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Master Brewers Association of the Americas > BREWING RESOURCES > Ask the Brewmaster
July 15
DMDC anti-microbial additive

Q: Awhile back I noticed the TTB approval of Dimethyl Dicarbonate (DMDC) as a processing aid in beer production, but I haven't seen anything more written about it. Can you tell me a little about this option? The TTB release describes it as a "microbial load reducer" and I can find a number of resources that cite its use in winemaking. They seem to use it to reduce wild yeasts. Does DMDC have any effect on beer-spoiling bacteria? Is this a product we'll see beer suppliers carrying in the near future? An overview of processing instructions or help identifying further resources might be useful as well.

A: The commercial name is Velcorin and it has been used in soft drinks and wines (usually low alcohol sweet wines with some residual sugars) for some time, mostly in South America and South Africa.  It has recently been approved for use in both wine and beer in the US and at least one large US winery is studying its use in sweet, low alcohol wines.  Velcorin is effective against yeast, bacteria and molds.  It penetrates the cell membrane and targets certain enzymes which results in the cells lysing (opening up) and re-fermentation is almost impossible. You can find out more at www.velcorin.com.


July 08
Recapturing rinser water

​Q: You had mentioned that you had some experience with reclaiming bottle rinse water and sending it through the filler vacuum pump and possibly into a pasteurizer. Do you recall if there was any filtration of the water? Was there some sort of a storage tank for the water? We really see this as a great opportunity with 3 bottling lines and 2 can lines and any insight would be GREATLY appreciated.

A: The rinse water recovery is low hanging fruit but will need a receiver tank, float control for fresh water refill and a pump.  We let the water from the rinser fall by gravity into a receiver tank and then pumped that water through the vacuum pump to cool the seal.  If the water level got low (rinser had shut off) then the float would open a fresh water valve and keep the tank full so the seal would not run dry and overheat.  We then would collect the water out of the vacuum pump and into another receiver and pump that water (now slightly warm) to shower off bottles coming off the crowner.  The shower water would go to drain.  This way we used the water 3 times and saved an appreciable amount off the water and sewer bills.  You could use the water out of the vacuum pump in a pasteurizer as well.

June 16
Installing brewery flooring

​Q: I just read your article on building a brewery floor.  My Husband is a brewer, looking for a commercial spot to set up shop.  However, all the warehouses we have looked at do not have a floor drain.  I know we will have to install a pad and somehow create a slope going in to a drain.  Do you know of any other type of set up (other than breaking the concrete) and/or material to create the pad? Many property owners do not like the idea of concrete and would rather we bring in a different (hopefully portable) material.

A: To make beer you will need some kind of floor drain system.  Some people use berms and then wet the floor down to see its natural low spot and that is where the drain goes.  However this cheap and cheerful method results in the same concrete cutting to install the drain and piping as a proper system and requires a squeegee and lots of effort to actually use.  Not recommended!  The options for you to install a properly drainable floor, ie one that works, are the following:

• Take out the floor and pour new slab with proper re-bar reinforcement after installing trench drains and drain piping.  Slope at ¼-5/16” per foot to the drains then seal with epoxy type mortar
• Pour a topping slab over the existing concrete floor (if it can take the weight load of your equipment), with same slope and sealing as above suggestion
• Use a grout system and hardened tiles to the trench drains using the same kind of slope

Sorry but unfortunately there no portable/temporary systems out there (yet).

June 16
Yeasty flavors in bottle conditioned beers

​Q: What flavor does dead yeast leave in bottle conditioned beer?

A: bottle conditioned beers can have 0.5 million cells per ml or more to complete the bottle fermentation and carbonate the beer.  If the beers after bottling are subjected to higher temperatures in storage then they can develop meaty-brothy flavors.

April 22
Passivation of stainless steel vessels

​Q: We are having some debate as to passivisation techniques, so I was hoping you could shed some light on what is best practise. In particular, could you clarify the different methods of passivisation in terms of chemicals used (and at what concentrations), time, temperature, and whether or not rinsing is desirable?

A:  There is no definitive answer to this question but the main objective to passivation of stainless steel tanks and vessels is to eliminate tramp iron deposits and establish a layer of protective chromium oxide to resist corrosion.  I have asked two experts with a lot of experience in this area, Joe Dirkson of EcoLab and Ashton Lewis of the Paul Mueller Company to comment.

Joe's response is based on the traditional method of passivation involving a strong oxidizing Nitric acid solution:

Stainless steel derives its corrosion resistance from a very thin layer of chromium oxide that forms at the metal surface when exposed to oxygen in the air. The chromium oxide film can form in air if the stainless steel is clean and dry. So the passivation process is really about making sure that all contaminants are removed from the surface, then allowing the surface  to dry, so that the passive layer can form.

New vessels and piping may have a variety of soils, including polishing oil, EP (extreme pressure) additive oils, adhesive film and tramp iron (polishing dust).  All of these soils must be completely removed.

The following steps are recommended for effective passivation. High chemical concentrations are required  - consult the Safety Data Sheet prior to chemical use.  Be sure to wear appropriate PPE. 
1. Inspect the metal surfaces for any soil, film, deposits or extraneous material.  Use a flashlight.  A digital camera is helpful to document the surface appearance.
2. Check with the equipment supplier to determine if the manufacturer/supplier has any special restrictions or cautions about passivation – want to be sure to not invalidate the equipment manufacturer’s warranty.
3. Assuming a CIP system is available, rinse the tank with water.  Note, avoid water that has a high (greater than about 50-75 ppm) chloride ion content.  High chloride content can lead to pitting corrosion.
4. Wash the tank with a strong caustic solution.  Some caustic products are specially formulated for washing new tanks – check with your chemical supplier about specific products.  Circulate for one hour at 140-150F.
5. Rinse the tank with water until neutral. Observe sheeting action during the rinse.  If the tank is satisfactorily clean, the rinse water should sheet over the surface.  Any streaking or spots indicates incomplete cleaning. Burst rinsing is recommended.
6. Repeat the caustic clean as necessary.
7. Wipe the surface with a soft white cloth.  Inspect for any particles or brown film.  Brown film can be either tramp iron dust (polishing dust) or oil.  Polishing dust can be confirmed by holding a lab magnet onto the dry cloth – iron particles will adhere to the magnet. .
8. To remove tramp iron dust, first the surface should be washed with a cationic detergent to minimize static charge.   Apply a cationic detergent by foam or CIP.  Brush wash if necessary.  Rinse.
9. Circulate a strong nitric acid solution for one hour at 140-150F.   A concentration of 10-20% active nitric acid by weight is recommended to dissolve all tramp iron.  Note, nitric acid is significantly more effective than citric acid in terms of dissolving tramp iron. Excercise extreme caution with this strong acid solution!
10. Rinse.  Repeat the white cloth test to validate that all tramp iron has been removed.  Repeat the acid wash as necessary.
11. Allow the surface to dry completely.  Dry time can vary depending on temperature, and air exposure.  For pipes and surfaces that are not readily exposed to air, 72-hour dry time is recommended.
12. Prior to equipment startup, run a normal CIP cycle and sanitize.
Ashton's response is based on a less aggressive solution of Citric acid incorporated with EDTA:

The old stand by method is to use hot, highly concentrated nitric acid.  Nitric is a strong oxidizing acid capable of dissolving iron from the surface of stainless steel alloys.  Since it is a strong oxidizer it also actively forms a very thin layer of chromium oxide; this is the "passive" layer that protects stainless steel alloys from corrosion.
The problems with this method are numerous: this can be dangerous to personnel, it can damage elastomers and it is problematic for disposal to municipal wastewater systems.  I was on a start-up of a pasteurizer at a large rum producer's facility and an outside chemical contractor came in to passivate the equipment we installed.  They insisted on using 50% nitric acid heated to 160F for the operation.  I was extremely nervous for the entire operation.  This person then insisted on dumping the solution after each use and this turned out to cause some problems with the plant's effluent treatment system.  We have pharmaceutical customers who use this method and they change out ALL of the elastomers in their system after passivation.  In a large process module this is an expensive and time-consuming endeavor.
An alternate method is to use a citric acid solution that has been pH adjusted and enriched with EDTA.  Citric acid forms a complex with free iron and is an effective and safe method to perform the first step of passivation.  At Mueller, we use the citric acid method because the nitric acid method is simply too dangerous.  Years ago I was discussing this topic with someone at a major global brewer and learned that they also have an approved citric acid method.  Talk to your chemical supplier about options using a citric acid/EDTA solution.
With any new cleaning/passivation method it is very important to test the methodology on a small sample of equipment to verify that the procedure does not damage equipment.  I do not mean to suggest that 50% hot nitric used on Type 304 stainless needs to be tested before use, but if a solution with some unknown additives is applied to "stainless steel" with unknown alloy composition the user should really do some testing before exposing a whole new tank to the method.  I have heard some unpleasant stories about foreign steel with unknown composition being damaged during cleaning.


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Have you ever had a brewing, brewery, or technical question but didn't know who to ask?
Send your questions or comments or recipes to the MBAA Technical Director Karl Ockert.
Karl will post questions and answers as frequently as possible in a blog format as a benefit to all MBAA members.


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