Barrel

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Jason Sledd's barrel and bulldog [1]

in progress

Barrels are wooden fermentation vessels which are an ideal vessel for fermenting many funky and mixed-fermentation beers. Many of the best mixed fermentation beers are aged in oak barrels or foeders. This page discusses the sorts of barrels and barrel alternatives available to pro and home brewers and influences those barrels have on the final beer to help brewers choose the barrel or barrel alternative that is right for them. In addition, this page gives some suggestions for using and taking care of barrels.

Types of Wood Used in Barrels

The type of wood used to make a barrel can impact both the flavor compounds that the barrel can provide as well as the rates at which gasses (O2) are allowed to penetrate through the wood. The characteristics of a given wood are dependent on the species used but also on factors such as more local conditions where the wood was grown in addition to the seasoning and toasting process. Toasting is discussed further in its own section below.

Acacia

Acacia wood, also known as "Black Locust," is a species of tree native to the southeastern United States - although its roots have spread worldwide, from Europe all the way to Asia and as far south as Southern Africa. More recently, Acacia has been used as an alternative to the traditional white oak when aging White wine.

Although white wine is often aged in steel casks, wine makers have since discovered that aging in an Acacia barrel preserves the wines aromatic and fruit characteristics. Acacia wood does not contain as much tannin content as oak, thus, it better preserves freshness as well as floral and varietal characteristics. Additionally, white wines aged in Acacia barrels do not suffer from a loss of overall structure. Acacia wood is well suited for aging White wines as it does not contribute the stronger flavors one may find in oak, which may overwhelm a white wine, while stiff allowing a small amount of gas transfer.

American White Oak

American White Oak (Quercus alba) is regarded as one of the preeminent species of hardwood grown here in the United States of America. This species of White Oak has tyloses, an outgrowth of the parenchyma cells which stems from a reaction to natural stresses in the environment such as drought; which gives the wood a closed cellular structure, making it water- and rot- resistant. This closed structure also results in less air transfer through the wood than other oak types such as French oak.

Within the Wine & Spirits industry, Quercus Alba or American White Oak is the primary source of material in the production of Whiskey barrels (especially in the case of bourbon, which is legally required to be aged in charred new oak barrels). What makes this species of wood key to the whiskey industry is it chemical structure and the effect this imparts on the aging whiskey. American White Oak is known for its high vanillin content, oak lactone (coconut/bourbon characteristic), and wood sugars which all affect the bourbons taste. Additionally, American White Oak affects the coloring of the bourbon itself. Impure wood varieties like Pine contain resin canals which pass strong flavors into maturing whiskey. Note that the char levels in some spirits barrels might make them a less ideal candidate for many mixed-fermentation beers. In addition, some bourbon barrels are not constructed as sturdily as wine barrels [2], possibly due to the inability of producers to use barrels for many subsequent batches of bourbon (as would be common in wine).

French Oak

French oak (Quercus sessilis/Quercus petraea and Quercus robur) contributes comparatively more trans-3-Methyl-4-octanolide while American oak contributes more cis-3-Methyl-4-octanolide to beer [3]. These lactones both contribute a coconut character but the cis-lactone has a much lower flavor and aroma threshold [4], therefore American oak barrels may give more of a lactone flavor and aroma impact. Q. sessilis is more common in wine aging and Q. robur is more common for cognac barrels [3]

Hungarian Oak

(Quercus frainetto)

Romanian White Oak

Chestnut

Chestnut (Castanea sativa) can be a cheaper alternative to oak for barrels. Chestnut barrels are used by some lambic producers (though generally most lambic barrels are oak). Chestnut allows more gas permeability than oak, and therefore will allow more oxygen transfer than a comparable barrel made out of oak[5]

Barrel Alternatives

in progress

A number of wood products are available to homebrewers to get wood characteristics without using a barrel. While barrel flavors are generally not the primary goal of funky beer brewers who use barrels for fermentation and aging, wood can contribute some of the additional characteristics that barrels offer (such as mouthfeel influences) and can also be used to house microbes in a similar way to a barrel (Vinnie's dimebags). The most common non-barrel wood products available to brewers are oak based.

Chips - Oak chips maximize surface area and have less variability in the depth of toast. Oak chips are not ideal because if the brewer is after flavor contribution chips will be more one dimensional and if the brewer is not after a wood flavor contribution, oak chips will give faster flavor extraction than other options and will therefore not give the other benefits of oak as well as other products.

Cubes - Oak cubes are readily available to brewers. They offer greater toast complexity and a lower surface area to volume ratio than chips. (reference Vinnie's dimebags, amos oak in primary)

Rods - Rods offer a similar product to cubes however the surface area to volume ratio is even smaller. In addition, rods (and lumber) are the primary source for alternative woods. See John Gasparine's 2013 NHC presentation on alternative wood aging (AHA membership required).

Spirals - Wood spirals are basically rods that have been shaped to increase the surface area. They offer the same potential benefit as rods and cubes in dimension of toast flavor. Based on faster flavor extraction than rods, spirals may not be the ideal choice for brewers looking for the non-flavor benefits of wood.

Honeycombs - Honeycombs are similar to oak spirals in what they offer and they maximize the surface area even more.

Lumber Stores - Some woods traditionally used in barrels such as oak go through a prolonged curing process before being formed into a barrel and toasted. If you are trying to use one of these woods, be aware that just getting wood from a lumber store and toasting it yourself will not give the same results as properly cured woods used to make barrels and barrel alternative products. Lumber stores can be good resources for finding some 'exotic' non-traditional woods to use in their beers. For brewers interested in this we recommend this presentation from the 2013 National Homebrewers Conference given by John Gasparine (must be an AHA member to access). Note that some woods may contain compounds not safe for consumption so be careful and research your woods before you use them.

MTF Member Usage Suggestions

We'd love to hear your experiences! Please contribute them in this MTF Facebook thread.

Pre-treatments refers to anything the brewer might do with the barrel alternative before putting it in their beer (such as boiling, soaking in boiling water, soaking in wine or spirits etc.). Some brewers prefer pre-treatments to remove some of the more aggressive character of the wood and approach the sort of semi-neutralized barrel character that brewers might achieve from use of second hand wine or spirit barrels.

Wood Type Toast Level Format Amount Pre-treatment Contact Time Oak presence/Notes
American Oak Medium Toast Spirals 0.33*1x8" Spirals per gallon [6] None 6-12 months noticeable vanillin
American Oak Medium Plus Toast Spirals 0.33*1x8" Spirals per gallon [6] None 6-12 months noticeable vanillin
American Oak Medium Toast Cubes 0.4 oz per gallon [7] Boiled 11 months Could have used more oak. Note that the base beer was rather assertive.
French Oak Medium Toast Cubes 0.15-0.25 oz per gallon, depending on beer color/strength [8] Boiled Used cubes also re-used in 50-50 blends with fresh in subesquent batches
French Oak Bordeaux Blend (4 toast levels) Spirals 1.16" long spiral per gallon [9] None 1-3 weeks good tannin
French Oak Light Toast Spirals 1.16" long spiral per gallon [9] None 1-3 weeks Some structure, but otherwise not noticeable
Various Woods (Black Swan Barrel Alternatives) Honeycomb 1" long honeycomb per gallon [10] none 6 weeks May not be suitable for clean beers

Non-Wood/Steel/Plastic Vessels

Alternative vessels include Amphorea and food-safe concrete vessels used in wine making.

Toast level and Volume

In progress

Barrels and barrel products are generally available in toast levels of light, medium, medium+ and heavy as well as varying levels of char. in addition to different wood types, different toast levels each have their own characteristics and are chosen for different purposes. Barrels used for aging spirits such as whiskey generally have some degree of charring, or at least heavy toast, while red wine barrels may be more commonly in the medium or med+ range. While the homebrewer and professional brewer does not always have full control over the toast levels of the barrels that they are getting (as the barrels are frequently used by wine and spirit producers before being acquired by brewers), brewers will likely find that different toast levels are better suited different beers.

Some brewers select specific barrels based on what they previously held as a fundamental component of certain beers (e.g. Russian River, Cantillon 50N, 3F Zenne). In addition, sometimes brewers aren't looking for barrel flavor in their sour beers and are more interested in the medium that barrels provide for fermentation in addition to some less flavor active compounds that barrels may contribute (--source: Jay and Tim Clifford for on the sour hour, probably something from JvR). Due to the delicate balance that good mixed-fermentation beers have, an aggressive barrel character may not always fit and brewers will have to get a feel for their barrels to know how long it takes for a beer to develop appropriate barrel character compared to how long until it develops the right fermentation character. For a first fill, it is recommended to taste the beer regularly to see how it is developing, and it may be necessary to allow additional aging in other vessels like carboys or stainless tanks for the beer to arrive at the right level of both fermentation development and barrel that the brewer is targeting.

---flavor description table to come (see also the flavor descriptions for different wood types above)----

Barrels are also available in a number of different volumes. Typical volumes of wine barrels are around 228L (60 gal) and may vary slightly depending on region and cooper. Professional breweries generally use barrels of this volume and larger. For homebrewers, filling a barrel of such volume can be a bit more tricky and may require a group effort and/or many brews. Some smaller barrels are available for homebrewers via craft distillers (among other producers). These barrels which can be found in the 5-15 gallon range provide an attractive option for homebrewers though some special considerations may be needed.

First, smaller volumes mean a greater surface area to volume ratio. This means that both flavor extraction from the barrel will be faster and O2 pickup will be greater (as oxygen penetration is tied to the barrel's surface area). Both of these factors make these small barrels attractive to craft distillers as they can shorten the aging time for certain flavor developments, but for the homebrewer looking to produce long-ages mixed-fermentation beers with no barrel flavor impact to supportive barrel character rather than strong barrel character this is not ideal. The barrel character can be partially stripped by repeated use and soaking with water. Because many of the small barrels available to homebrewers are derived from distilleries and therefore may be more likely a heavier toast level, it may take longer to remove the character of the wood and a progression of beers may be needed to make the barrel appropriately neutral for long aged sour beers [11].

Second, the staves of smaller barrels are generally thinner allows greater oxygen permeability. So smaller barrels, both by surface area to volume ratio and by generally thinner staves, allow greater O2 transfer to the beer than larger barrels. Homebrewers may wish to counteract this O2 transfer by waxing smaller barrels [12], topping up regularly, keeping humidity around 40-50% and temperature as steady as possible, and aging for a shorter amount of time (1-3 months).

1-5 Liter Barrels

There are also various barrels on the market that are very small (1-5 liters). These barrels are designed as novelty items or perhaps aging spirits where oxygen exposure might not be as big of an issue as it is for beer (especially sour beer). The problems of a low volume and a high surface area expressed above are an even greater a threat when aging sour beer in such a small barrel. Although aging for a very short amount of time in these very small barrels (perhaps 1 month or less) might produce favorable results, we recommend against aging sour beer in barrels that are smaller than 5 gallons (19 liters). Some people warn that the manufacturer of these small barrels uses very thin staves even for their larger version (20 liter). They are sold by a large number of outlets, and can be identified by their spigot and dot in the center of the head [13].

Using Barrels for fermentation and/or aging

in progress

Should you top off or not? Yes (Tilqiun, Rare Barrel) No (Rare Barrel[14](~7 minutes in), Jester King[14](~7 minutes in), Crooked Stave, The Bruery)

How long should you leave a beer in a barrel? The aging time will depend on what sort of beer you are making, what your desired outcomes are, and the characteristics your barrel gives. Belgian lambic is aged in barrels upwards of 4 years with no ill effects. Other beers can go through a barrel primary fermentation or very short aging and be out of the barrel in weeks to months. The longer you age a beer in a barrel, the more barrel character you will extract (in terms of both flavor and tannin structure). This is probably of secondary importance to how much the barrel has been used/how neutral it is, so keep your individual barrel characteristics in mind when determining aging time. Generally, producers of mixed fermentation beers do not report noticing problems from autolysis in prolonged aging on yeast sediment [14](~9 minutes in).

Andy Parker from Avery Brewing Co., in discussing non-sour beer in barrels, says that they get complete extraction of flavor from barrels within 2 months. After four months, effects from oxidation can be detected, and after twelve months the more porous barrels display heavier effects from oxidation. Parker recommends removing the beer from a barrel based on the effects of the oxidation of individual barrels (in sour beer, this could have an affect on the perception of acetic acid and ethyl acetate, as well as other oxidative characteristics such as sherry notes, depending on the style of the beer) [15]. Sour beer generally takes longer to mature in barrels due to the microbial activity, however this advice might still apply to sour beers in certain barrels that are experiencing too much or very fast oxidation due to being more porous than other barrels.

Should you clean your barrel after every use? Jester King reports preferring barrels that get a bit more yeast in them (when using barrels as secondary vessels) and they may use barrels for 2-3 subsequent beers before rinsing out the trub [14](~9 minutes in, ~16 minutes in).

Modifying barrels

Barrels can be modified to operate as tanks such as mash tuns:

Fruit Flies

Barrel Care

in progress

Swelling barrels

Swelling barrels involves soaking the heads and/or staves of a barrel with water to cause them to swell up and form a tight seal. If a barrel has been stored dry, it might be necessary to swell the barrel, or at least leak test it, before filling it with beer. The Rare Barrel swells barrels in a couple of different ways. When they are not worried about preserving the character of what was perviously held in the barrel, they fill the barrels with water without storage chemicals for a maximum of 48 hours before changing water if the barrel is not fully swollen [16] (~33 minutes in).---To do--- external swelling (ref rare barrel, Tilquin head swelling, Todd Ashman Eclipse).
External swelling can be done by placing a barrel on its head and cover the upward facing head with hot water for several hours. Flip the barrel on its other head and repeat. This process swells the heads which in turn pushes the staves tighter together in the hoops.
Although impractical for homebrewers, commercial brewers and wine makers can use steam to swell barrels [17]. Steamed barrels should be allowed to cool before bunging; cooling with a bung installed can lead to imploding barrels [18]. Steaming can also be a technique for cleaning used barrels.

Cleaning

Some producers remove heads from barrels during cleaning. This may be beneficial if whole fruit is used in the barrel [19]

It is advised not to use water that contains chlorine or chloramine to clean barrels. The residual chlorine or chloramine may not be enough to impact flavor directly once emptied from the barrel, but these chemicals form hypochlorite [20] [21], which is one of the two things needed to cause 2,4,6-trichloroanisole (TCA). The second thing needed to produce TCA is mold. TCA is a common off-flavor in the wine world, and is described as "moldy, musty, cork taint" [22].

MTF barrel cleaning threads:

Sanitizing

(In Progress)

Effects of heat sanitation results by Fabrizio et al (2015).

Ozone has been shown to be an effective way to kill Brettanomyces that is buried in the wood of oak barrels (it has been found to burrow as deeply as 8 mm into oak barrels), but the ozone must be applied for an adequate time to allow for the ozone to diffuse into the oak. The amount of time needed to completely kill Brettanomyces living within barrels with ozone is not known, but it was found that 30 minutes of exposure to 40 mg/m3 ozone concentration was not enough time [24]. The concentration of ozone is known to be a more important killing factor than time, therefore some recommend filling the barrel with liquid ozone, or rinsing with hot water first to open the pours of the wood and then rinsing with ozone liquid [25][26].

The most effective and preferred method is to heat the inside of the oak barrel to at least 140°F (60°C) for 20 minutes with hot water or steam. This has been found to be an effective way of killing Brettanomyces within the wood of 3-year old barrels infected with Brettanomyces. Note that this might not be hot enough to kill other heat tolerant microbes, however these heat tolerant species tend not to be beer spoilers. Treatments that are higher in temperature and longer should be fine with steam, however if hot water is used then the longer the water is exposed to the barrel the more character from the barrel that gets soaked out [27][28].

See also:

Storage

Storing Empty

Burning sulfur sticks/wicks or disks. For the preservation of empty barrels or other wooden vessels, burn 4 g of sulfur per hectoliter of capacity and repeat every 40 - 50 days [29]. To use disks, use a disk holder (e.g. GW Kent sulfur disk holder or create a wire hook to suspend the sulfur disc in the barrel. Light the disc and place into the barrel, inserting a bung to prevent the SO2 gas from escaping. Leave to burn for a few minutes before removing and bunging the barrel for storage.

Note: Do not burn sulfur in used spirit barrels, as there is a risk of explosion. Once a spirit barrel has had a beer aged in it, the ethanol levels within the barrel won't be high enough to cause an explosion. The general rule of thumb is if the spirit can be smelled inside the barrel, don't light a sulfur disc in it.

Ozone [30] [need to expand]

Storing full

A storage solution of 1 g citric acid and 2 g potassium metabisulfite per L (or 1 lb potassium metabisulfite and 0.5 lb citric acid per 225 L barrel[31] (~40 min in)) is often used.

Update: The lined out instructions above have sometimes been advised by wine makers, and presumably taken from their instructions [32]. Jay Goodwin from The Rare Barrel, however, reported sulfur off-flavors in beers from using too much potassium metabisulfite in their barrels. The beers needed extended aging for the sulfur to be volatilized off. Eric Salazar from New Belgium Brewing advised that they cut the potassium metabisulfite powder down to 1 ounce per 59 gallon barrel (~0.017 ounces per gallon/~0.127 grams per liter) [33], and to check the barrel once a month and change the storage solution once a month if needed [34][35]. The amount of citric acid is the same: 0.5 lb per 59 gallon barrel (1 gram per liter/0.13 ounces per gallon) [35]. Before using a barrel holding this sort of storage solution, the barrel should be intensely sprayed and rinsed (not just filled up with hot water and dumped).

Andrew Zinn from Wicked Weed reported that the recommendation above was not enough potassium metabisulfite to prevent microbial growth. They found that 0.3 grams of potassium metabisulfite per liter was the best balance between inhibiting microbial growth while limiting residual sulfur aromas in the barrel. Barrels with this holding solution have been reportedly free of microbial growth for 6+ months. Barrels are only filled with holding solution if they are going to sit for longer than a month; anything earlier than that is sulfured by burning an SO2 tab [36].

Maintenance

(To do) repairing leaks

132 gallon Oloroso Sherry cask with a broken ring. Image provided by Raf Soef.

Misc Info

  • Barrels can be stored upright and used to add fruit to beer. A "punch-down" (punch down) process can be used to gently push the fruit under the surface of the beer to make sure it has contact within the beer, that CO2 is released, and that mold does not form. See "Punch Down Beer", blog article on Funk Factory Guezeria on fruiting in an upright barrel and punching down fruit.
  • Barrels used by some lambic producers (notably 3 Fonteinen and De Cam) were originally 4000 liter barrels used by breweries like Pilsner Urquell. The barrels used for lager brewing are pitched. However, they were rebuilt to hold 1000 liters, and the pitch was removed before being sent to lambic brewers in Pajottenland [37][38].
  • Potassium bitartrate (KHTa) is formed in wine, through the reaction between the bitartrate ion (HTa-), from tartaric acid (H2Ta), and the potassium ion (K+) found in grapes, especially grape skins. It is also known as potassium hydrogen tartrate, and commonly called "Cream of Tartar", "wine crystals", potassium salt of tartaric acid, tartrates, argols, tartres (French), Weinstein (German - "wine stones") [39][40]. KHTa build up appears as crystals in wine barrels. It has no affect on the taste of wine, and is assumed to have no affect on the taste of beer [41][42], however heavy build up of wine crystals can pose a problem [43]. They can be removed from the inside surface of barrels through cleaning with Proxycarb™ or another sodium percarbonate based cleaner such as scent-free Oxyclean™ (see the Barrel Builders Barrel Maintenance Repair Manual).
  • Over sulfuring of sour beer is a somewhat common problem. It often results from using too much sulfur to store in a barrel. Sulfur can also be the result of fermentation. Additional time will eventually allow the sulfur to age out. Other recommendations include running the beer through a food safe copper pipe, purging the beer with CO2, using a wine product called Redules, or even simply transferring the beer from one vessel to another (the small amount of oxygen pick up combined with yeast activity will typically reduce the sulfur) [44].

General Resources and Articles

General Cooperage

Maintenance and Repairs

Racking Canes

Steamers and Cleaners

Pyramid Stacking and Barrel Taps

Bungs

One way ventillation silicone bungs are generally recommended for long aging sour beers in barrels (after primary fermentation) [52].

Manufacturers

Retailers

Waxing Small Barrels

Embrace The Funk Tips

Vinnie Nail

Steps [53]:

  1. When the barrel is full of beer and with a bung in the bunghole to prevent extra spillage, drill a hole using a 7/64 drill bit in the middle of the barrel head. Try not to drill all the way in to avoid mess [54]
  2. Quickly but gently hammer in the 1-1/2" nail the rest of the way. Metric users: substitute nail for a 3mm width by 30mm length nail, and a 3mm drill bit (smaller diameters might not pour well) [55]
  3. Wax around the nail if it keeps weeping.
  4. Choose a tool to remove the nail with. Popular recommendations are: channellock pliers, 9" side cutting pliers, small pry bar, traditional "curved claw" hammer, vice grips [56].
  5. To pull a sample, remove the nail with the chosen tool (remove the bung/airlock as well if there is not enough pressure), take a sample, and then hammer in the nail again. Optional: to avoid messes, remove the nail most of the way with the tool, and then put the tool down and pick up a glass, and remove the mail the rest of the way with your free hand [57].
  6. Keep 2" steel nails handy in case the hole in the barrel head starts to get too big.

Racks

General Barrel Aging Information

Pumps

Milk The Funk Tips and Discussions

Sourcing Barrels - Manufacturers and Suppliers

Pro Sizes

Offers Smaller Sizes

Used Homebrew Sized Used Barrels

Scam Websites

These are sites that have been reported by MTF members as being scam websites pretending to sell oak barrels. We recommend that you do not buy anything from them nor visit their website.

  • OakWoodBarrels.com This website is a scam; do not purchase barrels from them. See this MTF thread.
  • dirtcheapbarrels.com This website is a scam; do not purchase barrels from them. See this MTF thread.

See Also

Additional Articles on MTF Wiki

External Resources

References

  1. ↑ Conversation with Jason Sledd on Milk The Funk. 05/03/2015.
  2. ↑ MTF discussion about bourbon barrels
  3. ↑ 3.0 3.1 Review of quality factors on wine ageing in oak barrels. Garde-Cerdan and Ancin-Azpilicueta (2006)
  4. ↑ Effect of oak barrel type on the volatile composition of wine: Storage time optimization. Garde-Cerdan and Ancin-Azpilicueta (2006)
  5. ↑ Effect of aging in new oak, one-year-used oak, chestnut barrels and bottle on color, phenolics and gustative profile of three monovarietal red wines. Gambuti et al., 2010
  6. ↑ 6.0 6.1 Milk the Funk Facebook Oak discussion
  7. ↑ Milk the Funk Facebook member brew CC
  8. ↑ Milk the Funk Facebook Oak discussion
  9. ↑ 9.0 9.1 Milk the Funk Facebook Oak discussion
  10. ↑ Milk the Funk Facebook Oak discussion
  11. ↑ Basic Brewing Radio barrel progression
  12. ↑ Funk Factory Barrel Waxing
  13. ↑ James Shamas. Milk The Funk Facebook group. 07/13/2017.
  14. ↑ 14.0 14.1 14.2 14.3 Jester King on the Sour Hour part 2
  15. ↑ "5 Tips on Barrel Aging from Avery Brewing Co." Andy Parker on the AHA website. Retrieved 05/10/2016.
  16. ↑ The Sour Hour Episode 16
  17. ↑ Barrel Steam Wand
  18. ↑ Conversation about steaming barrels and bunging on MTF. 05/31/2017.
  19. ↑ Crooked Stave facebook post 2-Nov-2015
  20. ↑ "Chloramine". Wikipedia. Retrieved 09/14/2016.
  21. ↑ "Chlorine". Wikipedia. 09/14/2016.
  22. ↑ "Chlorine Use in the Winery". Christian Butzke. Purdue University. Retrieved 09/14/2016.
  23. ↑ Conversation about steaming barrels and bunging on MTF. 05/31/2017.
  24. ↑ [https://www.researchgate.net/profile/Raffaele_Guzzon/publication/225890726_Survey_of_the_yeast_population_inside_wine_barrels_and_the_effects_of_certain_techniques_in_preventing_microbiological_spoilage/links/5472f6170cf2d67fc035d45f.pdf
  25. ↑ Nate Ferguson of Escarpment Labs. Milk The Funk Facebook thread about using ozone to sanitize barrels. 10/24/2017.
  26. ↑ Wines & Vines website. "Barrel-Washing Protocols". Jan 2013. retrieved 10/24/2017.
  27. ↑ Heat inactivation of wine spoilage yeast Dekkera bruxellensis by hot water treatment. Fabrizio, Vigentini, Parisi,Picozzi, Compagno, Foschino. 2015.
  28. ↑ Brettanomyces bruxellensis yeasts: impact on wine and winemaking. Monica Agnolucci, Antonio Tirelli, Luca Cocolin, Annita Toffanin. 2017.
  29. ↑ 2016. Laffort sulfur disc instruction manual. South Africa
  30. ↑ Ozone sanitation for barrels
  31. ↑ The Sour Hour with Tim Clifford of Sante Adairius
  32. ↑ M&M Wine Grape Co. Citric Acid & Sulfite Barrel Preparation. Retrieved 03/06/2016.
  33. ↑ [https://www.facebook.com/groups/MilkTheFunk/permalink/1648119741882900/?comment_id=1648160011878873&reply_comment_id=1648559265172281&comment_tracking=%7B%22tn%22%3A%22R0%22%7D Mike Makris. Milk The Funk Facebook group. 04/12/2017.]
  34. ↑ The Sour Hour Episode 28 (~49 minutes in). Jay Goodwin from The Rare Barrel. 02/17/2016
  35. ↑ 35.0 35.1 Private correspondence with Mike Makris from The Rare Barrel by Dan Pixley when asked to clarify the amounts that Eric from NBB recommended. 03/06/2016.
  36. ↑ Andrew Zinn. Milk The Funk Facebook group. 05/19/2017.
  37. ↑ Lambicland by Webb, Pollard and McGinn (2010)
  38. ↑ Conversation with Gareth Young and Raf Soef on MTF regarding lambic barrels. 09/22/2015.
  39. ↑ Wikipedia. Potassium bitartrate. Retrieved 09/30/2015.
  40. ↑ Monash Scientific. Potassium bitartrate. Retrieved 09/30/2015.
  41. ↑ Conversation in Milk The Funk about tartrates. 09/30/2015.
  42. ↑ UNDERSTANDING WINE TARTRATES. Jordan Winery. Retrieved 09/30/2015.
  43. ↑ Brandon Jones. Milk The Funk facebook comment on wine crystals. 10/10/2017.
  44. ↑ Conversation on MTF on how to get rid of sulfur in beer. 12/26/2016.
  45. ↑ The Sour Hour Podcast, Episode 39, ~56 minutes in. Jay Goodwin. Retrieved 08/06/2016.
  46. ↑ Brandon Jones. Milk THe Funk Facebook group. 07/11/2017.
  47. ↑ MTF conversation with Brandon Fender regarding cleaning barrels. 08/31/2016.
  48. ↑ Steamer recommendation from Gregory Wilhelm on MTF. 09/06/2016.
  49. ↑ Conversation with Cameron Pryor on steam cleaners on MTF. 11/20/2016.
  50. ↑ Conversation 1 with Cameron Pryor on MTF about a barrel steaming station. 11/20/2016.
  51. ↑ Conversation 2 with Cameron Pryor on MTF about a barrel steaming station. 11/20/2016.
  52. ↑ Question on MTF regarding what type of bung/airlock. 12/24/2016.
  53. ↑ Quoted email from Vinnie Cilurzo on the Burgundian Babble Belt forum. Retrieved 12/1/2016.
  54. ↑ Andrew Zinn on MTF. Drilling a Vinnie Nail. 08/29/2017.
  55. ↑ Mattias Terpstra on MTF. Vinnie Nail diameter for metric. 08/29/2017.
  56. ↑ Various MTF members. Tools for removing a Vinnie Nail. 08/29/2017.
  57. ↑ Sean McVeigh on MTF. Removing a Vinnie Nail without making a mess. 08/29/2017.
  58. ↑ Matt Warren. Milk The Funk Facebook group post. 10/05/2016.
  59. ↑ Private correspondence with The Oak Cooperage by Caleb Buck. 02/13/2017.
  60. ↑ Conversation with Ryan Sealey on MTF regarding Wine Oak Barrels . 01/29/2017.
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