In the production of beer, a warm water extract of barley malt, with or without other unmalted grains such as rice or corn, is boiled with hops, cooled, and then subjected to the fermentative action of yeast. The warm water used to extract the malt allows the action of several enzymes in the malt to hydrolyze the starch in the barley (and in the corn or rice) to fermentable sugar.

As a result of material contained in the ingredients, or the mashing process, or the fermentation process, or a combination of two or more of the above, malt beverages are subject to an oxidative change in flavor. The resulting flavor is variously described as papery, cardboard-like, stale, or just plain"oxidized". This flavor change typically takes place within 2-3 months of room temperature storage, and is gradual and continuing. Most American manufacturers of beer recall beer from the market if it is more than about 4 months from the packaging date. Although the oxygen in a bottle or can of beer is typically consumed by the beer within less than 24 hours after packaging, the noticeable presence of oxidized flavor generally does not appear until many weeks later.

The flavor of oxidized malt beverages generally is attributed to unsaturated aldehydes notably trans-2-nonenal, and related compounds.

These compounds are thought to be derived from unsaturated fatty acids, which split and then lose two hydrogen atoms. This loss of hydrogen is a form of oxidation.

The present practice of delaying the staling of beer is to maintain a low level of air (or oxygen) in the packaged beer, storing the beer at cold temperatures, and/or by the addition of sulfites, within legal limits, prior to packaging.

Modern beer-filling machines are designed to achieve very low air levels in the packaged product. Typically, the present practice is to evacuate the bottle before it is filled with beer, or to replace the air in the evacuated bottle with carbon dioxide before filling, and to cause overfoaming in the bottle to displace the head space gases with beer foam. All of these practices can produce air levels of less than 0.5 ml. per 12 oz. bottle. But even these low levels of air still allow beer to oxidize in 2-3 months.

Another technique for stabilizing beer against oxidation is to add sulfur dioxide, in the form of bisulfite, to the beer. However, in the United States, addition of sulfur dioxide is limited by law to less than 10 ppm, and even those low levels produce undesirable and sulfury aromas in some beers.

Also the bisulfite, which works by binding to aldehydes, has many other aldehydes in beer to bind to (notably acetaldehyde, a normal by-product of fermentation), and so its action is often muted. Other countries such as Germany prohibit any addition of sulfur dioxide.

In my prior U. S. Patent No. 5,455,052,1 describe a method of improving the stability of a malt beverage to oxidation, which comprises adding to the malt beverage about 0.01 to about 50 parts per million, by weight, of a lactone selected from the group consisting of gamma-nonalactone-gamma- undeclatone, and mixtures thereof. While the addition of a lactone to a beer as above-described advantageously has been found to stabilize beer against oxidation, the addition of a lactone (or other ingredients) is frowned upon by beer purists, and is prohibited under the brewing purity laws in countries such as Germany.

It is thus a primary object of the present invention to provide a process for enhancing the flavor stability of a malt beverage. A more specific object of the present invention is to provide a malt beverage in which oxidative flavor does not begin to appear for many months of storage.

I have found that the exposure of malt beverages to dried, toasted oak wood (Quercus alba and/or Quercus robus), in particulate form, i. e. shavings, chips, powder or other small entities, for a period of from one day to several weeks, provides flavor stability to the malt beverage for periods up to one year or longer.

Further objects and advantages of the invention shall be apparent from the following detailed description, taken in connection with the accompanying drawing, Fig. 1, which illustrates a preferred embodiment of the present invention, in partial cross-section.

The exposure to the oak wood particles is done after the main fermentation, during the aging process, but also may be done before or after the standard aging stage. The aging process may be conducted in any of the three standard aging methods-simple lagering (allowing fermented beer to be stored for several days or weeks in a tank); second fermentation (removing the settled yeast from a fermenting tank before the fermentation has been completed and allowing fermentation to slowly proceed to or near the limit of fermentation); or krauesening (treating of freshly fermented beer with a small portion, about 15% by volume, of beer that just started fermenting a day before). The addition of the oak wood particles preferably is done at the inception of the aging process.

When using oak wood particles in accordance with the present invention, the wood particles should be wood, as it comes form a tree i. e. the oak wood particles should not be washed with detergent or other alkaline solution, nor steamed, and the oak wood particles should not be coated, e. g. with wax or pitch. Moreover, the oak wood particles should be used for a

single batch, and discarded. On the other hand, the oak wood particles must be dried and toasted in air, under controlled conditions, i. e. at a temperature between about 300°F and about 500°F, to a moisture content of about 0.5% to 1% by weight, preferably about 1% by weight, prior to use. In order to ensure low moisture content prior to use, the oak wood particles preferably are stored in an airtight container after toasting. Also, the dried oak wood particles, which have low density and poor wetting characteristics, tend to float on the foam on top of the beverage as the tank is being filled. In order to ensure intimate and lasting contact between the oak wood particles and the beverage, the oak wood particles preferably are loosely packaged in a porous or permeable fabric bag or container which is weighed down with a dense material such as glass, stainless steel or other dense material which is inert to the beverage, such that the wood-particle containing bag or container sinks in the tank or remains suspended in the beverage, but does not float to the top.

Alternatively, the wood particle-containing bag or container may be tied to a cleat on the side or bottom of the tank, or to a cooling coil or the like in the tank, or the container may be tied to an anchor.

The flavor stabilizing improvement appears to be dependent upon the quantity of oak wood particles added. Thus, the oak wood particles should be added in an amount of about 0.05 lbs. per 100 lbs. of malt beverage (or 0.13 lbs. per bbl. of malt beverage). Addition of less than about 0.01 lbs. per 100 lbs. of malt beverage (or 0.03 lbs. per bbl. of malt beverage) appears to result in little improvement in flavor stability. On the other hand, addition of more than about 0.8 lbs. per 100 lbs. of malt beverage (or 2.0 lbs. per bbl. of malt beverage) appears to result in little additional improvement in flavor stability.

The reason why the addition of oak wood particles to a malt beverage improves flavor stability is not known. However, while not wishing to be bound by theory, it is known that oak contains various organic acids,

aldehydes and phenols and tannins, one or more of which may impart the oxidation--stabilizing effect in beer.

Historically, and to a lesser extent today, beer was/is stored in wooden tanks of cypress, chestnut or oak. However, direct contact of the beer with the wood was/is scrupulously avoided by coating the wood, for example, with a paraffin-type wax or pitch. This is because the contact of wood with beer has been found to cause microbiological problems and musty flavors in the beer if the wood is not coated and re-coated as time goes on. Thus, it was/is common for wooden tanks used in breweries to be re-coated annually or bi- annually to prevent such contact and ensuing microbiological problems in flavors. In the United States and most other countries, stainless steel largely has replaced wood for beer containers today. Wooden barrels also once were used to deliver beers to bars. However, such wooden barrels typically were re-coated every time they were returned to the brewery. Today, wooden barrels have essentially been completely replaced by stainless steel barrels.

Moreover, aging or storing the beer in wooden tanks or casks does not provide the desired and unexpected stabilizing result in any event.

A major U. S. brewery claims to use beech wood chips in its aging process. However, such chips are used only after they have been washed with caustic solutions to remove any soluble material from the wood. And, these chips, which are used many times and washed after every use, are used merely to serve as mechanical supports, i. e. provide more surface area, for action of the yeast which settles on the chips.

Toasted, dried oak wood (Quercus alba and/or Quercus robus) appears to be unique in stabilizing beer against oxidation. Other wood particles have been tested and are found not to provide a similar effect.

The flavor stabilizing improvement appears to be independent of the size and form of the oak wood particles; however, for a given weight, smaller particles appear to require a shorter residence time to achieve the desired

result. It is believed that this is because the smaller particles have a relatively larger surface area which facilitates extraction of the materials which impart the oxidation stabilizing effect in accordance with the present invention. The toasted oak wood particles should be used to process a single batch, and removed, and discarded.

The resulting malt beverage has superior flavor stability over similar malt beverages made without the addition of toasted oak wood particles, and none of the disadvantages of undesirable and sulfury aromas common to prior art techniques for stabilizing beer against oxidation by the addition of a bisulfite.

The present invention will be further described in the following working examples.

White oak wood chips (Quercus alba) were prepared by planing white oak stock. The chips were placed in an oven and heated to 300-500ouf for about 30-90 minutes, until they were browned slightly, and the moisture content measured about 1 % by weight. The toasted chips 10 were allowed to cool, packaged in a porous cotton bag 12 to which was added sufficient stainless steel shot 14 as ballast to overcome any buoyancy of the wood chips.

The cotton bag was then tied closed at 16, and the bag placed in a plastic storage bag 18 pending use as described below in the following working examples.

Preparation A was repeated, however employing red oak particles (Quercus robus) and glass beads as ballast.

EXAMPLE I Twenty-five thousand lbs. of barley malt were ground and added to 200 bbls. of water at 122°F in a mash tub. After resting for 20 minutes, the temperature was raised to 165°F and held for 40 minutes. It was then brought to 175°F and the mash transferred to a lauter tub and filtered.

The filtered wort, about 520 bbls., was boiled with 200 lbs. of hops for one hour.

The wort was cooled, aerated, and pitched with yeast, in a fermenting tank, where it remained for 7 days.

It was then transferred to an aging tank, in which had been placed 4 cotton mesh bags, each filled with 30 lbs. of toasted white oak particles and 1 1/4 lbs. of stainless steel saddles, and tied closed. Then 500 bbls. of beer was pumped into the tank and the tank closed. It was allowed to remain for two weeks.

The tank was emptied, the beer filtered and finished. The bags of oak were removed, and the stainless steel saddles removed and the oak discarded.

The beer was packaged and subjected to accelerated aging at 100°F for 45 days. The beer was tasted by a panel trained to detect and rate oxidation in beer. On a scale of 0 to 5, with 5 being thoroughly oxidized, the control beer was rated 5 and the oak-treated beer was rated 1.

EXAMPLE II Twelve thousand lbs. of corn grits and 1,000 lbs. of malt were added to 150 bbls. of water at 120°F, allowed to remain there for 10 minutes and then heated to boiling and boiled for 30 minutes.

In another vessel, 15,000 lbs. of barley malt were added to 200 bbls. of water at 120°F, allowed to rest for 20 minutes, and then the boiling corn mash was added to it. The temperature was kept at 160°F for 35 minutes and then raised to 170 °F and transferred to a lauter tub and filtered.

The wort was cooled, aerated, pitched with yeast and allowed to ferment.

At the end of fermentation, the beer 500 bbls., was transferred to an aging tank to which had been added 150 lbs. of toasted red oak chips (1 % moisture) and 50 lbs. of glass beads, separated into three porous woven nylon bags, and tied closed.

After 18 days, the beer was moved to another tank and filtered. The three bags and oak chips were discarded, after the glass beads were recovered and washed.

The filtered beer was packaged in 12 oz. Bottles and subjected to the same accelerated aging as in Example I.

The results of tasting with the same trained taste panel were the same.

Certain changes may be made without departing from the scope of the invention herein involved. For example the porous container could comprise a perforated stainless steel container, in which case ballast may not be required. Also, the container may include one or more ties or eyelets shown in phantom at 18 and 20, respectively, for tying the container down to the tank, and/or to an anchor (not shown). It is therefore intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.