puddles of wine after racking, anyone?) for bacteria and spoilage organisms to munch on will only increase the chance of them getting a foothold in your winemaking area.

— Keep all equipment as clean as possible, even between uses.

— Watch wines that have lower alcohol levels, especially if they are under 10%. Alcohol acts as a natural antimicrobial agent (the reason why Saccharomyces produces it) inhibiting spoilage bacteria. If your Merlot is particularly lower alcohol, this could be a contributor to an Acetobacter outbreak.

— See a fruit fly? Try to get rid of Drosophila melanogaster as soon as you can. The best ways to control these little buggers that can carry all sorts of nasty spoilage bacteria on their dirty little feet is to exclude them from your winemaking environment altogether. They need a food source to survive so, as per above, make sure you’re cleaning up spills promptly and are getting rid of any sources of standing water. Make sure your winemaking and wine storing areas are completely screened off and if possible try to have some kind of positive air-displacement mechanism if you can manage it. I’ve even found that a fan positioned so it blows towards a door can help push these guys back and keep them from entering every time the door is opened.

—Store your wines in a cool, dry area. Lower temperatures and dryer humidity discourage acetic-acid causing bacteria as well as other potential spoilage yeasts and fungi.