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Sean Brock Asks Dave Arnold: On Aging Bourbon & Blanching

Welcome to Ask Dave Arnold, a regular feature in which David Arnold, director of technology at the French Culinary Institute, provides in-depth answers to questions on food science, cooking technique, and other issues. For this installment, Sean Brock, chef at Charleston, South Carolina restaurants McGrady's and Husk, has posed the queries.

[Original artwork by Eric Lebofsky]

Question One: It's no secret that I am a bourbon lover. Is there any way to speed up the aging process or to simply improve it? What about putting charred wood pieces in the whisky and putting that into a vacuum chamber and forcing the liquid in and out of the charred oak? Trust me, I understand, love and appreciate the entire bourbon process, but what if we could take ten year-old bourbon and make it taste like twenty year old bourbon in a matter of days or months? Just curious, I realize it's blasphemy. Is it possible? I would be happy to be your taste tester if you were to test this theory.

Dave Arnold: Speed aging is a highly controversial matter. Many people try to quick-age wine or spirits by using smaller than normal barrels or by macerating with charred wood staves (the pieces of wood the barrels are made from), or charred wood chips. They can't achieve the exact same flavors that come with traditional ageing.

What is going on during traditional barrel aging?

· Colors and flavors are extracted from the wood (like a regular infusion).
· Wood, liquor, and oxygen in various combinations break down old compounds and create new ones.
· Liquids and volatiles slowly evaporate from the cask.

Accelerated aging usually focuses on extracting color or flavor from wood. The theory is simple: increase the surface area of liquid in contact with wood and you speed up aging. One way to increase surface area is to use small barrels. As the barrel size shrinks, the volume decreases much faster than the internal surface area does, so small barrels have more wood contact per gallon than larger barrels do. Traditional bourbon barrels hold about 53 gallons. A 5.3 gallon barrel of the same proportions has more than twice the wood surface area per gallon of spirit. Another way to increase wood contact is to just add wood — whether you have a barrel or not. Wood staves can add surface area. Unlike a stave in a barrel, a stave placed into liquid has contact with spirit on all four sides instead of just one. You can go further. Wood-chips or shavings provide the most surface area per pound of wood you could hope for, short of sawdust.

What you get from all that extra wood contact is rapid extraction of wood flavor and color. Quick aging is, therefore, partially successful. Your idea of using a vacuum machine to force liquor in and out of the wood chips would definitely accelerate the extraction of oak flavors. I have also used my rapid nitrous infusion technique to get oak into booze quickly. BUT? oak extraction isn't the only thing going on in barrel aging.

Traditional aging relies on the small amount of oxygen that permeates the pores of the oak barrels. Smaller barrels, like their larger cousins, let in oxygen, but at a different rate per gallon of spirit. Aging in sealed tanks with wood chips blocks all external oxygen. People have attempted to mimic natural aging in tanks by adding tiny controlled amounts of oxygen to the liquid (called micro-oxygenation). Results have been mixed, at best.

Barrels don't just add flavor, they change it – something that I prove by removing the oak flavors from aged spirits. I redistill aged bourbon and scotch, removing the mostly non-volatile oak compounds from the whiskeys. I do my distillations at low temperature under a vacuum in a rotary evaporator and lose very little flavor in the process. I then taste the de-oaked distillates next to those same spirits un-aged straight from the still (bourbon people call this un-aged liquor white-dog, scotch people call it cleric). The results are amazing — the notes of corn in bourbon white dog and malt in scotch cleric are highly mollified and altered in the aging process. You can read about one of those experiments here.

Turns out, time is an essential ingredient. It is hard, if not impossible, to get all the traditional aging reactions to take place quickly but in balance. I don't think you can reproduce the effects of 13 years of aging in a matter of months. That said, even if quick aging isn't the same as long-term aging, it just might be delicious! That is for the taster to decide.

There are at least two commercially available products that use increased wood contact aging:

· Tuthilltown Spirits in upstate New York is well known for aging in small barrels. Their flavor profiles are built around the small-barrel taste. Tuthilltown was purchased recently by William Grant, the good people that bring you Hendricks gin, so Tuthilltown's production is being ramped up which means that they will have to start using some larger barrels. I have been told that even though they will be using some larger barrels, they will always try to maintain their current taste profile by blending in some small-barrel liquor.

· Maker's Mark 46 is a bourbon that is aged traditionally, but has a specially toasted fresh stave added to the barrel towards the very end of the aging process.

Question Two: When dealing with fermenting food like cabbage for sauerkraut, why do old timers say to check the almanac first? They say to make sure that the signs are above the belt, preferably in the head, and the moon is new. I know people who swear by this. Does it have any validity?

Dave Arnold: When it comes to planting or harvesting, it is entirely possible that moon cycles can have an effect. Plants might respond to extra light, for instance. I don't think enough research has been done to know. But I can't think of any specific effect the phase of the moon would have on sauerkraut fermentation, or fermentation of any kind. I suppose it is possible that the proportion of various wild lactic acid bacteria (the group of bacteria that produce delicious sauerkraut) changes with the phases of the moon, but I have no evidence, even anecdotal, to show that it does. On the other hand, it seems plausible that cabbage harvested during a particular phase of the moon might be better or worse than cabbage harvested at other times — in which case the sauerkraut made from it could be better or worse.

Time of year can easily influence sauerkraut quality. In the days before climate control, the time of year greatly influenced the fermentation environment. Additionally, sauerkraut from cabbages harvested at the peak of flavor will be best. So there is probably a best time of the year to make sauerkraut. Remembering the perfect time of year based on zodiac signs or other astronomical events makes sense because those events provide repeatable yearly milestones –equivalent to dates on a calendar. A calendar would be just as useful.

Old-time wisdom is based on generations of observation. Dismissing it out of hand is a common and unfortunate mistake. Just because we don't understand why something is true doesn't mean it isn't true. We need accurate studies to see if old-time concepts have practical validity. When scientists investigate these sorts of claims, they sometimes find that the old wisdom is based on some valid but hitherto scientifically unnoticed process or factor.

And sometimes they find the old wisdom is just hokum.

Question Three: For as long as I can remember, I have been obsessed with keeping green vegetables green during the cooking process. When I was in culinary school I had Thomas Keller's essay on "Big Pot Blanching" (from The French Laundry Cookbook) memorized. I would stare at the pot of asparagus blanching and wait for the exact moment for the color to change before pulling them. I always wondered what the exact internal temperature was. Is there an exact temperature? If so, can we set water baths at specific temperatures and get perfect green vegetables every time? Is this wishful thinking? Our friends at Ideas in Food also introduced us to Cryo-blanching years ago. When you vacuum seal asparagus on the highest setting with a little salted asparagus juice and freeze it, the color seems to be just as vibrant as blanched asparagus when thawed. Would you mind explaining the color change during the freezing/vacuum process? Is it better than blanching?

Dave Arnold: For people not hip to the problem we're discussing:

Blanching is where foods are cooked or par-cooked in boiling salted water, then shocked in cold water to stop the cooking process. You blanch for several reasons:

· To cook or par cook in advance so that you can quickly finish dishes later, right before serving
· To kill enzymes that cause discoloration in raw foods — think potatoes and herbs
· To get vibrant colors in veggies

Here's what happens to colors when you blanch:

Vegetables are full of air pockets. Those air pockets scatter incident light and make the vegetable appear duller than it would if those pockets were filled. As the vegetable begins to cook, the air pockets rupture and collapse or fill with water. Without the air pockets, light scatters less and you see more of the pigment: green veggies look greener, carrots look more orange.

The temperature at which you blanch is important. Vegetable structure begins to soften around 85 C (185 F), but with green vegetables you should use a higher temperature, like 100C (212 F), so you can cook faster. Speed is key because although the heat ruptures air pockets and initially makes your veggies look brighter, this same heat will, over time, break down green chlorophyll and produce dull, unappetizing hues. The longer it takes to cook a vegetable, the more chlorophyll you break down.

Blanching is a race — heat fast to brighten and cook, then cool quickly to prevent heat from ruining the color. This is why we shock veggies in cold water to arrest cooking. Ice water works great for shocking because ice has fantastic chilling power. Tap water is sufficient for small product amounts.

Don't add acids to your blanching water, or to your finished vegetables, if you want to preserve color. Acid is the enemy of chlorophyll, accelerating its breakdown. Many people only blanch with uncovered pots because they want certain volatile acids in the vegetables to boil off rather than remain in the pot — I don't know if that extra step really helps. In any event, never add acidity to a green vegetable until you are about to serve it.

Do add salt to your blanching water. Salt is the friend of chlorophyll. Salted water prevents color and flavor from leaching out of vegetables while cooking, and adds flavor to porous vegetables. Contrary to popular belief, salt does not appreciably raise the temperature of the boiling water (it raises it a little, but not enough to make a difference).

The "Big Pot" blanching referred to in the question uses a large amount of highly salted water at a full-tilt boil. The volume is to keep the temperature up, the salt is to improve taste and protect the chlorophyll.

So to answer the first part of your question: the hotter the temperature the better when it comes to blanching green vegetables. If you are blanching veggies in a vacuum bag, add some liquid to the bag so that the vegetables cook more quickly. If the veggie isn't green, you can cook longer at lower temperatures – but I doubt there are many advantages to be had (although you can get a super sweet flavor and bright orange color in a still-crunchy carrot by cooking for 24 hours in a vacuum bag with some liquid at 60C/140F).

There isn't an optimum internal temperature for achieving great color –just pull the veggie when it is done.

Vacuum Infusing/Vacuum Compression is technique where the air is sucked out of the vegetable using a vacuum machine in a vacuum bag. When the bag is sealed and the vacuum is released, those air pockets we talked about earlier are either crushed by the force, or, if there is liquid present, are filled with that liquid. Both the crushing and the filling can brighten colors. Cucumbers treated this way look like jewelry.

Cryoblanching is a term coined by our friends at Ideas in Food to describe when veggies are sealed in a vacuum bag (compressed and perhaps infused if liquid is present) and then frozen and thawed. As the vegetables freeze, ice crystals are formed — typically on the outside of plant cells, causing dehydration. Not all of that water is re-absorbed when the veggie thaws, so the veggie gets limper. Those ice crystals also puncture cell walls, breaking down the tissue so the veggies get more tender. The combined effect of vacuum and freezing causes enough tissue damage to brighten the color and soften the texture. Repeated freeze-thaw cycles will cause further tissue breakdown.

Cryoblanching leaves the veggie tasting raw, with a blanched look and texture. Remember that cryoblanching will not kill enzymes, so veggies and herbs that discolor because of enzymes — like artichokes and basil — won't be protected by cryoblanching.

And for more answers to your cooking issues, tune into Dave Arnold every Tuesday at noon on the Heritage Radio Network

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